The Dry April That Wasn’t

April ended colder and wetter than average across the state. The preliminary statewide average April temperature was 49.2 degrees, 3.4 degrees below the 30-year normal and tied for the 27th coldest on record going back to 1895. The preliminary statewide average total April precipitation was 4.36 inches, 0.58 inches above than the 30-year normal and the 43rd wettest on record.

Data are provisional and may change slightly over time

April Temperature Rollercoaster

Warm weather spilled over from March into the beginning of April. Average temperatures between April 1 and April 10 ranged from 1 to 6 degrees above the 30-year normal across the state. A strong cold front moved through the region between April 9 and 11, with following unseasonably cold air that quickly decreased temperatures. Average temperatures between April 11 and 20 ranged from 5 to 15 degrees below normal (see maps below).

Many stations across the state recorded daily maximum temperatures in the mid- to high 80s during the first 10 days of April, only to record daily minimum temperatures in the mid- to low 20s in the second 10 days. For example, stations in McHenry and Woodford Counties recorded high temperatures of 82 degrees on April 9 and one week later recorded low temperatures of 20 degrees on April 16. Fourteen stations around the state broke daily April high maximum temperature records and three stations broke daily April high minimum temperature records between April 7 and 12. Subsequently, 20 stations broke the daily April low maximum temperature records and 30 stations broke the April low minimum temperature records between April 13 and 20.

The plots below show daily maximum and minimum temperatures, as well as daily average temperature departures from normal, for April in Jacksonville. The average temperature in Jacksonville on April 8 was nearly 20 degrees above the long-term average, and the average temperature 10 days later on April 18 was nearly 20 degrees below the long-term average.

Overall, April average temperatures ranged from the low 30s in northern Illinois to the mid-50s in southern Illinois. April was cooler than normal across the state. The preliminary statewide average April temperature was 49.2 degrees, 3.4 degrees cooler than normal and the 27th coldest on record back to 1895. April ended the consecutive four-month streak of warmer than normal months going back to December 2019.

Spring Freeze

As a result of the strong cold front that moved through the region in mid-April, minimum temperatures dipped below freezing as far south as Pope County. Stations in northwest Illinois recorded minimum temperatures in the teens on April 8. Late-season freeze events in early to mid-April are not uncommon; however, last month’s event followed a prolonged period of well above average temperatures. The plot below shows daily average temperature departures from the 30-year normal from March and April in Carbondale. Between March 1 and April 12, Carbondale experienced twice as many warmer than normal days than cooler than normal days. Furthermore, the minimum temperature in Carbondale last dipped below freezing on March 7 before reaching 30 degrees on April 14.

Flowering trees, shrubs, and tender perennials broke dormancy and began to green in response to prolonged warm conditions throughout March and early April. This increased the vulnerability of Illinois specialty crops such as peaches, strawberries, and asparagus to the late-season freeze. University of Illinois Extension reported some damage to specialty crops in most regions of the state as a result of the freeze event in mid-April. The extent of damage was likely curtailed by successful warming of the sub-freezing temperatures five to seven days prior to the event.

Heavy Late-April Rain

The first two-thirds of last month was somewhat to very dry across the state, with most areas experiencing less than 50 percent of normal precipitation by April 20 (see maps below). The station in Rosiclaire in Hardin County recorded less than one-half an inch of rainfall in the first 22 days in April, putting last month on track for one of the driest Aprils on record. Likewise, areas of east-central Illinois were experiencing a 2-inch precipitation deficit by April 22. The prolonged dry conditions caused soils to dry considerably. Both 4-inch and 8-inch soils at the Illinois Climate Network station in Bondville in Champaign County were at their driest April levels since 2012. The dryness was quite a contrast to April 2019 and was beneficial for farmers to make planting progress.

The dry weather was brought to an abrupt end by a series of storms that tracked across Illinois over the last week in April, generating very heavy rainfall and widespread 2- to 4-inch accumulations along the Interstate 55 corridor between the St. Louis Metro East and Chicagoland (see map below). The heaviest rainfall was in central Illinois between Mason and McLean Counties.

The Bloomington Waterworks station recorded 4.99 inches on April 26, which was the largest single-day April precipitation event on record at that station going back to 1949. The wettest point in the state last month was Havana in Mason County. The Havana station recorded just over 2 inches of precipitation in the first 22 days of April and was experiencing nearly a three-quarter-inch precipitation deficit at that time. Havana received nearly 6 inches of precipitation in the following seven days and ended the month with an all-time April record-breaking precipitation total of 7.8 inches (see plot below).

Heavy precipitation in late April caused flash flooding across central and northeastern Illinois as well as inundated fields and resultant planting delays. Additionally, many gauges along the Illinois River, Des Plaines River, and Mississippi River south of Hardin were pushed into the flood stage.

Total March precipitation ranged from just under 8 inches in central Illinois to less than 2 inches in southeastern and northwestern Illinois. These totals ranged from over 175 percent of average April precipitation in central to less than 50 percent of average April precipitation in southern Illinois.

Overall, the preliminary statewide average April precipitation was 4.36 inches, 0.58 inches above than the 30-year normal and the 43rd wettest on record. The April average does not reflect the 5- to 6-inch differences in precipitation between central and northern/southern Illinois.

Most of the northern half of the state experienced measurable snowfall last month. April totals ranged from over 8 inches in north central Illinois to just over one-tenth of an inch along Interstate 72. A single storm in mid-April produced widespread 24-hour snowfall totals between 1 and 3 inches in central and northern Illinois, with a few much larger isolated totals. Areas of Warren, Henry, Knox, and Mercer Counties received more than 6 inches of snowfall in a single day, including the third and fifth highest single day April snowfall totals in Kewanee and Galesburg, respectively. This event was also the latest 5-inch or larger snowfall event on record at nearly a dozen stations around the state.

With April on the books, the total 2019–2020 season snowfall ranged from over 50 inches in far northern Illinois to less than 1 inch in southeastern Illinois. Most areas of the state north of Interstate 70 experienced a snowier than average season (see maps below).

Outlooks

Short-term 8–14-day outlooks from the NOAA Climate Prediction Center show strongly elevated odds of below normal temperatures and slightly elevated odds of above normal precipitation across the state.

Longer-term 30-day outlooks are similar to the 8–14-day outlooks, with continued, albeit weaker, chances of cooler and drier conditions, especially for the northeastern half of the state for May. 

 

Warm, Wet, and Active Spring

March was warmer and wetter than average across the state, continuing the pattern from winter. The preliminary statewide average March temperature was 43.5 degrees, 2.20 degrees above the 30-year normal and the 28th warmest on record going back to 1895. Preliminary statewide average total March precipitation was 3.96 inches, 1 inch wetter than the 30-year normal and tied for the 34th wettest on record.

Data are provisional and may change slightly over time

Persistent Warmth in March

Much like the first two months of 2020, March temperatures were consistently above the long-term average.

The first two months of the climatological winter season were much warmer than average, with very few cold air incursions. The plot below shows the March daily average temperature as a departure from average in Rockford. Since the start of 2020, over 70 percent of days in Rockford have been warmer than the long-term average. This has caused 2-inch and 4-inch soil temperatures to generally remain above freezing over this time, according to observations from the Illinois Climate Network (https://www.isws.illinois.edu/warm/soil/).

Average temperatures in March ranged from the high 30s in northern Illinois to the low 50s in southern Illinois. Temperatures ranged between 1 and 5 degrees above the long-term average. The statewide average March temperature was 43.5 degrees, which is 2.20 degrees above the 30-year normal and tied for the 28th warmest on record. March marked the fourth consecutive month with statewide average temperatures above the 30-year normal. By comparison, the first three months of 2019 were all 1 to 3 degrees below the 30-year normal, considerably cooler than 2020 so far.

The warm weather in March resulted in three daily high maximum temperature records and seven daily high minimum temperature records being broken across the state. The few cold, cloudy days we had in March also resulted in six daily low maximum temperature records and one daily low minimum temperature record being broken across the state. The long-running station in Carbondale was only 1 degree away from its all-time March high minimum temperature record on March 28, thanks to a strong mid-latitude warm sector bringing warm air from the south. Multiple stations in southern Illinois recorded daily maximum temperatures at or over 80 degrees during the last week in March. At one of these stations, Fairfield in Wayne County, this was two weeks before the average first 80-degree day based on the long-term record.

The highest temperature recorded in the state in March was 81 degrees in Alexander, Pope, and Hardin Counties, while the lowest temperature was 8 degrees in Jo Daviess, Knox, and Whiteside Counties.

Storms Bring Heavy Rain to Northern and Southern Illinois

Frequent precipitation persisted from February into March for the southern part of the state. Most areas south of Interstate 64 received over 6 inches of total precipitation in March, and some areas received over 8 inches. This represents between 150 percent and 200 percent of normal March precipitation in southern Illinois (see map below). Most stations in southern Illinois received 50 percent or more of their total March precipitation in one 24-hour period between March 20 and 21, thanks to a series of storms that tracked across the region.

One-day precipitation totals reached 4.50 inches in Clay County, which set the all-time March one-day precipitation record at the station in Clay City and broke the previous record by over three-quarters of an inch. Other large one-day totals from the March 20 storms included 3.85 inches in Mt. Vernon in Jefferson County and 3.55 inches in Olney in Richland County. With these one-day totals subtracted, March 2020 was very close to March 2019 total precipitation in southern Illinois; however, because of this event, most areas in southeast Illinois received between 1.5 and 2.5 times the amount of March 2019 precipitation this month.

Although March precipitation totals in northern Illinois were not as generous as those in the south, northern Illinois was not averse to very large one-day precipitation totals. A series of storms that moved through on March 28 generated between 3 and 4 inches of precipitation in a less than 24-hour period for a stretch of Illinois between the Quad Cities and the western suburbs. One CoCoRaHS observer in Prophetstown in Whiteside County recorded 5.34 inches on this day. Unfortunately, the heaviest precipitation missed the longer-term COOP stations in the region, but the storm did manage to break the all-time March one-day precipitation total in DeKalb.

Total March precipitation ranged from over 8 inches in far southern and southeast Illinois to just over 2 inches in central Illinois. These totals ranged from over 200 percent of average March precipitation in southeastern and northern Illinois to just over 75 percent of average March precipitation in western Illinois. Most of central Illinois received between 75 percent and 125 percent of average March precipitation. This combined with above average temperatures allowed soils to dry a bit across central and western Illinois.

Last month was the wettest March on record at Rock Island Lock & Dam 15, with 6.17 inches recorded. The wettest place in the state last month was Clay City with 8.31 inches.

Overall, the preliminary statewide average total March precipitation was 3.96 inches, exactly 1 inch more than the 30-year normal and the 34th wettest on record. Although the March average does not reflect the 5- to 6-inch differences in precipitation between central and northern/southern Illinois.

Most of the northern half of the state experienced measurable snowfall last month. March totals ranged from around 6 inches in northeast Illinois to just over one-tenth of an inch along the Interstate 70 corridor. A winter storm on March 22 and 23 accounted for the vast majority of snowfall in the northern part of the state, with one-day totals exceeding 6 inches in Grundy County. Morris in Grundy County was the snowiest point in the state in March, with just over 7 inches of total snowfall.

March total snowfall departures mimic the spatial patterns for the entire winter season. Most areas of western, northwest, and west-central Illinois had totals within 5 inches of the long-term average, whereas most counties south of Interstate 70 as well as counties in the Chicagoland metro area have experienced 5 to 10 inches below average snowfall since the first snow of the season.

Severe Weather

Illinois experiences severe weather and storms in all calendar months, but March often begins the unofficial severe weather season. This last month we had numerous severe weather and storm reports, ranging from snowstorms to large hail and a few tornadoes. Trained spotters reported 2-inch hail in both Williamson and Vermilion Counties last month, with many more reports of 1.5- to 1.75-inch hail across southern and central Illinois. The AWOS station in Hyde Park in Cook County recorded a 61 mph non-thunderstorm wind gust on March 29. Finally, multiple tornadoes were reported in Illinois last month in southern and west-central Illinois, including three tornadoes between Peoria and the Quad Cities on March 28. One of these, an EF-1 tornado, developed just a quarter mile east of the Peoria International Airport, according to the Lincoln National Weather Service https://www.weather.gov/ilx/032820Tornadoes).

 Outlooks

Short-term 8-14-day outlooks from the NOAA Climate Prediction Center show strongly elevated odds of both above normal precipitation and above normal temperatures across the state.

Longer-term 30-day outlooks are similar to the 8-14 day outlooks, with continued elevated chances of warmer and wetter conditions across the state for April.

Heavy precipitation in northwest and southern Illinois, combined with continual snowmelt in the Upper Midwest has continued the threat of flooding along most major rivers in Illinois. Currently, gauges along the Mississippi, Ohio, Illinois, and Wabash Rivers are at or above minor flood stage, with nine gauges in moderate flooding, according to the National Weather Service River Forecast Center.

A typical February ends an otherwise atypical winter

February was slightly warmer and wetter than average across Illinois, bringing an end to a very warm climatological winter season. The preliminary statewide average February temperature was 31.2 degrees, 0.30 degrees above the 30-year normal and tied for 42nd warmest on record. Preliminary statewide average total precipitation for February was 2.13 inches, 0.07 inches wetter than the 30-year normal and tied for 46th wettest on record.

Data are provisional and may change slightly over time

Mostly Warm, Briefly Cold in February

The first two months of the climatological winter season were much warmer than average, with very few cold air incursions. As the temperature plot from Bloomington shows (below), February started consistently warmer than average, but multiple cold air incursions in the latter half of the month led to an overall near-normal temperature month.

Average temperatures in February ranged from the high teens in northwestern Illinois to the high 30s in southern Illinois. Average temperatures ranged within a degree of the long-term average for all but a southeast sliver of the state. The statewide average February temperature was 31.2 degrees, which is 0.30 degrees above the 30-year normal and tied for 42nd warmest on record.

The warm weather that started the month resulted in 115 daily high maximum temperature records and 12 daily high minimum records being broken across the state. One truly incredible departure was a 70 degree high temperature in Charleston in Coles County on Feb. 3. This was nearly twice the long-term average daily high temperature of 38 degrees for that calendar day in Charleston and 5 degrees above the previous record. Eleven days later the Charleston station broke its daily low maximum temperature, reaching only 15 degrees on Valentine’s Day. In total, cold air incursions in February resulted in 23 daily low maximum temperature records and 34 daily low minimum temperature records being broken, most of which were recorded on Valentine’s Day.

The highest temperature recorded in the state in February was 72 degrees in Effingham County, while the lowest temperature was -18 degrees in Jo Daviess County.

An End to a Very Warm Winter Season

February brought an end to climatological winter, which will be best known for persistently warmer than average weather. The preliminary December to February statewide average temperature was 32.6 degrees, which would result in this being the 12th warmest climatological winter season on record in Illinois.

This winter season’s mildness is characterized well by the Accumulated Winter Season Severity Index (AWSSI), which uses daily accumulation of points, based largely on temperature, to characterize winter season severity. The map below shows accumulated winter season severity as of March 3 for individual stations across the U.S. All stations in Illinois have so far exhibited a mild or moderate winter season (i.e., below average severity). AWSSI data and maps are created by the Midwestern Regional Climate Center (https://mrcc.illinois.edu/research/awssi/indexAwssi.jsp).

Wet South, Dry North

Winter precipitation depends strongly on the location of the subpolar jet stream, which often characterizes the track for winter storms. Last month storms tended to track south of the state, bringing the most rain to southern and south-central portions of Illinois. Total February precipitation ranged from over 10 inches in far southern Illinois to just over a tenth of an inch in northwestern Illinois. These totals range from over 150 percent of average February precipitation in southern Illinois to less than 25 percent of average in northern Illinois.

This was the driest February on record at Gladstone Dam in Henderson County, with only 0.04 inches of precipitation recorded, despite the extra February day this leap year. The wettest place in the state last month was Cairo in Alexander County, with 7.34 inches total precipitation.

Overall the preliminary statewide average total February precipitation was 2.13 inches, 0.07 inches wetter than the 30-year normal and tied for 46th wettest on record. As a point of reference, the statewide total precipitation for February 2019 was 3.21 inches and for February 2018 it was 4.88 inches.

While southern Illinois was experiencing persistent rain, most of northern Illinois was treated to abundant snowfall in February. Snowfall totals from last month ranged from just over 15 inches in Kane County to less than an inch along Interstate 70. Thanks to a mid-month storm, a small area of Mason, Cass, and Menard counties received 6 to 8 inches more than average snowfall in February, whereas most of the rest of the state north of Interstate 70 received near average to just a couple of inches above average snowfall last month.

Snowfall totals over the climatological winter season (December–February) are within 5 inches of the long-term average for most of the central and western portions of the state, while a snowfall deficit exists along the Indiana border and for most of southern Illinois. The largest departures from average are in the Chicagoland area, where winter season snowfall has been 15 to 20 inches less than average.

Outlooks

Short-term 8- to 14-day outlooks from the NOAA Climate Prediction Center show strongly elevated odds of both above normal precipitation and above normal temperatures across the state.

Longer-term 30-day outlooks show probabilities remain elevated for warmer than normal conditions across the state for the remainder of March, while elevated probabilities of wetter a wetter than normal March persist in the southern half of the state.

Spring flooding outlooks from the National Weather Service continue to show above normal to much above normal risks of flooding in the Mississippi River Basin, including 473 gauges with a 50 percent or greater chance of flooding between March and May (see below). Most gauges along the Mississippi River in Illinois have a 50 percent or greater chance of major flooding this spring, with gauges along the Illinois, Kaskaskia, Wabash, and lower Ohio rivers having a similar chance of minor to moderate flooding before May.

The elevated flood risk is due to: (1) very wet soils across the entire region; (2) large snowpack in the Upper Midwest; and (3) outlooks for a wetter than normal climatological spring season. For those wanting more information related to current hydrologic conditions and/or spring flood outlooks, I have included links to relevant partners and information below.

National Weather Service River Forecast Center: https://www.weather.gov/ncrfc/

NOAA Climate Prediction Center Soil Moisture: https://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/US/Soilmst/Soilmst.shtml

NOAA Climate Prediction Center Seasonal Outlooks: https://www.cpc.ncep.noaa.gov/products/predictions/90day/

A Warm, Wet Start to 2020

Our first month of 2020 was quite a bit warmer and wetter than average across the state. The preliminary statewide average January temperature was 31.4 degrees, 5 degrees above the 30-year normal and the 17th warmest on record going back to 1895. The preliminary statewide average total January precipitation was 4.41 inches, 2.34 inches above the 30-year normal and the 9th wettest on record.

Data are provisional and may change slightly over time

Warm Conditions Persist from 2019

Following a warmer than average December, temperatures remained persistently above average for the first half of January, with only a short cold air incursion between Jan. 15 and 23. January average temperatures ranged from the mid-20s in northern Illinois to the high 30s in southern Illinois, and were 2 to 7 degrees above average across the state.

The majority of January days were warmer than average across the state. For example, the daily mean temperature in Dwight in Livingston County was below the long-term average in only 5 of the 31 January days. Dwight has only experienced 14 days with below average daily mean temperatures since the beginning of meteorological winter on Dec. 1.

Last month, 21 local daily high maximum temperature records and 36 daily high minimum temperature records were broken in Illinois. The highest temperature recorded across the state in January was 65 degrees in Cairo and Carbondale on Jan. 11. Overall, the preliminary January 2020 statewide average was 31.4 degrees, which was the 17th warmest January on record, following the 15th warmest December (2019) on record.

Temperatures since the start of meteorological winter on Dec. 1 are 2 to 7 degrees above the long-term average across the state. As an example, this winter through Feb. 2 is the 4th warmest on record in Moline with an average temperature of 31.1 degrees.  The three winters that were warmer through Feb. 2 in Moline are 2002, 2012, and 2016.

Warmer conditions have helped make for a mild winter so far across the southern half of the Midwest, as indicated by the Accumulated Winter Season Severity Index (AWSSI). AWSSI uses a daily accumulation of points, based largely on temperature, to characterize winter season severity. Despite an early snowfall this season, all AWSSI-monitoring stations in Illinois indicate a mild or moderate winter season so far (see map below). AWSSI data and maps are created by the Midwestern Regional Climate Center (https://mrcc.illinois.edu/research/awssi/indexAwssi.jsp).

A Few Days Make for a Wet January

January total precipitation was above normal across the state, with monthly precipitation totals ranging from 2 inches in northwestern Illinois to nearly 8 inches in south-central Illinois. The highest accumulation was along the Interstate 70 corridor between the St. Louis Metro East and Effingham. This region experienced nearly 300 percent of its average January total precipitation. Vandalia in Fayette County experienced its third wettest January on record with 7.99 inches, over 5 inches above the long-term average. As with most of the wettest parts of the state, Vandalia received 85 percent of its total January precipitation in just three days. Much of this was the result of a single winter storm that moved through the Midwest between Jan. 9 and 12.

Total precipitation between Jan. 10 and 12 broke three-day total January precipitation records at Charleston (5.85 inches), Taylorville (4.35 inches), Champaign (3.63 inches), and Marseilles (3.41 inches). This event resulted in flooding along many of Illinois’ larger rivers, including the Kaskaskia River breaking through the Vandalia levee and causing a temporary closure of highway 51. Rivers crested between 24 and 72 hours after the precipitation ended. As of the end of the month, minor flooding persisted in only the lower Illinois and Kaskaskia Rivers in the state (see map below).

Source: https://www.weather.gov/ncrfc/

Snowfall totals this last month ranged from less than a tenth of an inch in southern Illinois to over 12 inches in northwestern Illinois. There was a strong southeast-to-northwest January snowfall gradient across the state, resulting from a similar gradient in air temperature. The highest January snowfall total was 15 inches in both Stephenson and Bureau Counties. Rockford experienced the highest 1-day snowfall maximum across the state with 6 inches on Jan. 25.

January continued winter season snowfall patterns, with the western third of the state experiencing slightly above normal snowfall since Oct. 1, and the eastern two-thirds of the state experiencing near normal to well below normal snowfall over the same period. A broad area along the Indiana border from Cook County to Lawrence County has experienced between 50 and 75 percent of normal winter season snowfall, whereas most of the state south of Interstate 64 has experienced less than 50 percent of normal snowfall since Oct. 1. In contrast, snowfall totals across a broad area between Jo Daviess County and Madison County in western Illinois has experienced between 100 and 125 percent of normal season snowfall.

As is often the case, Illinois spans the continuum of conditions in the Midwest. Most areas northwest of us have experienced well above normal snowfall where areas to the southeast are in a snowfall deficit. In particular a region spanning the Dakotas to the Upper Peninsula of Michigan have experienced well above normal snowfall this winter season. Two CoCoRaHS stations in the Upper Peninsula have recorded over 210 inches of snowfall since Oct. 1. Heavy snowpack in the Upper Midwest (see map below) can often exacerbate unusually wet conditions in early to mid-spring here in Illinois, especially if a brief warm spell and/or heavy rain causes rapid snowmelt. Therefore Upper Midwest snowpack is an important variable to consider when planning for potential flooding-related impacts in the spring.

Source: https://www.nohrsc.noaa.gov/normals/

Outlooks

Short-term 8–14-day outlooks from the NOAA Climate Prediction Center show strongly elevated odds of above normal precipitation, with the highest probabilities across the southern two-thirds of the state. Short-term temperature outlooks show slightly elevated odds for a continuation of above normal temperatures across the eastern part of the state.

Longer-term 30-day outlooks show elevated odds of both above normal temperature and above normal precipitation in southern Illinois. Seasonal outlooks for spring (March to May) continue to show elevated odds of above normal precipitation across the state, with an equal chance of above normal, normal, and below normal temperatures.

Source: https://www.cpc.ncep.noaa.gov/products/forecasts/

Warm, Dry December Concludes a Cold, Wet Year

December temperatures were well above the long-term average across the state, breaking dozens of local daily maximum and minimum temperature records. The preliminary statewide December average temperature was 35.2 degrees, about 5 degrees above the 1981-2010 normal and the 18th warmest on record. Preliminary data show December was drier than average for most of the state. The statewide average December precipitation total was 2.03 inches, 0.66 inches below the 30-year normal.

Data are provisional and may change slightly over time

Warm Weather

Temperatures during the first half of December were very close to average. This was followed by a brief period of well below average temperatures caused by cold air incursion from the north on the back of a strong upper atmosphere trough to our west. On December 20 the predominant wind direction changed to southwesterly, bringing warm, dry air into the region. Temperatures between December 20 and 29 ranged from 5 to 25 degrees above normal across the state. In total, 104 daily high maximum temperature records and 27 daily high minimum temperature records were broken over this time period, including a few dozen records on December 25. In fact, it was the warmest Christmas day at 68 stations across the state. As shown in the figure below, the daily average temperature in Decatur in Macon County on Christmas was nearly 20 degrees above the 30-year normal.

The station in Elgin (Kane County) broke its previous Christmas day high maximum record by 10 degrees. The highest temperature recorded in the state was 70 degrees on December 26 in Wayne County and again on December 29 in Pope County. The lowest temperature was -4 degrees on December 15 in Rock Island County.

A shift in the upper atmosphere and the passage of a cold front late in the month allowed temperatures to moderate. December average temperatures ranged from the low 30s in northern Illinois to the mid-40s in southern Illinois. Monthly average temperature departures ranged from 7 degrees above the long-term mean in northwestern Illinois to just over 1 degree above average in south-central Illinois.

The preliminary 2019 statewide average December temperature was 35.2 degrees, which was the 18th warmest December on record. December’s warm weather was an aberration in an otherwise colder than average 2019 in Illinois. Only three months this year–July, September, and December–exhibited a statewide average temperature above the 30-year normal.

Precipitation

December precipitation was below the long-term average for the entire state. Areas in far southern Illinois received 2 to 3 inches less than average in December, approximately 50 percent of normal December precipitation. The statewide average total December precipitation was 2.03 inches, approximately 0.66 inches below normal. This last month was the 50th driest December on record in Illinois and marked the second straight month of below average statewide precipitation. Preexisting wetness and reduced evaporative demand, typical for this time of the year, have prevented impacts from the prolonged dry conditions. Despite two straight months of well below average precipitation, streamflow and soil moisture were both near normal across the state.

Snowfall totals this last month ranged from less than a tenth of an inch in far southern Illinois to over 10 inches in south-central Illinois. A strong system came through in mid-December and brought several inches of snow to an area spanning the St. Louis Metro East to the Champaign-Urbana area. The highest 24-hour snowfall total was 5.6 inches in Lovington (Moultrie County) on December 17, although CoCoRaHS observers in Mascoutah in St. Clair County and Columbia in Monroe County both recorded 7.5 inches on December 17.

The December snowfall glut in south-central Illinois turned into snowfall deficits of 8 to 10 inches in northern Illinois. This last month was only the 10th December with 1 inch or less of snowfall in Stockton (Jo Daviess County). Despite the small snowfall totals this last month, the seasonal total snowfall was above average for most of the state between interstates 80 and 64. A broad area between Peoria and the St. Louis metro east received over 4 inches of above average snowfall, whereas the Chicagoland region has so far this season experienced a snowfall deficit of 4 to 6 inches.

Outlooks

Short-term 8-14-day outlooks from the NOAA Climate Prediction Center show strongly elevated odds of both above normal precipitation and above normal temperature.

Thirty-day outlooks show elevated odds of wetter and warmer than normal conditions to persist throughout January in southern Illinois. Outlooks for January through March and March through May continue to show elevated odds of above normal precipitation for the entire state.

Cold November Brings an End to Meteorological Autumn

November temperatures were well below the long-term average across the state, breaking hundreds of local daily records. The preliminary statewide November average temperature was 35.6 degrees, about 7 degrees below our 30-year normal and tied for the ninth coldest on record. Preliminary data suggest November was drier than average for most of the state. The statewide average November precipitation total was 2.51 inches, approximately 0.96 inches below the 30-year normal.

Data are provisional and may change slightly over time

Cold Weather

The intense cold weather at the end of October continued into the first two thirds of November. Average temperatures ranged 10 to 15 degrees below the long-term mean for the first half of the month. Between November 1 and November 15, 149 daily low maximum temperature records and 177 daily low minimum temperature records were broken across the state. Several all-time November temperature records were broken as well, including both the all-time November low minimum and low maximum temperature records in Robinson, Illinois (Crawford County, records back to 1893). At Chicago’s O’Hare airport, 22 out of 30 November days experienced an average temperature below the long-term mean, including the first 19 days of the month. Stations in Knox, Jo Daviess, Carroll, and Whiteside Counties observed daily minimum temperatures below 0 in November, the lowest being -4 degrees in Altona (Knox County) on November 7.

A shift in the upper-atmospheric trough around November 20 allowed temperatures to moderate. Average temperatures between November 16 and November 30 were between 1 and 3 degrees below normal across the state. Overall, November temperatures were between 4 and 8 degrees below the long-term mean across the state. The preliminary 2019 statewide November average temperature was 35.6 degrees, which was also the 2018 statewide average temperature and tied for the ninth warmest November on record.

Precipitation

November precipitation was below the long-term mean for all of Illinois north of Interstate 64. Monthly precipitation totals ranged from 1 to 2 inches in central and northern Illinois to over 6 inches in far southern Illinois. These totals represented between 2 inches below normal and 2 inches above normal.

The statewide average precipitation total for November was 2.51 inches, approximately 1 inch below the 30-year normal and 56th driest monthly total since 1895. November was only the second month this year–along with July–that experienced below normal statewide average precipitation and only the third month since June 2018 (see figure below).

Despite the dryness, abundant October precipitation and timely rain and snow events throughout November alleviated all abnormally dry conditions across the state. According to the U.S. Drought Monitor, the entire state has been free of drought and abnormally dry conditions since November 5.

Although total precipitation was below normal for most of the state this last month, snowfall totals were well above average. Total November snowfall accumulations ranged from nearly 12 inches in northern Illinois to just over half an inch in far southern Illinois. Accumulations were between 1 and 6 inches below the long-term November average snowfall totals. Measurable snowfall (accumulation greater than 0.10 inches) occurred in November as far south as Cairo (Alexander County). The highest November snowfall total was 11.7 inches in McHenry County.

Just as impressive as the snowfall totals this month was the number of days with measurable snowfall. The long-term weather station in Freeport recorded 5 days in November with measurable snowfall, tied for the second most since 1948 and the most since 1978.

December Outlooks

Both short-term 8- to 14-day outlooks and 1-month December outlooks from the Climate Prediction center show strongly elevated odds of above normal temperatures across the state. The outlooks are informed in part by predicted changes in mid-level atmospheric pressure patterns in early December, which permit southerly movement of warm air into the region.

The shorter and longer outlooks both show slightly elevated odds of above normal precipitation, although odds are weaker than for temperature outlooks. Winter (December–February) outlooks show an equal chance for temperature and slightly elevated odds for above normal winter precipitation.

October: Heat to Snow

We saw highly variable temperatures across the state this month, with record-breaking heat in the early part of October, and record-breaking cold in the latter part. The preliminary statewide October average temperature was 53.7 degrees, less than 1 degree below our 30-year normal. Temperatures were near normal in eastern Illinois, and between 2 and 6 degrees below normal across western Illinois. Preliminary data suggest October was considerably wetter than normal for the entire state. The statewide average October precipitation total was 5.20 inches, approximately 2 inches above the 30-year normal. The wet deviations were particularly large in the northern and southern reaches of the state.

Data are provisional and may change slightly over time

Temperature Variability

Record-breaking high temperatures persisted from September into early October. Average temperatures during the first four days of October were 10 to 14 degrees above normal in the southeast part of the state, and 3 to 8 degrees above normal for the northwest part (see map below). Maximum temperatures broke 90 degrees and minimum temperatures remained in the 70s for several days in southern Illinois. Stations in Saint Clair and White Counties reached 96 degrees on October 2.  Between October 1 and October 4, 46 daily high maximum temperature records and 73 daily high minimum temperature records were broken across Illinois, according to the NOAA National Centers for Environmental Information (NCEI). Additionally, 9 stations broke their all-time October high maximum temperature records, and 13 stations broke their all-time October high minimum temperature records. In one particularly extreme event, the October 1 nighttime minimum temperature at Kaskaskia Lock and Dam in Randolph County was 72 degrees, 10 degrees above the previous daily record and 2 degrees above the all-time October minimum temperature record at that station.

Seasonable temperatures ensued after the heat was broken toward the end of the first week of October. Temperatures from October 5 to October 27 were near normal in eastern Illinois and between 3 and 6 degrees below normal for western Illinois (see map below). Nearly all the state experienced the first fall frost event in the second week of October. Nighttime minimum temperatures dipped below 32 degrees as far south as Pope County and below 28 degrees in Warren and Jo Daviess Counties.

The heat wave that started the month was matched by a strong burst of cold air to close out the month. Temperatures between October 28 and October 31 were 8 to 16 degrees below normal. Similarly, 48 daily low maximum temperature records and 12 daily low minimum temperature records were broken across Illinois over the last four days of the month. Nighttime minimum temperatures dropped below 30 degrees as far south as Pulaski County. The lowest minimum temperature observed in October was 14 degrees in both Carroll and Lee Counties on Halloween night. Halloween was also the coldest on record for 51 stations across Illinois.

The temperature contrast between the start and end of this month may be best summarized in the graph below, which shows daily maximum and minimum temperatures at Springfield Abraham Lincoln Capital Airport this last month. There was a 57° difference between daily maximum temperatures on October 1st and October 31st in Springfield, both of which broke daily records. In fact, 10 Illinois COOP stations broke their daily high maximum temperature record on October 1st and their daily low maximum temperature record on October 31st.

Precipitation

October precipitation was above normal for virtually all of Illinois. The statewide total precipitation in October was 5.20 inches, approximately 2 inches more than the 30-year normal. Areas of far northern and southern Illinois received over 7 inches of rainfall in October. CoCoRaHS observers in New Lenox in Will County and Riverwoods in Lake County recorded over 12 inches of precipitation in October. Expressed as a percent of the long-term mean, areas of northeastern Illinois received more than 200 percent of mean October precipitation, and a broad swath of southern Illinois received over 150 percent of mean October precipitation (see maps below). Significant rainfall helped improve drought conditions in southern Illinois. The latest U.S. Drought Monitor map – current as of October 29 – shows no drought in Illinois for the first time since early August.

The cool down that came at the end of this month brought a variety of precipitation, including snowfall and some snow accumulation in northern and western Illinois. Total snowfall accumulation over the last week of October ranged from over 8 inches in northwestern Illinois to just over a tenth of an inch as far south as Nokomis in Montgomery County. The highest October snowfall total, 8.5 inches, was in Orangeville in Stephenson County. Although late October is early for the first snowfall in Illinois, it is certainly precedented. The map below shows the date of the earliest recorded snowfall (> 0.1 inch) at COOP stations across the state.

Short- and Long-Term Outlooks

Short-term 8- to 14-day outlooks from the Climate Prediction Center show strongly elevated odds of below normal temperatures persisting into the first couple of weeks of November. Concurrently, probabilities are elevated for below normal precipitation out to 14 days, as drier weather is likely to prevail following the first winter storm of the season in Illinois.

Longer-term outlooks for November also show increased odds of below normal temperatures and increased odds of above below normal precipitation. Winter (December–February) outlooks show greater odds of a wetter than normal winter.

 

September Heat, Flooding, & Drought

This past month was tied for the 4th warmest September for Illinois (state average temperatures back to 1895), and the warmest September since 1933. Precipitation varied tremendously from north to south across the state.

Preliminary data suggest that September was tied for the 4th warmest on record for Illinois. The preliminary average statewide September temperature was 71.3 degrees, which is 4.9 degrees above the long-term average. Monthly temperatures ranged from 2 to 4 degrees warmer than normal in northeast Illinois to over 6 degrees warmer than normal in southwest Illinois. The preliminary average statewide precipitation was 5.34 inches, which is 1.9 inches above the long-term September average. However, the data also show large differences in September precipitation totals across the state, with northern Illinois receiving much more than average precipitation, and southern Illinois receiving much less than average.

Data are provisional and may change slightly over time. 

Precipitation, Flooding, & Drought

September precipitation totals reveal a strong north-to-south gradient. Areas of northern and north-central Illinois received in excess of 12 inches of rainfall in September, while areas of southeast Illinois received less than 0.25 inches over the same time period (see maps below). Expressed as a percent of normal September precipitation, these totals ranged from 300 percent of normal in northern Illinois to less than 5 percent of normal in southeast Illinois. Locally, a station near Stockton (Jo Daviess County) observed 16.62 inches in September (nearly 13 inches more than normal), while the station at Smithland Lock & Dam (Pope County) recorded only 0.02 inches (3.5 inches less than normal).

August 2019 was the first months since September 2018 during which the U.S. Drought Monitor identified drought in the state. In September, dryness in east-central Illinois persisted but did not intensify. The latest U.S. Drought Monitor map (September 24) shows a pocket of moderate drought covering parts of Champaign, Ford, Iroquois, and Vermilion counties (see map below). Concurrently, below normal rainfall and above normal temperatures in the southern part of the state produced dryness in September. The latest U.S. Drought Monitor depicts abnormally dry conditions for most of Illinois south of I-64, and a pocket of moderate drought from Pope and Hardin counties in the southeast to Perry and Franklin counties in south-central Illinois. Conditions in southern Illinois have shown some signals of a flash drought, which is a rapidly intensifying drought event, often provoked by existing precipitation deficit combined with intense heat.

Reports from Illinois Farm Bureau CropWatchers regarding drought in east-central and southern Illinois are mixed. Some report the dryness and heat have helped late-planted crops reach maturity, while at the same time possibly sacrificing yield. The recent National Weather Service 7-day precipitation forecast calls for 1 to 4 inches of rain in the northern half of the state, with 7-day forecasted totals less than 0.5 inches in southern Illinois (see map below).

In contrast to the ongoing drought in southern and east-central Illinois, September was abnormally wet for most of northern and north-central Illinois. Persistent, heavy rains led to flooding impacts in parts of northern Illinois, including the closure of several state parks and significant flooding along the Fox and Des Plaines Rivers, among others. Areas in northern and north-central Illinois received in excess of 12 inches of rainfall in September. In most parts of Peoria, Woodford, Marshall, and Livingston Counties, most of the rainfall totals came in a 24-hour period between September 27 and 28. This event created dangerous flash flooding from Peoria into the southwest Chicago suburbs.

The COOP station in Minonk, Illinois (Woodford County) recorded 9.09 inches of rainfall over that 24-hour period, although that likely fell over a less than 12-hour window. This total approached the 24-hour, 500-year storm total of 9.53 inches and surpassed the 12-hour, 500-year storm total of 8.29 inches. A 500-year storm total refers to a precipitation accumulation over a given time period (e.g., 12, 24, 48 hours, etc.) and has a 0.2 percent chance of occurring in a given year. Impressively, the 9.09-inch total in Minonk broke, and nearly doubled, the all-time 24-hour precipitation total record at that station, which was just over 5 inches (data going back to 1895). Images of flooded fields in Woodford and Marshall Counties suggest this most recent heavy precipitation event may delay harvest.

Temperature

 

The September temperature was much more consistent across the state than precipitation, as the entire state experienced above normal temperatures this month (see maps below). Apart from the last full week in September, most of the state has been under the influence of a large high-pressure system this month, centered to our southeast. This system has allowed warm air to intrude from the south/southwest, generating warmer than normal conditions for this time of the year. In fact, the statewide September average temperature was 71.3 degrees, tying it for the 4th warmest September on record in Illinois (back to 1895). September average temperatures across the state ranged from 65 degrees in Jo Daviess County to 78 degrees in Lawrence County. The lowest minimum temperature reported in Illinois in September was 45 degrees in Jo Daviess County on September 5, and the highest maximum temperature reported in Illinois was 97 degrees in both Alexander and Pope Counties on September 16. Well over 100 local daily climate records were broken in Illinois in September, most of which were high daily minimum temperature records. This is attributed to several very warm nights, including the night of September 22, when the nighttime minimum temperature remained above 70 degrees as far north as Elizabeth (Jo Daviess County) and Freeport (Stephenson County). On the night of September 10, the station in Rock Island reported a nighttime minimum temperature of 77 degrees, besting the previous daily record by 3 degrees.

Short-term temperature forecasts call for continued above average temperatures for the first few days of October and then a regression to cooler, more seasonal conditions. Longer term Climate Forecast System (CFS) forecasts from the National Centers for Environmental Protection show probabilities of a 32-degree freeze in Illinois remain below 30 percent into the third week of October. The map below shows the probability of a daily minimum temperature below 32 degrees between October 14th and October 21st.

October 2019 Outlook

 

Looking into October, the 8 to14-day outlook from the Climate Prediction Center (CPC) shows elevated probabilities of above normal temperatures and elevated probabilities of above normal precipitation across the state.

The CPC monthly outlook for October still shows elevated probabilities for below normal temperatures across the northern half of the state, with equal chances (above normal, normal, below normal precipitation) for all but the very northwest corner of Illinois (see maps below).

 

Illinois First Fall Freeze Climatology

Due to significant planting delays across most of the Midwest this year, I have heard many concerns about an early fall freeze and its potential effects on immature crops. Most plants experience damage from a hard freeze or “killing freeze”, which is typically designated by a daily minimum air temperature at or below 28°F. Even in normal growing seasons, an early fall freeze can cause considerable impacts and yield losses for crops. Delayed planting, as was the case this season, increases the risk of freeze damage because crops are less mature going into our normal fall freeze time.

The maps and summary below show first fall freeze dates across Illinois using temperature observations over the period 1979 to 2018. The maps show the earliest and latest fall freeze dates over this 40-year period, as well as the median date, which represents the middle value in the range of dates. The median is preferred over the mean or average, as it is less sensitive to very early or very late freeze dates. Also shown are the 10th (1 in 10 years) and 90th (9 in 10 years) fall freeze dates. All station temperature data were provided by the Midwest Regional Climate Center (https://mrcc.illinois.edu); the shaded areas between stations on the map were interpolated and do not represent actual observations.

The earliest fall freeze dates over the past 40 years range from late September in northwest and central Illinois, to early October in southern and eastern Illinois. An early freeze anomaly can be seen at the Mt. Carroll station (Carroll County), which experienced a minimum temperature of 27°F on September 7, 1988. Interestingly, the observed all-season Illinois minimum temperature record was broken earlier this year at the Mt. Carroll station (-38°F).

Tenth percentile first fall freeze dates (i.e., 1 in 10 years) range from early October in northwest and central Illinois to mid- to late October in southern and eastern Illinois.

Median first fall freeze dates range from mid- to late October in northwest and central Illinois to late October/early November in southern and northeastern Illinois. Approximately half the years between 1979 and 2018 experienced the first fall freeze before the median dates. Also, the median dates map clearly shows the effects of the developed Chicagoland area on nighttime minimum temperatures. The median first fall freeze date at Chicago Midway is 10 to 15 days later than in some of the collar counties.

Ninetieth percentile first fall freeze dates (i.e., 9 in 10 years) range from early November in northwest and central Illinois to mid- to late November in southern Illinois. Based on the 40-year climatology, one could say that there is a 90% chance that the first fall freeze on any given year will occur on or before the dates in the 90th percentile map.

Finally, the latest first fall freeze dates across the state range from mid- to late November in northwest Illinois to early to mid-December in southern Illinois.

Note that air temperatures can vary considerably on smaller or micro-scales. For example, plants near heated buildings or other development can be spared when minimum temperatures dip below the 28°F threshold in the countryside. More information and useful freeze products are provided by the Midwestern Regional Climate Center as part of their Vegetation Impact Program (https://mrcc.illinois.edu/VIP/indexFFG.html).  Higher quality, full-page maps can be accessed by clicking the following links:

10th_Percentile 90th_Percentile Earliest Latest Median

Unequal August Precipitation Leads to Drought in Illinois

August 2019 will be remembered for remarkable differences in monthly precipitation totals across Illinois, as well as the first appearance of drought in the state since September 2018.

It would be inappropriate to summarize August 2019 precipitation across the state using only one adjective. Preliminary data suggest that August was drier than average across much of the state north of I-72 and south of I-64, while much wetter than average conditions prevailed between the two interstates. The preliminary average statewide precipitation was 4.21 inches, which is 0.61 inches below the long-term August average. The preliminary average statewide August temperature was 72.8 degrees, which is 0.7 degrees below the long-term average.

Data are provisional and may change slightly over time

Precipitation & Drought

July 2019 was the first month since November 2018 that ended with below average statewide precipitation. Dryness in the northwest and east-central parts of the state that began in July persisted in August.

Areas in the south-central part of the state, particularly in the western extent of the St. Louis metro east, have received precipitation totals in August between 5 inches and 8 inches above normal, with a station near Patoka (Marion County) reporting the highest August rainfall total of 14.19 inches. Most areas of the state north of I-72 and south of I-64, in contrast, received below normal rainfall in August, in some cases up to 4 inches below normal. The driest area in August covered parts of Ford, Iroquois, and Vermilion counties in east-central Illinois, where precipitation totals were less than 50 percent of their August normal (see maps below).

 

The continued dry conditions from July to August led the U.S. Drought Monitor to identify moderate drought (D1) in northwest and east-central Illinois in their August 13 map. This was the first time the Drought Monitor identified drought in Illinois since September 2018, which represents the largest number of consecutive, drought-free weeks (48) since the Drought Monitor began 20 years ago. The latest Drought Monitor map, from August 29, shows moderate drought persistence in northwest and east-central Illinois (see figure below).

The combination of late planting, due to flooding, and multi-week drought has stressed crops and farmers across central Illinois. Reports from Illinois Farm Bureau CropWatchers discuss corn dropping ears and beans dropping leaves in parts of Champaign County. The recent National Weather Service precipitation forecast calls for between 0.75 inches and 2 inches over the next 7 days for most of the northern half of the state, with little to no precipitation in southern Illinois.

Temperature

Much of the state experienced near normal to slightly below normal temperatures in August. A strong cold front in the early part of the month and the last week of the month resulted in cooler conditions, with minimum temperatures ranging from the high 40s to high 50s across the state. This was particularly the case for the northwest quadrant of Illinois. However, all of the state experienced August temperatures within 2 degrees of the long-term August mean (see maps below). August average temperatures ranged from 79 degrees in Pulaski County to 68 degrees in Jo Davies County. The lowest minimum temperature reported in Illinois in August was 48 degrees in DeKalb County on August 2nd, and the highest maximum temperature reported in Illinois was 98 degrees in Pulaski County on August 20th.

September 2019 Outlook

Looking into September, the monthly outlook from the Climate Prediction Center (CPC) issued on August 31 shows slightly elevated probabilities of below normal temperatures across the northern half of the state, with equal chances of above normal, normal, and below normal temperatures in the southern half.

September precipitation probabilities slightly favor above normal precipitation in the northwest corner of the state, but are equal (above normal, normal, below normal) for the rest of Illinois (see maps below).

September 2019 Temperature Outlook

September 2019 Precipitation Outlook