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. 

 

May 2019: Exceptionally Wet and Stormy Across Illinois

May 2019 will be a month remembered for exceptional, record-breaking wet conditions locally, as well as an active, stormy, and at times severe weather pattern across the state.

Preliminary data suggest that May 2019 finished significantly wetter than average, with temperatures marginally below the long-term average. The preliminary average statewide May temperature was 62.5°F, which is 0.2°F below the long-term average. The preliminary average statewide precipitation was 8.43 inches, which is 3.83 inches above the long-term average.

Precipitation

Preliminary statewide average precipitation for May was 8.43 inches, which is 3.83 inches above the long-term average, marking six consecutive months with above average statewide precipitation. As it stands now, spring 2019 will rank within the top four wettest spring seasons in state history (March–May), with May 2019 ranking as the third wettest May in state history.

The multi-sensor precipitation departure map for Illinois shows that practically the entire state received above average precipitation for the month. The only exception was a small region in east-central Illinois near Edgar County, where near to slightly below average precipitation occurred (see maps below).

Portions of west-central and northern Illinois reported the heaviest rainfall for the month, where monthly precipitation departures of 5 to 8 inches above average were common, bringing 200 to 300 percent of average monthly rainfall.  An area roughly defined between Quincy and the Quad Cities extending eastward to near Peoria received the most precipitation in the state, with 7 rain gages in this region recording 13 or more inches of rainfall during May.

A gage near Dallas City (Hancock County) reported the highest precipitation total for May, with an impressive 14.75 inches.

Data from the National Weather Service showed that with a report of 8.25 inches, Chicago experienced its wettest May on record, beating the 8.21-inch reading that was set just last year in May 2018.

The abnormally wet May weather has led to a continuation of elevated flooding risks and significant planting delays for the Illinois agricultural community.  Moderate and major flooding along many local streams and rivers is still ongoing, with flood warnings along both the Illinois and Mississippi Rivers in effect until further notice.

Wet, active, and stormy weather has not only been an issue for Illinois, but also the weather has been a growing risk across much of the central and southern Midwest including the Corn Belt where notable above average precipitation departures for May were also present (see map below).

Severe Weather

In addition to the relentless rainfall, multiple rounds of severe weather impacted the state throughout the month. Statewide, 218 severe weather reports were noted from the Storm Prediction Center, 20 for tornadoes (red), 52 for hail (green), and 146 for wind (blue). Note that multiple reports may be generated for a single event.

Map of May 2019 Severe Weather Reports in Illinois, updated 6/4/2019

Temperature

Preliminary results show that May 2019 finished with a statewide average temperature of 62.5°F, which is 0.2°F below the long-term average.

Monthly temperature departures showed that the northern third of the state generally saw average temperatures of 1 to 3 degrees below normal, while the southern third of the state generally saw average temperatures of 1 to 3 degrees above normal, with near normal temperatures occurring throughout central Illinois.

The highest maximum temperature in the state was recorded at the Kaskaskia River Navigation Lock (Randolph County) with a reading of 93°F on May 26. In contrast, the lowest minimum temperature of 31°F was recorded at the Chicago Botanical Garden (Cook County) on May 4.

June 2019

Although an active weather pattern looks to continue at least for a portion of the first full week of June, the monthly outlook from the Climate Prediction Center favors equal probabilities for below, near, or above average precipitation and temperatures across Illinois for June 2019.

Rainfall Over the Last 2 Weeks in Illinois

 
Here are the amounts for the last week, as of this morning. The areas in purple in far southern Illinois have received between 10 and 15 inches. Areas in shades of red have received between 5 and 10 inches. The areas in orange and yellow have received between 2 and 5 inches. Areas in green in northwest IL have received between  0.5 and 2 inches.
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Here are the rainfall totals for the past two weeks. Same color scheme as before. Notice how the areas with 10 to 15 inches have expanded across much of southern IL south of Interstate 64 with a few areas just to the north.
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NWS Cooperative Observer Network rainfall totals in Illinois for the period of April 26 to May 5, 2017, ranked from high to low. Totals that have exceeded the expected 10-day, 100-year rainfall amounts for that area are in red. Continue reading “Rainfall Over the Last 2 Weeks in Illinois”

Wet April and 2nd Warmest January-April on Record for Illinois

Precipitation: The statewide average precipitation for April in Illinois was 7.01 inches, 3.23 inches above normal and the 2nd wettest April on record. Here are the top five wettest Aprils. Notice a pattern? Three out of the five have been since 2011.

  1. April 2011 – 7.62 inches
  2. April 2017 – 7.01 inches
  3. April 1957 – 6.99 inches
  4. April 2013 – 6.93 inches
  5. April 1927 – 6.87 inches

The largest monthly total for April in Illinois was Carbondale with 14.41 inches. Several other sites in southern Illinois had similar amounts including Bush (Williamson County) with 13.63 inches, West Frankfort (Franklin County) with 13.35 inches, Kaskaskia (Randolph County) with 13.34 inches, and Murphysboro (Jackson County) with 13.02 inches.
Temperature: The statewide average temperature for April was 56.4 degrees, 3.8 degrees above average and the 11th warmest April on record. The warmest reading for April was 89 degrees at Kaskaskia on April 20.  The coldest reading for the month was 19 degrees at Morrison on April 10.
Statewide records of temperature and precipitation go back to 1895.

Graphs

Here are the temperature departures for 2017. As you can see, every month in 2017 has been well above normal. So far this January-April is the 2nd warmest such period on record with a statewide average temperature of 43.2 degrees, 5.4 degrees above normal. Only 2012 was warmer at 44.5 degrees, 6.7 degrees above normal. [corrected from an earlier version]
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Continue reading “Wet April and 2nd Warmest January-April on Record for Illinois”

Widespread, heavy rains possible over next week in Illinois

As of April 25, the statewide average precipitation for Illinois is 2.8 inches, which is 94% of normal. However, we have several opportunities for widespread rains this week and into the weekend, according to the NWS precipitation forecast.
The first round of rain on Wednesday and Thursday has potential rainfall amounts of 1 to 2 inches across most of Illinois, along with the chance for severe weather. Continue reading “Widespread, heavy rains possible over next week in Illinois”

National Climate Assessment for Illinois

Earlier this year the National Climate Assessment for Illinois was released, tracking the historical changes in temperatures and precipitation in Illinois. You can find the full report for Illinois and other states at the State Climate Summaries website.
Here is Key Message #1

Average annual temperature has increased by about 1°F since the beginning of the 20th century. There has been seasonal variation in this warming, with average spring temperature increasing by about 2°F and average summer
temperature increasing very little. Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century.

Key Message #2

Precipitation in spring and summer has generally been above average over the past two decades, affecting agriculture in both positive (adequate soil moisture) and negative (delays in spring planting) ways. Precipitation in winter and spring is projected to increase, which poses a continuing risk of spring planting delays.

Key Message #3

Severe flooding and drought have occurred periodically in recent years. Future increases in extreme precipitation events and in evaporation rates may increase the intensity of both floods and droughts.

You may notice that two out of the three messages relate to increases in precipitation and especially heavy rainfall events. The graphic I found most compelling was this one for the increasing number of 2-inch rain events with time. The caption explains how this graph was created. The increased frequency in 2-inch rain events seen since the early 1980s lines up very well with my experience and research over the years in Illinois.

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Figure 5: The observed number of days with extreme precipitation events (annual number of days with precipitation greater than 2 inches) for 1900–2014, averaged over 5-year periods; these values are averages from 43 available long-term reporting stations. A typical station experiences 1–2 such events each year. The number of extreme precipitation events has been above average since the 1990s. During the most recent 5-year period (2010–2014), Illinois experienced a record high number of events when stations averaged more than 2 events annually. The dark horizontal line is the long-term average (1900–2014) of 1.62 days per year. Source: CICS-NC and NOAA NCEI.

Continue reading “National Climate Assessment for Illinois”

Wet August in Illinois

As of yesterday, the statewide average rainfall was 4.47 inches. That is already 0.9 inches above normal for the month and the 27th wettest August on record (since 1895). The wettest August on record was 1977 with 6.86 inches. The latest NWS forecast is showing the potential for another inch of rain to fall in the next 7 days (last map). That would put us in the top ten wettest Augusts on record.
The highest rainfall total in the state for August is Waltonville (Jefferson County, in southern Illinois) with 13.43 inches. A CoCoRaHS station just 3 miles away reported 12.94 inches (IL-JF-2).
Here are the rainfall totals through the morning of August 19 (left) and the departure from normal (right). The heaviest amounts have been in southern Illinois with 6 to 10 inches pretty common. Most of the state is well above normal on rainfall except for a spot in western Illinois and several counties in northeast Illinois. Click to enlarge.


Continue reading “Wet August in Illinois”

5-Day Rainfall in Illinois and Midwest

Here are the 5-day accumulated rainfall totals for Illinois and the Midwest. Rainfall was heaviest south of Interstate 70 where amounts of 4 to 8 inches were common (lighter shades of blue). The largest 5-day rainfall total was from a CoCoRaHS station at Waltonville (IL-JF-2) with 10.79 inches. CoCoRaHS is a national network of trained volunteer precipitation observers, learn more at cocorahs.org
Continue reading “5-Day Rainfall in Illinois and Midwest”

100-Year Storm Strikes Illinois State Fair

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Radar-estimated rainfall from August 12 storm.

The 5.59 inches of rain reported at the Springfield Airport on Friday night fell in 6 hours. This represents the 100-year storm for that duration in central Illinois, according to Bulletin 70. The results were dramatic, as reported by the Springfield Journal Register.
The concept of the 100 year storm is commonly used by engineers for assessing the risk of heavy rainfall. The 100-year storm is more completely described as the storm expected to have a return period of once every 100 years on average. The phrase “on average” being key. It does not mean the storms are exactly 100 years apart. Instead it means that if you look at rainfall statistics long enough the average frequency of such a storm would be 100 years. Unfortunately, we don’t have hundreds of years of rainfall data. Instead we estimate the values based on fitting a statistical model to the observed data.
While the phrase “100-year storm” is eye catching, it does not do a good job conveying the risk of such an event. A better way of describing it would be the “1% chance storm”, Continue reading “100-Year Storm Strikes Illinois State Fair”

Heavy Rains on August 12-15

As forecasted by the National Weather Service, heavy rains have fallen across Illinois since Friday. Here are the totals by day and for the three days combined. More rain is expected today and tomorrow (last map). Friday’s rainfall is shown on the 24-hour totals for the morning of August 13, etc. We have had a stationary front parked over Illinois since Friday, which is usually a key ingredient for getting significant rainfall amount.
Here is the set of maps showing the rainfall totals for each day, using rain-gage calibrated rainfall totals. It provides a higher level of details with fairly good accuracy. The downside is that the color scale changes slightly from map to map.

Rainfall totals for the morning of August 13, 2016

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Morning of August 13, 2016.

Rainfall totals for the morning of August 14, 2016

Continue reading “Heavy Rains on August 12-15”