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.

June – Warmer and Wetter in Illinois, More to Follow

Summary: The statewide average temperature for June so far is 75.3 degrees, 4.4 degrees above normal. The statewide average precipitation for June is 3.61 inches, which is about 130% above normal. However, the precipitation is spread unevenly throughout the state. Above-normal temperatures are expected to continue for July.
Temperature: Both the average high and average low for June has been above normal (maps below). The average high ranged from the low 90s around St. Louis to the upper 80s in the southern two-thirds of Illinois. The average high ranged from the upper 70s to the low 80s in the northern third of the state. The average lows ranged from the upper 50s in northeast Illinois to the 60s for the rest of the state.


Precipitation: Precipitation was highly variable across Illinois, which is fairly typical for summer months (below). There are a few areas in pink with 10 to 15 inches. Areas in shades of orange and red have precipitation amounts of 4 to 10 inches, well above normal. The largest monthly total so far is Beecher City (Effingham County) with 11.22 inches. Meanwhile, rainfall has been less plentiful in western and southern Illinois with amounts of 2 inches or less. Continue reading “June – Warmer and Wetter in Illinois, More to Follow”

Outlook for Spring and Summer from NWS

The new outlooks for March, Spring, and Summer from the National Weather Service’s Climate Prediction Center are out.  You can click on any map to see the larger version.
Overview: The NWS says that La Nina conditions continued through January and into early February across the equatorial Pacific Ocean, as indicated by oceanic and atmospheric observations. The CPC/IRI consensus ENSO forecast indicates that La Nina conditions are expected to decay rapidly and transition to ENSO-neutral conditions during Spring. ENSO-neutral conditions are favored to persist through at least the summer.

March

Parts of Illinois shaded in blue have an increased chance of colder than normal conditions. This is part of a larger area of expected colder conditions that extend from the Midwest westward and is a classic La Nina signal for this region. Current climate conditions do not favor colder or warmer than normal conditions in the rest of Illinois. Current climate conditions do not favor wetter or drier than normal conditions in Illinois in March.

March-April-May

Continue reading “Outlook for Spring and Summer from NWS”

Outlook for Spring and Summer from NWS

The new outlooks for March, Spring, and Summer from the National Weather Service’s Climate Prediction Center are out.  You can click on any map to see the larger version.
Overview: The NWS says that La Nina conditions continued through January and into early February across the equatorial Pacific Ocean, as indicated by oceanic and atmospheric observations. The CPC/IRI consensus ENSO forecast indicates that La Nina conditions are expected to decay rapidly and transition to ENSO-neutral conditions during Spring. ENSO-neutral conditions are favored to persist through at least the summer.

March

Parts of Illinois shaded in blue have an increased chance of colder than normal conditions. This is part of a larger area of expected colder conditions that extend from the Midwest westward and is a classic La Nina signal for this region. Current climate conditions do not favor colder or warmer than normal conditions in the rest of Illinois. Current climate conditions do not favor wetter or drier than normal conditions in Illinois in March.

March-April-May

Continue reading “Outlook for Spring and Summer from NWS”

NWS Outlook for First Half of 2018

The NWS released their new outlooks for the first half of 2018. First of all, the NWS notes that La Niña conditions continue across the Pacific Ocean and will likely persist through the rest of winter. It will likely fade this spring, leading to so-called “ENSO-neutral” conditions, which will continue through summer. “ENSO-neutral” just means that we are between La Niña and El Niño conditions, in other words, neutral.

January

The shorter-range forecasts out to 14 days indicate a shift in the weather pattern bringing warmer and wetter than normal conditions across Illinois. By this Sunday we could be in the 40s and 50s in Illinois (left panel, below) while the prospects of rainfall are high with potential totals of 1/2 to 1 inch over the next 7 days (right panel).


Continue reading “NWS Outlook for First Half of 2018”

NWS Outlook for First Half of 2018

The NWS released their new outlooks for the first half of 2018. First of all, the NWS notes that La Niña conditions continue across the Pacific Ocean and will likely persist through the rest of winter. It will likely fade this spring, leading to so-called “ENSO-neutral” conditions, which will continue through summer. “ENSO-neutral” just means that we are between La Niña and El Niño conditions, in other words, neutral.

January

The shorter-range forecasts out to 14 days indicate a shift in the weather pattern bringing warmer and wetter than normal conditions across Illinois. By this Sunday we could be in the 40s and 50s in Illinois (left panel, below) while the prospects of rainfall are high with potential totals of 1/2 to 1 inch over the next 7 days (right panel).


Continue reading “NWS Outlook for First Half of 2018”

Outlook for Summer, Above Normal Temps

The NWS released their outlooks for the month of July and the 3-month period of July-September.
Illinois and much of the US has an increased chance of warmer-than-normal temperatures for both July and July-September (first column in the figure). Illinois has equal chances of being above, below, and near-normal on rainfall – a virtual coin toss. That is not a surprise on the rainfall. Most of our summertime rain is guided by local conditions and fast-changing weather patterns.
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Historical Trends for July
Temperatures: Historically in Illinois, daytime temperatures in July have become milder over time (first graph) while nighttime temperatures have become warmer over time (second graph). While the decreased heating during the day may be welcome, the increased warming at night can be problematic for humans, animals, and plants as they rest. The green line is a smoothed curve to help the eye see the underlying pattern of change from the variability of individual years. Continue reading “Outlook for Summer, Above Normal Temps”

Above-Average Temperatures Expected to Continue through Fall

The NWS released their latest forecasts for May and beyond. Currently, the Pacific Ocean is in the neutral phase between La Niña and El Niño. There is much debate on if and when El Niño should return. It could happen in late summer.  Meanwhile, the theme running through the outlooks is the increased risk of above-average temperatures through the fall. Illinois has been running warmer than average in the last few years. In 2016, 10 out of 12 months were above-average. So far, every month in 2017 has been above-average.

  • January 2017: 5.7 degrees above average
  • February 2017: 10.1 degrees above average
  • March 2017: 1.9 degrees above average
  • April 1-19, 2017: 6.5 degrees above average

May: eastern portions of Illinois have a slightly increased chance of being warmer than average. I am going out a little farther on the limb and say that all of Illinois has an increased chance of being warmer than average, based on recent trends and the climate models. Meanwhile, most of Illinois and the Great Lakes are expected to have an increased chance of below-average precipitation. Click to enlarge maps. Continue reading “Above-Average Temperatures Expected to Continue through Fall”

Outlook for March, Spring, and Summer

The National Weather Service just released their outlook for March and spring. We have moved out of the La Niña pattern in the Pacific pattern to something called ENSO-neutral conditions this spring.That means we are between the El Niño and La Niña phases in the Pacific Ocean. Some of the predictive models are indicating a shift towards a weak El Niño by summer. That is actually good news for Illinois since we have a tendency to experience milder summer temperatures under those situations.
For March, they have Illinois in a region called “EC”, meaning that we have equal chances of being above, below, or near-normal on temperature and precipitation. Sometimes I call “EC” a neutral forecast because it does not lean one way or another.
For March-May, Illinois has an increased chance of above-normal temperatures and northern Illinois has an increased chance of above-normal precipitation.
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Continue reading “Outlook for March, Spring, and Summer”

November Trending Warmer, Wetter

Based on historical data for Illinois, the weather in November is trending towards warmer and wetter conditions over time. Based on the latest NWS forecasts, this November is likely to continue that pattern.

Historical Trends

Temperature

The statewide average temperature for November shows a wide variation from year to year – typical of all months in Illinois. However, there is an underlying warming trend of about 2 degrees over the last century.

nov-temp
Temperature

Precipitation

Continue reading “November Trending Warmer, Wetter”