Warmest May on Record for Illinois

Temperatures: Based on preliminary data, the statewide average temperature for May in Illinois was 70.6 degrees, 7.9 degrees above normal and the warmest May on record. The old record was 69.4 degrees set back in 1962. A brief examination of daily records indicates that Springfield, Champaign, Quincy, and Carbondale all had daily mean temperatures at or above normal for each day of the month. On the other hand, Chicago, Rockford, and Peoria had a few dips into the below-normal territory but overall finished above-normal for the month. Here is the graph of daily mean temperature departures from normal for Champaign-Urbana.


“Normal” refers to the standard 1981-2010 average. For daily normals, additional smoothing is done since even a 30-year average can have some variability from one day to the next.

It was not just warm in Illinois. Here are the temperature departures from normal across the US for the month of May.


Precipitation: Based on preliminary data, the statewide average precipitation for Illinois in May was 3.98 inches, 0.62 inches below normal. Here are the monthly totals and departures from normal maps for Illinois. Click to enlarge. Areas in northern and southwestern Illinois received sizable rainfall amounts. Meanwhile, a few spots in east-central and southeastern Illinois were well below normal, and a cause for concern as we move into the summer months. The highest monthly total reported in the state was at Barrington (Cook County) with 12.69 inches. On the other hand, Effingham reported one of the lower totals in the state with 1.11 inches.

One of the key rainfall producing systems in Illinois in May was when the remains of Subtropical Storm Alberto tracked up the IL-IN  border. As noted in a previous post, the remains of tropical storms have reached Illinois in the past.


Forecast: The National Weather Service’s Climate Prediction Center released their updated outlook for June. For Illinois, we have a greater chance of seeing the above-normal temperatures continue in June. The area around Chicago has an increased chance of below-normal rainfall, which may be welcome after the wet May. The 6-10 and 8-14 days forecasts are showing Illinois with an increased chance of both warmer and drier than normal conditions for the first half of June.



Illinois to Feel Effects of Alberto

According to the National Hurricane Center, what’s left of Subtropical Storm Alberto will reach Illinois on Wednesday, bringing widespread rain to areas that are driest in the state. By the time it reaches Illinois, it will have weakened considerably with the greatest risk from flooding instead of high winds. Here is the projected path:


And here are the projected rainfall totals for the next three days with possible totals of 2 to 4 inches in the southern third of Illinois and the risk for flash flooding in some areas, according to the NWS. Meanwhile, much of rest of the state could see amounts between 0.5 to 1.5 inches. The impact in western Illinois will be minimal.


This rainfall could be welcome in southeastern Illinois, which has been exceptionally dry in May. Here is the rainfall deficit map for May so far, showing some areas 2 to 4 inches below normal (1981-2010 average). If the forecast comes true, much of that deficit will be erased. Hopefully, the rains will fall slowly enough to soak in and help soil moisture. That has been the case in past situations such as Hurricane Isaac in 2012.


It is not that unusual for systems like this to reach Illinois and actually provide welcome relief from dry conditions. From a journal article that I wrote in 2006 about the impact of four tropical systems on the 2005 drought in Illinois,

The passage of four tropical systems alleviated drought impacts, particularly in southern and central Illinois during the 2005 growing season. The four systems were Tropical Storm Arlene, and Hurricanes Dennis, Katrina, and Rita. Several circumstances make this situation significant for Illinois. The historical tropical cyclone records indicate that while an occasional tropical system passes through Illinois, occuring in 26 years since 1851, 2005 was the first time for four such systems in one season. Timing of 4 to 6 weeks between tropical systems benefited agriculture while minimizing flooding. Tropical Storm Arlene and Hurricane Dennis also occurred relatively early in the growing season when critical moisture was needed. Aggregating the rainfall from these four events shows that they provided significant drought relief in southern and central Illinois during the 2005 growing season. Without those four systems, southern and central Illinois could have been in drought almost as severe as that in northern Illinois with 7- to 10-inch rainfall deficits instead of the observed 1- to 6-inch rainfall deficits.

From 099-14MS2611-print, Tropical Storms Reduced Drought in Illinois in 2005

For those sharp-eyed individuals, you may notice that Alberto is referred to as a subtropical storm, as opposed to a tropical storm. A good discussion of why it is a subtropical storm can be found at the Weather Channel. For us in Illinois, it really doesn’t make that much difference between the two types of storms (tropical vs subtropical) since they are no longer over warm waters by the time that reach us. In either case, they are much weaker upon arrival with the greatest risk from flooding rather than high winds.

Second Coldest April on Record in Illinois


Based on the official data, the statewide average temperature was  44.5 degrees,  8.1 degrees below normal. It was the second coldest April on record, only beaten by 43.1 degrees set in April 1907. Our statewide records go back to 1895. Normal refers to a specific benchmark, the 1981-2010 average. See the longer explanation here.

Here are the temperature departures from normal look like across the Midwest. Areas in green are 1 to 9 degrees below normal, while areas in icy blue are 9 or more degrees below normal. The lowest temperature reported in Illinois for April was -1 at both Avon and Lincoln on April 2. At the other extreme, we did reach into the 80s at times during the month. The warmest reading was 86 degrees at Kaskaskia on April 13.



The statewide average precipitation for April in Illinois was  2.37 inches,  1.41 inches below normal. In general, areas in the north and west had lower precipitation totals and were part of a larger area of below-normal precipitation that extended into Missouri, Iowa, Kansas, Nebraska, and beyond. Precipitation is the combination of both rainfall and the water content of snow.

The largest monthly total precipitation was Metropolis, home of Superman, with 6.73  inches as reported by the CoCoRaHS observer (IL-MC-2). On the other extreme, the Quincy Airport reported only 0.63 inches for the month and reflects the other low totals in the area.


Snowfall was widespread across Illinois in April, which is highly unusual. Parts of central Illinois received more snow than northwest Minnesota. Snowfall was above-normal across most of the Midwest. The largest reported monthly total in Illinois was 12.0 inches at Augusta, IL (Hancock County).




Cold Start to April in Illinois

The statewide average temperature for Illinois from April 1-11 was 35.6 degrees, 12 degrees below normal. While we are having a few days of warm weather now, we are expected to get right back into colder weather over the weekend. The NWS forecast for the next 14 days shows an overall picture of below-normal temperatures. Even so, I expect the departures from normal won’t be quite as severe as the first 10 days of April.

If you are thinking that you have never seen an April this cold, you are probably right. Here are the top ten coldest Aprils in Illinois. You have to go back to 1983 and 1982 for some really cold Aprils.

Rank Year Average Normal Departure
1 1907 43.1 52.6 -9.5
2 1926 45.2 52.6 -7.4
3 1904 45.6 52.6 -7.0
4 1950 45.8 52.6 -6.8
5 1920 45.9 52.6 -6.7
6 1961 46.6 52.6 -6.0
7 1918 46.7 52.6 -5.9
8 1983 46.8 52.6 -5.8
9 1982 47.0 52.6 -5.6
10 1928 47.4 52.6 -5.2

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Fourth Wettest February-March on Record for Illinois

Note: The web address of the State Climatologist website has changed to https://www.isws.illinois.edu/statecli/  Please update your links to reflect this. Some links are still being fixed. I apologize for the confusion – I just learned about this myself on Friday afternoon. 

February-March: The statewide average precipitation for the February-March period was 8.69 inches and the 4th wettest February-March on record. The wettest was 1898 at 8.96 inches. So we didn’t miss the record by too much. Here are the maps for the accumulated precipitation and departures from normal for February-March (click to enlarge). Precipitation is a measure of both the rainfall and the water content of any snow. These numbers are preliminary and subject to change.

March Precipitation: March ended up cooler and wetter than normal. The statewide average temperature was 38.7 degrees, 2.6 degrees below normal. The warmest reading for the month was 75 degrees at Kaskaskia River Navigation Dam on March 16. The coldest reading for the month was 10 degrees at Mt. Carroll on March 9.

March Temperature: The statewide average precipitation for March was 4.03 inches, 1.07 inches above normal. The largest monthly precipitation total was 8.38 inches at Carlyle, IL. Here are the maps of accumulated precipitation and departures from normal for the month of March.

March Snowfall: The snowfall pattern for March was largely the result of one storm on March 24-25 that extended from the Quad Cities to Danville. The largest monthly snowfall total for March was 11.4 inches at Eureka, IL. The rest of the state saw little snow in March.

So, what’s the outlook for April? According to the National Weather Service, more of the same – an increased chance of below normal temperatures and above normal precipitation for Illinois and the Midwest. Maps below.

April Fool’s Snow Storm

The April Fool’s Day/Easter Snow Storm of 2018 stretched across the central US. The bad news is that some areas saw 3 to 6 inches of snow or more. The good news is that the warm ground, warm air, and sunshine today quickly took care of it. The highest total I saw was Augusta, IL (Hancock County) with 9.0 inches.


In addition, we had cold temperatures over the snowpack. The lowest reading was -2 at Paxton.

Low temperatures on Monday, April 2

BTW, the average April snowfall in Illinois ranges from just over an inch in northern Illinois and is essentially near-zero in the southern half of the state. Therefore, April snowfall is not that unusual in northern Illinois but it is very unusual where it fell this time across central Illinois.