More rain fell over Illinois over the Memorial Day weekend. The heaviest amounts were in the central part of the state and ranged from 2 to 6 inches (yellow to dark red in the map below).
Right now the statewide average rainfall for May stands at 5.03 inches, based on preliminary data. More rain is forecasted for today and much of this week. So this total is likely to increase as we go through the week. By contrast, Illinois received only 2.5 inches in May 2012.
I have collected several discussions from NWS offices and elsewhere about the warm March and why it happened. Most of these reports offer more details about specific locations. The technical report goes into considerable detail about the underlying meteorological conditions.
In a nutshell (I always think of the Austin Power’s movie when I say that), March 2012 was dominated by unusually strong and steady flow of warm, moist air out of the Gulf of Mexico. That is in sharp contrast to a typical March where we swing back and forth between winter and spring-like temperatures as cold fronts and warm fronts often move through the state.
In fact, from a national perspective the widespread warm March has drawn comparisons to March 1910. See for yourself how these two compared.
The statewide average temperature for March in Illinois was 54.9 degrees, 13.8 degrees above normal. That makes it the warmest March on record. So here are the ten warmest March’s in the Illinois statewide records that date back to 1895:
The warmest temperature report in the state was Chicago O’Hare on March 21 with 87 degrees. The coldest temperature report was Monmouth on March 5 with 5 degrees.
The statewide average temperature for January-March in Illinois was 40.9 degrees, 9.1 degrees above normal. That makes it the warmest January-March on record. Here you will notice that the 2000s are on the list three times as are the 1990s.
The statewide average precipitation was 2.11 inches, 1.1 inches below normal or 66 percent of normal. The statistics are nothing like the March temperatures, but it did end up being the 31st driest March on record for Illinois. Precipitation was below normal across much of the state. However, there were a few wet spots with Fairview Heights (IL-SC-16) reporting the highest monthly total of 4.88 inches of precipitation. Here are the maps of accumulated precipitation and the departure from normal for March in Illinois.
With all the attention on the record warmth, it’s hard to remember that we did see snow in March. The largest monthly total was reported at Roscoe (IL-WN-2) with 5.6 inches of snow.
Based on data through March 29, the statewide average temperature was 54.7 degrees, 14.1 degrees above normal. Of course, we still have March 30-31 to go but all indications are that the much above normal temperatures will continue. So here are the ten warmest March’s in the Illinois statewide records that date back to 1895:
2012: 54.7°F (as of March 29)
Here are the ten warmest January-March’s in the Illinois statewide records. In this case, 2012’s hold on first place is more tenuous. Here you will notice that the 2000s are on the list three times as are the 1990s.
The statewide average rainfall of 5.6 inches in May, combined with the 2.8 inches in March and 7.3 inches in April, resulted in a total rainfall for this spring at 15.7 inches. That makes it the seventh wettest spring on record since 1895 and 4.3 inches above average.
The heaviest spring rains fell in southern Illinois. Cairo reported the highest total rainfall with 30.90 inches, followed by Brookport Dam with 29.19 inches, Du Quoin with 28.95 inches, and Carbondale with 27.59 inches. These numbers are slightly more than double the average spring rainfall totals.
[update June 7] I just found a CoCoRaHS observer near Anna (IL-UN-3) who reported 37.5 inches of rain during those three months. To put that in perspective, the average ANNUAL precipitation for the Anna area is 48 inches.
The statewide average temperature for this spring was 52.0 degrees, which is right on the 1971-2000 average of 52.0 degrees.
Note about “spring”: in climatology, we define spring as March – May. This definition lines up better with our ideas of spring weather than the astronomical definition of March 20 (equinox) to June 21 (solstice). In much of Illinois, spring weather starts to arrive before March 20 and summer weather starts to arrive before June 21.