The preliminary statewide average March temperature was 45.9 degrees, 4.5 degrees above the 1991–2020 average and the 13th warmest on record going back to 1895. Preliminary statewide average total March precipitation was 4.10 inches, 1.16 inches above the 1991–2020 average and the 30th wettest on record going back to 1895.
Data are provisional and may change slightly over time
Warm Start to Spring
Our suffering in February was rewarded by persistent mild temperatures in March. Figure 1 shows 23 out of 31 March days were warmer than the 1991–2020 average in the village of Normal.
As the maps below show, March average temperatures ranged from the low 40s in northern Illinois to low 50s in southern Illinois, which was between 3 and 5 degrees above the 1981–2010 normal (Figure 2). Last month, 20 daily high maximum temperature records and 16 daily high minimum temperature records were broken statewide. Chicago’s O’Hare Airport recorded a minimum temperature of 57 degrees on March 10, which broke the previous daily high minimum temperature record by 11 degrees.
The persistent warmth last month accelerated growing degree day accumulation and prompted an earlier than normal spring greening, the result of which was earlier stone fruit blooms. Unfortunately, an early bloom increases the risk of significant freeze damage to vulnerable crops such as peaches and cherries. This pattern is consistent with longer trends in early spring growing degree day accumulation. Figure 3 shows base 50 growing degree day accumulation between January 1 and April 1 each year and the date of the last spring 28-degree freeze between 1949 and 2020 in Belleville.
Growing degree day accumulation in the first three months of the year in Belleville shows a strong increase over the past seven decades, with a trend of 15 additional growing degree days per decade. Concurrently, the date of the last spring freeze has not changed significantly over that same time period and overall exhibits quite a bit of year-to-year variability. The combination of increasing heat accumulation in the first three months of the year with no appreciable change in the last spring freeze results in an overall increased risk of freeze damage to tender perennials and fruit trees.
The preliminary statewide average March temperature was 45.9 degrees, 4.5 degrees above the 1991–2020 average and the 13th warmest on record going back to 1895. In fact, last month was the warmest March statewide since 2012; however, the statewide average temperature last month was still nearly 10 degrees below that in 2012, demonstrating how unusually warm March 2012 was.
Have and Have Nots of March Rain
The first third of last month was very dry across the state. As the maps in Figure 4 show, most of the state north of Interstate 64 received less than 0.05 inches of precipitation in the first 10 days of March. A pattern change around the middle of the month brought several rounds of storms and heavier rain to southern and central Illinois. One CoCoRaHS observer south of Carbondale in Jackson County observed 3.98 inches of rain on March 12. In all, March total precipitation ranged from just over 1 inch in northeast Illinois to over 5 inches throughout most of southern Illinois. March precipitation departures ranged from nearly 3 inches above the 1981–2010 normal in southwest Illinois to nearly 2 inches below the 1981–2010 normal in northeast Illinois.
The heavier precipitation was received either well or poorly depending on the part of the state. Southern Illinois soils were previously at or above normal moisture levels coming into March, so the additional precipitation resulted in standing water in fields and minor to moderate flooding along the Big Muddy River and Wabash River, among others in the region. However, the rain was welcome on drier central Illinois soils. In response to the improvement in moisture conditions in central Illinois, the U.S. Drought Monitor removed all moderate drought in its March 16 map; the first time Illinois was free of drought since August 2020.
March isn’t usually an exceptionally snowy month, but most of the state will typically see some flakes in the first month of spring. Snowfall last month was well below normal statewide, attributable to the mild temperatures. Total March snowfall ranged from less than a quarter of an inch in north-central Illinois to just over 4 inches in northwest Illinois. March snowfall departures ranged from less than an inch below normal in far southern Illinois to nearly 5 inches below normal in northeast Illinois.
Overall, the preliminary statewide average total March precipitation was 4.10 inches, 1.16 inches above the 1991–2020 average and the 30th wettest on record going back to 1895.
Once past these first, cooler days in April, the Climate Prediction Center outlooks suggest warmer conditions are ahead. The 6–10-day outlook for the second week of April shows strongly elevated odds (70% to 80%) of warmer than normal conditions, with only slightly elevated odds of wetter than normal conditions. The warm, dry pattern to start the month will certainly help further progress spring greening.
Looking at the month of April as a whole, the 1-month Climate Prediction Center outlooks also show elevated odds of warmer than normal conditions, with an equal chance of above and below normal precipitation in April.