For Immediate Release
|April 13, 2001||Source:||Jim Angel
Fax: (217) 333-6540
See-sawing Temperatures Indicate Spring Has Sprung in Central Illinois
Does it seem like spring in central Illinois rushes in all at once so that you need a jacket one day and shorts and a t-shirt the next?
"This spring the gap between 60- and 80-degree temperatures was 8 days in Champaign and 5 days in Chicago compared to an average gap of 61 days in southern Illinois, 51 days in central Illinois, and 49 days in northern Illinois,"according to State Climatologist Jim Angel of the Illinois State Water Survey (http://www.sws.uiuc.edu/ on the Web), a division of the Illinois Department of Natural Resources.
Southern Illinois is far less likely than northern Illinois to make a sudden switch from mild to hot conditions in spring because the climatologies for these regions differ. While 60-degree temperatures typically arrive earlier in southern Illinois (February 15 compared to February 23 in central Illinois and March 6 in northern Illinois), it takes longer to reach the next threshold of 80 degrees (April 15 or 16 in southern and central Illinois and April 23 in northern Illinois).
Angel used the number of days between the first 60-degree day in spring and the first 80-degree day as a measure of the abrupt change from spring to summerlike weather in a north-south transect of seven climate stations (see map) for which data were available from 1901-2001. Long-term stations in less urban locations were chosen to minimize the effects of a changing environment such as an urban heat island.
Angel found that Anna in southern Illinois experienced only two springs since 1901 when the two temperatures occurred less than 3 weeks apart compared to 17 springs in Dixon and Ottawa in northern Illinois. Going from south to north, springs with 3-week gaps or less occurred twice at Anna, five times at Mt. Vernon, four times at Pana, 11 times at Lincoln and Pontiac, and 17 times at Ottawa and Dixon. However, the most rapid warmup among the stations studied was a 24-hour period in Dixon in 1931 when temperatures were 66°F on April 7 and 83°F on April 8.
The numbers mean that rapid springtime warming is much more likely in the northern half of the state than in the southern half. Angel grew up in southern Missouri, which has the same latitude as Carbondale, and recalls springs warming more gradually than those in Champaign in central Illinois. Why is the springtime warming more dramatic in the north? One factor could be that late season snowfall delays warming until the snow has melted. By that time, abundant warm air to the south is brought swiftly northward by passing storm systems, leading to the rapid warming.
"In any case, spring is definitely here now so take some time to enjoy it. If you're itching to get outside and do some planting, keep in mind that the last frost date is April 14-21 in central Illinois, April 7 in southern Illinois, and April 21-May 1 in northern Illinois," advises Angel.
Long-term climate stations used to study rapid warming in spring.