“Statewide, June temperatures averaged 70 degrees, 1.9 degrees below normal— the 30th
coldest June since 1895—and now July is following this same pattern, with temperatures for the
first nine days of July averaging 2.4 degrees below normal,” says State Climatologist Jim Angel
of the Illinois State Water Survey (http://www.sws.uiuc.edu), a division of the Illinois
Department of Natural Resources.
Since April 1, there have been 1462 growing degree-days statewide compared to 1440
such days normally during this period. Growing degree-days, based on the number of days with
temperatures above a 50-degree threshold, are used to estimate the rate of growth rate of crops.
Temperature extremes last month ranged from 96 degrees at Hutsonville on June 12 to 40
degrees at Mount Carroll on June 26. That’s quite a jump but no surprise. The first 18 days of
June were 2.2 degrees above normal, while the last 12 days were 8 degrees below normal. The
last 12 days were the second coldest end of June since 1900, beat only by June 19–30, 1902,
which was 10.3 degrees below normal.
June rainfall throughout Illinois was 87 percent of normal, 3.57 inches. Joliet reported
the heaviest one-day total, 4.02 inches on June 12. Hoopeston reported the heaviest monthly
total, 9.23 inches. So far July has been wetter than normal, 1.78 inches compared to 1.09 inches
normally. As a result, soil moisture in the top 6 inches is 75–150 percent of normal in most of the
state. Southeastern Illinois is the only dry area, with the soil moisture site at Olney reporting just
under 50 percent of normal in this top soil layer as of July 6, the last day surveyed.
The National Weather Service calls for above normal temperatures and precipitation next
week, followed by cooler, drier conditions. “This means that July precipitation could end up
being at or above normal with temperatures at or below normal,” says Angel.
“Historically, there is a weak positive correlation between July and August temperatures
(for example, a cool August is somewhat more likely to follow a cool July) but almost no
correlation between July and August rainfall. In fact, last year August was very dry after a wet
July,” concludes Angel.
