Soils across Illinois were cooler and drier than average in the first half of August, said Jennie Atkins, the water and atmospheric resources monitoring program manager at the Illinois State Water Survey, part of the Prairie Research Institute at Illinois.
Soil temperatures at depths of 4 inches under sod averaged 75.8 degrees in Illinois during the first half of August, 1.2 degrees below the long-term average and 4 degrees lower than the same period in 2016. Daily highs reached the mid-90s with lows in the 60s. This follows the trends seen with air temperatures that are 3.6 degrees below normal as of Aug. 15.
Temperatures were also lower under bare soil, averaging 77.9 degrees at 2 inches and 77.4 degrees at 4 inches.
August has also been dry. Precipitation for the month was 1 inch below the long-term average as of Aug. 15. The drier weather has led to lower soil moisture levels throughout the state, with the largest decreases seen in northern and east-central Illinois. Soil moisture levels declined 11 percent at depths of 2 inches to a state average of 0.18 water fraction by volume on Aug. 15.
There were similar declines at depths from 4 to 20 inches. Soil moisture levels remained steady at 39 and 59 inches, averaging 0.41 and 0.40 wfv, respectively, on Aug. 15.