After some sizable rains in August and a nice contribution from TS Isaac over the Labor Day weekend, it should come as no surprise that the US Drought Monitor has revised the drought depiction for Illinois (see Figure). Besides the rainfall, we have seen major gains in soil moisture conditions and stream flow.
Large areas of Illinois were upgraded by one or two categories of the US Drought Monitor. Most notable is the reduction in two most severe drought categories: D3 and D4. The D4 category went from 7.8 percent to zero percent. The D3 category went from 69.6 to 6.96 percent – a ten-fold reduction. D4 was present in parts of 10 counties in northern Illinois. Much of the state still remains in D1 or D2 drought. We have an area in northeast Illinois categorized as just abnormally dry.
While the impact from TS Isaac has been remarkable, concerns remain for some lakes and rivers as well as shallow groundwater sources. The statewide average precipitation after Isaac is at 20.8 inches, still about 6.3 inches below normal.