The statewide average precipitation for the first half of September was 3.77 inches, which is already above the monthly normal precipitation of 3.24 inches.
However, that precipitation was not distributed equally around the state. The figure below shows that large areas across eastern and southern Illinois received 3 to 6 inches of rain (shades of dark blue and green). Meanwhile, areas north of Interstate 80 and in western Illinois were much drier with amounts of less than 2 inches. Most of the heavy precipitation fell from the remnants of Hurricane Isaac that passed through Illinois on Labor Day weekend.
Reports from individual stations ranged from 8.08 inches for the CoCoRaHS station Bush (IL-WM-4) in southern Illinois to only 0.57 inches for the CoCoRaHS station Geneva (IL-KN-1) in northeast Illinois.
Drought Eases Slightly in Illinois
Drought eases slightly in Illinois thanks to the rainfall and cooler temperatures of the last few weeks. The US Drought Monitor for August 28 shows improvement in northeast Illinois, especially Cook County.
While not yet reflected in the Drought Monitor, August has been a better month than July with more rain and milder temperatures. I’ll post the end of the month stuff on Friday. In the meantime, here are the latest departures from normal for the month so far (second figure). Parts of western and central Illinois as well as much of Illinois north of Interstate 80 have been below normal, areas in east-central and southern Illinois received above-normal precipitation for the month.
Of course, the real game-changer is yet to come – Tropical Storm Isaac. More on that later.
Rain Across the Northern Half of Illinois
We had some decent rainfall amounts in much of the northern half of the state in the last 24 hours. In this image from the NWS Southern Region, green is good – meaning that between 1 and 2 inches fell in those areas. Areas in blue received 3/4 of an inch or less.
Here in Champaign, we had 2.07 inches at the official site while I had 2.15 inches at my house. This is the largest 24-hour rainfall we have had since April 26, 2011. Also, it brings our monthly total to 5.56 inches, which is 1.63 inches above normal for August.
The second figure shows the precipitation departures from normal for August so far. Areas in green and blue are above normal, areas in gray are near normal, and areas in yellow are still below normal. Parts of northern Illinois are below normal as well as a wedge extending from Quincy to Decatur.
However, if you are thinking the drought is fading, the last map shows the precipitation deficits since January 1, 2012. Large areas of Illinois are still 8 to 12 inches below normal (yellow) and a few areas in central and southern Illinois are 12 to 16 inches below normal (red). We have a long ways to go before this drought is over.
Recent Rains Help in Parts of Illinois
Both rainfall totals and temperatures in August look far more promising than July. Here is the breakdown by climate division in August for Illinois. I apologize for the formatting – you will have to scroll left and right to see the entire table. By the way, in Illinois the climate divisions and crop reporting districts cover the same areas (see map below). I have a set of tables like these that update daily at Current Conditions in Illinois.
Temperatures for August are running 0.3 to 2.3 degrees below normal. Precipitation is running 0.4 to 1.4 inches below normal in the climate divisions to the north and west. The remaining climate divisions are above normal.
Illinois
08/01/2012 to 08/20/2012
Climate <------Temperature-----> <---------Precipitation--------->
Division Actual Normal Dev Actual Normal Dev Percent
-----------------------------------------------------------------------------
Northwest 69.4 71.7 -2.3 1.97 2.98 -1.01 66
Northeast 70.0 71.7 -1.7 1.97 2.84 -0.87 69
West 72.0 74.1 -2.1 1.08 2.50 -1.42 43
Central 71.3 73.2 -1.9 2.04 2.51 -0.47 81
East 71.0 72.6 -1.6 3.06 2.59 0.47 118
West-southwest 73.3 74.8 -1.4 2.31 2.16 0.14 107
East-southeast 73.7 74.8 -1.1 3.38 2.20 1.19 154
Southwest 75.8 76.1 -0.3 2.56 2.21 0.35 116
Southeast 75.7 76.2 -0.5 3.19 2.05 1.14 156
State 72.3 73.8 -1.5 2.39 2.46 -0.07 97
Dev means Deviation From Normal, Percent means Percent of Normal
Here are the temperatures and precipitation since January 1, 2012. While the recent rains are welcome, significant long-term precipitation deficits remain across the state.
Illinois
01/01/2012 to 08/20/2012
Climate <------Temperature-----> <---------Precipitation--------->
Division Actual Normal Dev Actual Normal Dev Percent
-----------------------------------------------------------------------------
Northwest 54.7 50.1 4.6 16.05 24.09 -8.04 67
Northeast 54.7 50.1 4.7 17.32 24.06 -6.73 72
West 57.4 53.1 4.3 14.39 24.77 -10.38 58
Central 56.8 52.5 4.4 14.19 24.57 -10.38 58
East 56.6 52.1 4.5 17.41 24.92 -7.51 70
West-southwest 59.0 54.6 4.4 18.17 24.71 -6.54 74
East-southeast 59.4 54.9 4.4 18.30 26.88 -8.58 68
Southwest 61.2 56.8 4.5 19.18 27.68 -8.50 69
Southeast 61.7 57.0 4.6 19.24 29.28 -10.04 66
State 57.8 53.3 4.5 17.12 25.52 -8.40 67
