August Near-Normal But Summer Hot, Dry for Illinois


After months of exceptionally warm temperatures and drought, Illinois finally experienced temperatures and precipitation closer to normal in August.

The statewide average temperature for August was 73.5 degrees, just 0.1 degree below normal. That’s about as “normal” as you can get.

The statewide average precipitation for August was 3.4 inches, which is 95 percent of normal. In the map below, areas in yellow and orange had 3 to 5 inches, while the areas in red had more than 6 inches. Areas in northern and western Illinois in green received less than 2.5 inches. The largest rainfall total in the state was at Grayville in southeast Illinois with 10.69 inches. In second place was Hoopeston with 8.33 inches.


The statewide average temperature for the three summer months of June, July, and August was 76.1 degrees, 2.6 degrees above normal. It was the eighth warmest summer on record in Illinois. The warmest was 1936 at 78.6 degrees.

The statewide average precipitation for June-August was 6.64 inches, 5.21 inches below normal. It was the sixth driest summer on record in Illinois. The driest was 1988 with 6.17 inches.

Year to Date

The statewide average temperature for January-August was 59.0 degrees, 4.2 degrees above normal. It was the warmest January-August on record in Illinois. The second warmest was 1921 with 58.3 degrees.

The statewide average precipitation for January-August was 17.45 inches, 7.31 inches below normal. It was the fourth driest January-August on record in Illinois. The driest was 1936 with 14.95 inches, followed by 1988 with 17.12 inches, and 1934 with 17.41 inches.

August precipitation for the last 30 days through the morning of August 31. Source: NWS. Click to enlarge.

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.

US Drought Monitor status for Illinois. Click to enlarge.
August precipitation, departure from normal. Areas in green and blue are above-normal. Map courtesy of the Midwestern Regional Climate Center. Click to enlarge.

Could Isaac Help the Illinois Drought?

As of noon on Monday, August 27, the track of Hurricane Isaac could pass through Illinois on Saturday (first map). Of course, it won’t be a hurricane – just a tropical depression. Even so, large rainfall amounts are expected to fall in parts of Illinois and Missouri (second map).

Back in 2008, I wrote about the impact of Hurricanes Ike and Gustav as the remains of those two systems dumped an impressive amount of rainfall across Illinois.

Perhaps a better comparison is with the drought of 2005. Like this year, Illinois was faced with a severe drought. However, the remains of four tropical systems brought needed rainfall into the region, especially southern Illinois (third map). The four tropical systems were Tropical Storm Arlene in June, Hurricane Dennis in July, Hurricane Katrina in August, and Hurricane Rita in September. In fact, the total rainfall from these four systems ranged from almost 8 inches in southern Illinois to about an inch in northern Illinois (fourth map). You can read more about the impact of tropical storms in 2005 in this article and this report (starting page 47).

Five day track forecast from the NWS issued Monday at noon, CDT. Click to enlarge.
Five day potential precipitation map, ending Saturday morning, from the NWS. Click to enlarge.
Tropical storm tracks in 2005 for Arlene, Dennis, Katrina, and Rita. Source: Illinois State Climatologist. Click to enlarge.
Precipitation contribution from four tropical systems that passed through Illinois in the 2005 growing season – Arlene, Dennis, Katrina, and Rita. Source: Illinois State Climatologist. Click to enlarge.

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.

Rains of August 26-27, 2012. Source: NWS. Click to enlarge.
August 1-27, 2012, precipitation departure from normal. Source: NWS. Click to enlarge.
Precipitation deficits since January 1, 2012. Source: NWS. Click to enlarge.

Midwest Drought and Barge Traffic

In the last few days there have been a number of articles like this one in the Peoria Journal Star about the slowdown of barge traffic along the Mississippi River due to the Midwest drought.

As the article mentions, we faced a similar situation in 1988. Stan Changnon, Illinois State Water Survey, wrote about the costs and other issues related to this in an article in the Bulletin of the American Meteorological Society.

Basically, in 1988 the barge industry lost about $1 billion due to low flows on the Mississippi as well as the Missouri and Illinois Rivers. The winner turned out to be the railroad industry as shippers scrambled to find alternative transportation for grain and raw materials.

Here is the graph of water levels on the Mississippi River at Chester, IL (south of St. Louis) since 2011. As you may recall, record rains in spring of 2011 caused much flooding on the lower Mississippi River. In fact, they had to blow some levies to save Cairo, Illinois. After facing heights of up to 40 feet in May 2011, levels fell throughout the rest of 2011 before leveling out in the winter and spring 2012. Since May of this year they dropped again to a current gauge height of about 1 foot. All these heights are in reference to the bottom of the gauge, not the bottom of the river. There is still water in the river – just not much.

You can find more of these at the USGS streamflow web site.

River stages on the Mississippi River at Chester IL since January 2011. Note the high stage last year of 40 feet, compared to about 1 foot this month. Source: US Geological Survey.

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.

                        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.

                        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
Climate divisions (and crop reporting districts) in Illinois.

Latest Outlooks for September and the Fall

On Thursday, NOAA’s Climate Prediction Center released their outlooks for September and the 3-month period of September – November. For Illinois, they foresee an increased risk of above-normal temperatures and below-normal precipitation in September. Also, they foresee an increased risk of above-normal temperatures for September – November. They are taking a neutral stand on fall precipitation, saying that there are equal chances of above, below and near-normal precipitation.

The other news they have is that their drought outlook (second figure) shows expected improvement in the drought north of Interstate 74 in the upcoming months. Some improvement is expected in southern Illinois. However, they expect drought to persist in western Illinois through at least the end of November.

NOAA’s CPC outlook for September and September-November. Click to enlarge.
NOAA CPC drought outlook. Click to enlarge.