September in Illinois: Cooler and Wetter Than Normal

September

The statewide average temperature for September in Illinois was 64.6 degrees, 1.6 cooler-than-normal. This was the first cooler-than-normal month of 2012, and the first cooler-than-normal month since September of 2011. See graph below.

The statewide average precipitation for September was 4.9 inches, 1.7 inches wetter-than-normal. This is the first wetter-than-normal month in 2012. See second graph below.

Much of the September rainfall came from the remains of Hurricane Isaac that passed over Illinois on Labor Day weekend. Additional rains fell later, especially in south-central Illinois. In general, areas south of Interstate 80 had monthly totals in the 3 to 12 inch range. A few sites in that region reported over a foot of rain with the largest total at Centralia with 15.89 inches. See first map below.

Precipitation totals north of Interstate 80 were around 1-2 inches. One of the driest spots in the state was Elburn (Kane County IL-KN-30) with only 1.28 inches for the month. Chicago and Rockford were not far behind with O’Hare Airport reporting 1.76 inches while the Rockford airport reported only 1.74 inches for September.

By the end of September, drought conditions had eased somewhat according to the US Drought Monitor.  Only 6.7 percent of the state was in the worst two categories  of drought (D3 and D4). This compares to 70 percent of the state in the two worst categories at the end of August. Even so, 82 percent of the state still remained in some stage of drought at the end of September.

January-September

Even with a wet September, the January-September statewide precipitation total of 22.38 inches was 8.34 inches below normal and the fifth driest on record. Here are the top five:

  1. 1988 with 19.49″
  2. 1901 with 19.84″
  3. 1936 with 21.76″
  4. 1940 with 22.17″
  5. 2012 with 22.38″

Remarkably, the precipitation over the last two months has erased the precipitation deficit since January 1 in much of Fayette, Washington, Clinton, Bond, and Montgomery counties. Sizable deficits remain across much of Illinois, especially western and northern Illinois as well as far southern Illinois. See second map below.

The January-September statewide average temperature of 59.6 degrees was 4.1 degrees above normal. It was the second warmest January-September on record and just slightly cooler than the record of 59.7 degrees set in 1921.

Notes: “normal” refers to the 1981-2010 averages. Statewide temperature and precipitation records began in 1895.

Statewide temperature departures from normal for September in Illinois. Click to enlarge.
Statewide precipitation departure from normal for September in Illinois. Click to enlarge.
30-day precipitation total through the morning of September 29 for Illinois. The 30-day map for September 30 failed to run. Click to enlarge.
Year to date precipitation departures from normal through September 29 for Illinois. Click to enlarge.

Sunny and Dry Start to October

The first 10 days of October have been warm, dry, and sunny in Illinois.  The statewide average temperature is 61.3 degrees, 3.8 degrees above average.

The statewide average precipitation is zero. Only a handful of sites in far western Illinois have reported anything. The highest total so far in the state was 0.44 inches from a CoCoRaHS site near Carthage, Illinois.

The driest October on record in Illinois was 1964 with only 0.20 inches for the entire month. Last year (2010) was the 19th driest October with only 1.35 inches. However, October 2009 was second wettest with 8.40 inches.

Here is a look at how October precipitation has behaved since 1895 in Illinois. The green dots are the individual years. The alternating brown and green shaded area show below and above average precipitation, respectively. The average is based on the period of record (1895-2010). You can see a lot of year to year variability in the numbers and no clear long-term trends.

October precipitation in Illinois from 1895 to 2010. Click to enlarge.

September in Illinois – Cool

Based on preliminary numbers, the statewide average temperature for September in Illinois was 63.2 degrees, 3 degrees below average. That makes it the 13th coolest September on record for Illinois. The coolest September was 1918 with 59.3 degrees. Statewide records go back to 1895.

Despite the overall cool readings for the month, Labor Day weekend was very hot. Highs in the upper 90s and low 100s were common during that time. One of the hottest was Quincy with 104 on September 1. In all, at least 65 stations in Illinois either tied or broke daily records for high temperatures in early September (text file with details).

On the other extreme, the coldest spot for the month was Paw Paw with 32 degrees on September 15. Twenty-two stations either set or broke daily records for low temperatures (see text file for details).

The statewide average precipitation for September was 3.53 inches, 0.34 inches above average. Rainfall was stubbornly sparse in the areas hardest hit by drought where only 1-2 inches were common. Amounts in far southern and northern Illinois were much wetter at 4-8 inches.

The highest rainfall total for the month was by a CoCoRaHS observer in Bush, Illinois, with 8.42 inches. In second place was a CoCoRaHS observer in Harrisburg, Illinois, with 8.04 inches. The reported driest spot in the state was a CoCoRaHS observer in Warsaw with only 0.69 inches of rain for the month. CoCoRaHS observers are volunteers that use standard equipment and training. Therefore, their results are comparable to other networks.

September rainfall
September 2011 rainfall for Illinois. Click to enlarge.

Fall Color in Illinois

I love all four seasons in Illinois but I especially like fall. In fact, you could say I’m a falloholic. What’s not to like – the air is cool and crisp and the cloud formations are spectacular. One of the best things about fall is the changing color in the trees, shrubs, and grass.

Henry Garnet’s Sweetspire in the author’s front yard.

A great website for all things related to fall color is the University of Illinois Extension site called “The Miracle of Fall“. Check it out for fall color, foliage updates, photos, festivals, etc. You can also find out about fall activities in Illinois at the Office of Tourism site “EnjoyIllinois.com“. A few other sites to explore are:

One of things I get asked every year at this time is, “what is the effect of weather on this year’s fall color?” It’s hard to answer because there is no formula for this. In general, you don’t want drought conditions because the leaves just turn brown and fall off. Instead, you want nights to be cool but not freezing to trigger the change in leaves. Also, you want mild day time temperatures (not too hot) and sunny weather to really make the colors pop.

I hope you take time to enjoy fall in Illinois. I know I will.

Record High Sunshine in October

The Illinois State Water Survey has this fascinating press release.

October Solar Radiation in Illinois: Record High in 2010, Record Low Last Year

11/9/10

Source: Bob Scott, 217-333-4966, rwscott1@illinois.edu

Did it seem to you that the weather in October was quite a bit sunnier than in Octobers of the past? Do you remember last October as being rather cloudy?

If these are your impressions, you are correct, according to Bob Scott, Director of the Water and Atmospheric Resources Monitoring Program at the Illinois State Water Survey, a division of the Institute of Natural Resource Sustainability. Scott operates an array of weather sites across the state called the Illinois Climate Network, and one of the sensors on the stations measures solar radiation.

Solar radiation totals for October 2010 were higher than in any past October since sites were installed in 1989, while the solar radiation totals for 2009 were the lowest.

“Our sensors measure what we call direct solar radiation,” Scott said. “This includes pure sunshine and reflected sunshine from clouds and blue sky.”

October typically is drier than the spring and summer months that precede it, and sunshine in October is in a seasonal decline with fewer daylight hours and the sun getting progressively lower in the sky.

“But this October was much drier than normal,” Scott said. “Consequently, there were many more days with bright sunshine and fewer days with clouds and rain, as opposed to last October which had many rain events.”

During the 20-year history of the weather station in Champaign prior to last year, sunshine in October has averaged about 379 mega joules per square meter.

If you ignore the units, Scott said, the range of solar radiation values in October in Champaign through 2008 varied from a low of 328 in 2004 to a high of 414 in 1992. The very wet October of 2009 had a total of 264 units of solar radiation, while the very dry October of 2010 reported 449.

“Both prior maximum and minimum values were slammed in the past two years,” Scott reported.

The current dry conditions have now continued into November with strong indications that it too will see above normal solar radiation.

As far as a cause for these events, “There is none,” said Scott. “Our data by themselves are far too short of a record to suggest a cause, and they are on opposite sides of the scale from each other. Without more information, these data must be categorized right now as simple natural variability.”

-30-

October Was Warm and Dry in Illinois

Precipitation

For Illinois, the statewide average rainfall for October was 1.4 inches, 1.5 inches below normal or 48 percent of normal. This ranks as the 20th driest October on record. The largest monthly rainfall total was reported at Belvidere with 3.94 inches. See map below for rainfall departures across the state.

While northern Illinois was close to normal on rainfall in October, parts of southern and eastern Illinois remained dry. The U.S. Drought Monitor lists those areas as “abnormally dry” and southeastern Illinois as”moderate drought”. At this time of year, the main impacts on agriculture would be on pasture conditions and winter wheat.

Soil Moisture

With the vegetation preparing for a long winter’s nap and lower temperatures, the demands on soil moisture are close to zero. So soil moisture should start to recover in the next few months even if precipitation remains below normal. The Illinois State Water Survey posts their latest soil moisture survey a few days after the end of the month here.

Temperature

The statewide average temperature for October was 56.2 degrees, 1.6 degrees above normal. The highest temperature for the month was reported at Fairfield with 93 degrees on October 10. The lowest temperature for the month was reported at Minonk with 22 degrees on October 29 and Sidell with 22 degrees on October 30.

Frost

During October, nearly all of Illinois has experienced temperatures down to 32 degrees and many areas have reached 28 degrees or less. See map below.

Figures

 

October rainfall Illinois
October rainfall departures from normal.
freeze Illinois
Occurrence of Frost (32F) and Freeze (28F) in Illinois at end of October 2010.

 

 

All data are preliminary.