Fall Color

One of the best things about this time of year is the fall color. I suppose I’m hopelessly Midwestern because I even enjoy the change in color of the corn fields.

The question I often get is “How will the weather affect this year’s color?” It is hard to answer. Here are some comments I made in a press release a few years ago about the recipe for good fall color.

“Trees and shrubs need to go into the fall without a lot of stress from disease or severe drought. Chilly, not frigid nights and cool, sunny days enhance the changing leaf colors. Detrimental conditions include extended periods of rain or cloudiness that mute colors, high winds that blow leaves off trees, and hard freezes that stop color changes entirely… October and early November in Illinois should put on quite a show. Take some time to go out and enjoy it,” concludes Angel.

Check out the official site of the Illinois Office of Tourism for fall activities. The University of Illinois Extension Service site called “The Miracle of Fall” is an excellent source of information as well. [Update] NOAA has a featured story on fall color that includes a link to a more technical discussion of fall leaf color.


Miracle of Fall
University of Illinois Extension site on "The Miracle of Fall".


Historical Record High Temperatures

With the recent warm weather, have you wondered what the record high temperatures are for Chicago and elsewhere? In the last few years, a group composed of NWS, Regional Climate Centers, and State Climatologists stitched together the weather records for 270 major metropolitan areas. The results of this project can be found at http://threadex.rcc-acis.org/

The sites in Illinois include Chicago, Moline, Peoria, Rockford, and Springfield. Amongst other things, the program reports the daily record high and low temperature and precipitation.

Here I selected the record highs for Chicago and pulled out the results for September. The program gives you the top three candidates and their dates.

Threaded Climate Extremes for Chicago Area, IL
Period of record: 1872 - 2009
Date	Highest Maximum Temperatures (degrees F)
Top 	Record		2nd Record	3rd Record
9/1	101 in 1953	96 in 1984	95 in 1960+
9/2	101 in 1953	98 in 1922	97 in 1913
9/3	97 in 1953	95 in 1960	95 in 1947
9/4	95 in 1983	95 in 1960	95 in 1954
9/5	98 in 1899	97 in 1954	95 in 1983+
9/6	97 in 1960	97 in 1954	96 in 1990+
9/7	100 in 1960	100 in 1939	99 in 1985
9/8	96 in 1960	96 in 1959	96 in 1933+
9/9	95 in 1983	95 in 1959	95 in 1955
9/10	95 in 1983	94 in 1964	94 in 1931+
9/11	95 in 1952	92 in 1908	92 in 1895
9/12	96 in 1952	94 in 1939	93 in 1962
9/13	98 in 1939	95 in 1927	94 in 2005+
9/14	99 in 1939	95 in 1927	95 in 1893
9/15	99 in 1939	94 in 1927	92 in 1955
9/16	92 in 1955	92 in 1931	89 in 1948+
9/17	93 in 1955	90 in 1988	90 in 1891
9/18	94 in 1955	92 in 1953	90 in 1963+
9/19	93 in 1955	92 in 1963	92 in 1948
9/20	91 in 1931	91 in 1895	90 in 1980+
9/21	92 in 1970	90 in 1931	90 in 1924+
9/22	92 in 1956	90 in 1986	90 in 1959+
9/23	91 in 1937	88 in 1892	87 in 1945+
9/24	91 in 1891	90 in 2007	90 in 1920
9/25	90 in 1933	89 in 1920	89 in 1900
9/26	90 in 1998	87 in 1973	86 in 1999+
9/27	91 in 1971	89 in 1987	89 in 1954
9/28	92 in 1953	90 in 1952	89 in 1971
9/29	99 in 1953	87 in 1921	87 in 1898
9/30	92 in 1971	88 in 1943	87 in 1952
+ indicates same value also occurred in a previous year.

Better Weather for Pumpkins in Illinois

I have to admit – I am a big fan of pumpkin pie. So I was concerned about the news stories about the pumpkin shortage. It turns out that Illinois is home to 95 percent of pumpkin production used for pie filling. In fact, Morton, in central Illinois, is considered the pumpkin capital of the world.

Last year was terrible for pumpkin production around Morton. After a wet growing season, October rains that were 3 times the average, over already wet fields, prevented growers from harvesting most of the 2009 crop.

Conditions in 2010 around Morton have been better so far. After a wet start, conditions in July and August were much drier. And the NWS forecast for October is for increased odds of warmer and drier than normal weather. Here’s to a successful pumpkin harvest.

Monthly Rainfall Totals (inches) for Morton, IL for this year, last year, and average (1998-2008).
Month 2010 2009 Average
April 3.8″ 7.3″ 3.8″
May 6.2″ 5.7″ 4.9″
June 6.8″ 5.1″ 4.0″
July 3.8″ 3.1″ 3.9″
August 2.0″ 4.5″ 3.2″
September 1.7″ 2.6″ 2.9″
October 8.9″ 2.9″

**the total for September, 2010, is through the 17th.

Outlook for Fall – Warm and Dry

NOAA’s Climate Prediction Center issued new outlooks today for October and beyond. The latest outlook for October shows all of Illinois having increased chances of being both warmer and drier than normal.

BTW, this is the exact opposite of how last October turned out. The statewide precipitation total in October 2009 was 8.40 inches. That was 5.5 inches above normal and the 2nd wettest October on record. The statewide average temperature was 49.6 degrees. That was 4.6 degrees below normal and the 6th coldest on record.

The outlook for October-December shows all of Illinois having an increased chance of warmer than normal conditions. Precipitation has “equal chances” of being above, below, and near-normal, or what I call a neutral forecast.

NOAA CPC forecast for this fall. Click to enlarge.

Tornado Tally for 2010 in Illinois

Based on data from the NOAA Storm Prediction Center, there have been 46 tornado reports in Illinois in 2010, as of September 14. These reports are based on damage at a particular site. The real number of tornadoes is often less than the first reports, as further analysis may show that the same tornado produced damage in two or more locations.

Most of the tornado activity for 2010 occurred in June with 39 reports (figure below). Many of those occurred in tornado outbreaks on June 5 (SPC report) and 21 (SPC report).

Of course, the 2010 tornado season is not over yet. The climatology of tornadoes in Illinois shows that it is possible to have tornado activity somewhere in the state all the way through December.

Illinois tornadoes 2010
Number of reported tornadoes in Illinois in 2010, as of September 14. Data courtesy of the NOAA Storm Prediction Center.

Tropical Storm Hermine Reaches Illinois

The remains of Tropical Storm Hermine have reached Illinois this morning. Rainfall amounts of 1 to 3 inches are possible and flash flood warnings have been issued. Check the National Weather Service as this event unfolds.

While we don’t often use the words “tropical” and “Illinois” in the same sentence, the remains of tropical storms and hurricanes have reached us before. Most of these systems came on shore in Texas and Louisiana and weakened considerably as they moved northward. Usually, the severe weather is gone by the time they reach Illinois but they can produce large amounts of rain than can lead to flooding.

The passage of four tropical systems alleviated drought impacts, particularly in southern and central Illinois during the 2005 growing season. The four systems were Tropical Storm Arlene, and Hurricanes Dennis, Katrina, and Rita. An article in the Illinois State Academy of Science by me described that situation in more detail.

More recently, in September 2008 the remains of Hurricanes Ike and Gustav produced heavy rains and flooding in Illinois. More on that particular situation can be found on my website.

Summer – One of the Warmest and Wettest on Record


This summer was one of the warmest and wettest in Illinois history, based on preliminary data. The average statewide temperature for this summer (June-August) was 76.4 degrees, 2.7 degrees above normal and the seventh warmest summer on record. The average statewide rainfall was 16.7 inches, 5.2 inches above normal and the sixth wettest summer on record. Statewide records for Illinois extend back to 1895.


The average statewide temperature for August was 76.8 degrees, 3.2 degrees above normal. That puts it at the 13th warmest August on record.  August was on track to being even warmer but a late-month cool spell knocked it down a few notches in the ranking. August rainfall has been close to normal with a statewide average of 3.4 inches, just 0.3 inches below normal.

[This is an update of a post earlier in August, now removed to avoid confusion]