New Climate Normals for Illinois

The new 1981-2010 climate normals are available for Illinois. You can find them through a station list or a Google Map on my homepage.
Climate normals are 30-year averages that are updated every 10 years in the U.S. The National Climatic Data Center produces the climate normals for the US. By settling on a standard averaging period, users are able to compare climate conditions between two or more locations.
By updating every 10 years, the climate normals can reflect data from newer stations as well as reflect any changes to the climate.  One impact of switching from the 1971-2000 to the 1981-2010 climate normals was that the cold, snowy winters of the 1970s fell out of the calculations. As a result, the new normal snowfall has dropped a little in most places. For example, the new normal annual snowfall is 3 inches less in Champaign-Urbana.
The National Climate Data Center has a climate normals page dedicated to the new climate normals and frequently asked questions.

Snowfall Totals from around Illinois

The winter storm of February 1-2, 2011, will be remembered by many in northern and central Illinois. The National Weather Service (NWS) did an excellent job of producing forecasts and warnings on this storm. In the aftermath, we have began collecting the snowfall measurements from a variety of networks. Rather than list all the data here, I have provided some links to data sources.
Snowfall totals and some maps provided by NWS offices are available here:

Here is a preliminary look at snowfall totals across the Midwest. Snowfall amounts in excess of 12 inches extend from Oklahoma, into Missouri, the northern half of Illinois, and on into northern Indiana and southern Michigan.

Experimental Hour Snowfall Analysis
Preliminary snowfall totals map for the February 1-2, 2011 storm (NWS image).

And zooming in on northern Illinois.
Snowfall totals for the February 1-2, 2011, event in northern IL (NWS image).

Short-Term Weather Lore Holds a Kernel of Truth

Before the Internet, The Weather Channel, and NOAA radios, our ancestors relied on nature to tell its tale of upcoming weather. Moss growing on the south side of trees and squirrels hiding their nuts deep underground were thought to foretell a severe winter ahead.
Some natural prognostications like these are grounded in truth, given our current knowledge of meteorology, but others are purely fiction, according to State Climatologist Jim Angel of the Illinois State Water Survey at the University of Illinois at Urbana-Champaign.
Short-term weather forecasts based on nature observations are more likely to be accurate than long-term seasonal predictions.  In fact, there may be some merit to the notion that bad weather is coming when cattle lie down in the pasture and birds fly low.
“Many animals have a better sense of hearing and smell than we do, so when humidity, air pressure and wind direction change right before a storm, as well as the distant rumble of thunder, some animals may become restless,” Angel said.  “They can pick up on weather changes hours before we can.”
Predictions based on the appearance of the sky are thought to be particularly valuable, since certain clouds are associated with certain weather conditions, according to Angel.  Clouds described as mare’s tails and mackerel scales are very high-level cirrus and cirrocumulus clouds that can precede an approaching warm front, with rain not far behind.
Likewise, a halo around the moon is actually the refraction of moonlight through the ice crystals that make up high-level cirrus clouds, indicating an approaching low-pressure system bringing rain or snow.
Long-term forecasts, such as winter weather predictions, are much more uncertain.
“Centuries ago, it was important to determine how severe the winter would be so that adequate wood and supplies would be stored for the duration,” Angel said.  “The early settlers’ lives may have depended on their predictions, so they were grasping at anything to forecast the coming weather.  However, the size of the brown band on woolly worms, the groundhog seeing its shadow, or spoon-shaped persimmon seeds are just happenstance.”
Even with today’s modern technology, the theoretical limit of daily weather forecasts is about two weeks. Within the 6- to 14-day range, forecast errors can be large enough to limit their usefulness.
That is why forecasters typically only discuss general patterns of weather behavior beyond five days, usually in terms of probability or odds. For example, the 8- to 14-day forecast may show the eastern U.S. with an increased chance of below-normal temperatures.
The same is true for seasonal forecasts that are driven by both long-term trends and specific weather patterns such as El Niño.
For the upcoming winter, forecasters look at historical records to decipher a pattern.  The Midwest is under the La Niña effect, which is characterized by unusually cold waters in the eastern tropical Pacific Ocean.
The National Weather Service’s winter forecast for Illinois is an increased chance for above normal temperatures in the southern two-thirds of Illinois, and equal chances of above, below, and normal temperatures in the northern third of Illinois. All of Illinois has an increased chance of above normal precipitation.
What does the woolly worm predict?
Source: Jim Angel, Ph.D. (217) 333-0729, Fax: (217) 244-0220,
Editor: Lisa Sheppard (217) 244-7270,
The Illinois State Water Survey at the University of Illinois at Urbana-Champaign, a division of the Institute of Natural Resource Sustainability, is the primary agency in Illinois concerned with water and atmospheric resources.

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
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.