The National Climatic Data Center has a web page that generates the snowfall climatology and extremes for any U.S. state except Hawaii (sorry).
From there you can pick a state and look at state-wide numbers like who had the greatest 1-day snowfall (24 inches at Coatsburg IL on Feb. 28, 1900) or the great snow depth (39 inches at Antioch on Jan. 16, 1979). You can also pull up more detailed station by station analysis of snowfall including averages and dates of the earliest and latest snowfall, etc.
Besides the cold temperatures, one of the initial signs of winter is that first snowfall. Parts of Iowa, Wisconsin, and Indiana have already seen their first snow. In the figure below are the median dates of the first measurable snowfall (greater than or equal to a tenth of an inch) of the season in Illinois.
Think of the median date as the date by which we have seen snow in 50 percent of the cases during the period between 1971 and 2000.
In northern Illinois, the first snowfall occurs around Thanksgiving. In far southern Illinois, you have to wait until sometime in mid-December.
In about 10 percent of the cases, the first measurable snow can occur as early as November 5 in northern Illinois to November 20 in far southern Illinois.
This is Winter Preparedness Week (November 14-20, 2010). As I write this, a major winter storm is moving through Minnesota and Wisconsin, so it is never too early to start preparing for winter conditions in Illinois.
Winter Storm Preparedness Guide
The Illinois Emergency Management Agency has teamed up with the National Weather Service and the American Red Cross to develop a Winter Storm Preparedness Guide (pdf). It provides information on winter storms, forecast terminology, and how to plan at home, work, school, and while on travel.
Having survived 50 winters in Missouri and Illinois, here is my short list of things to consider:
be alert to the current weather and forecasts – my family and I spent one Christmas Eve in a hotel in Springfield IL because I underestimated the snowfall and overestimated the ability of other drivers to drive in the snow;
dress appropriately – invest in a good coat, warm gloves, boots, hat, and scarf, you will be better prepared (and happier) in cold and snowy conditions;
be flexible in your travel plans – go early, stay later, or don’t go at all to avoid severe winter weather;
be prepared to be stuck at home for a few days – keep up stocks of food, water, and any medications;
be careful with heaters and fireplaces – many home fires and carbon monoxide poisonings have been the result of improper operation of space heaters, fireplaces, or using inappropriate devices such as barbecue grills. Trust me on this one – my father-in-law was the fire chief so I heard all the stories.
As a historical footnote, the concept of a winter preparedness week started at the Illinois State Water Survey in response to the severe winters of the late 1970s and early 1980s. It was done in partnership with the Illinois Department of Energy and Natural Resources and the Illinois Emergency Management Agency. Winter preparedness week was expanded through the National Weather Service, beginning around 1990.