Chicon 2000

Weather

Rev. 26-Mar-2000
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Background

Weather in Chicago, as in most cities, is highly variable. Fortunately, it's also very predictable.

There are two geographical factors that contribute to Chicago's weather. First, there is Lake Michigan, one of the Great Lakes. 450 miles long, 80 miles wide, 900 feet deep. The second is that there really isn't any major geographical features to the west or south of Chicago for nearly a thousand miles (1600 kilometers).

The effect of the latter is simple. Once weather events start heading to Chicago, there is nothing in the geography to stop them. This means that there is usually two to three days warning before any major weather systems hit Chicago. This also means that any weather system that happens to head to Chicago tends to get there. This makes Chicago weather very variable in the long term -- you never know what may get thrown at Chicago. But it also tends to be predictable in the short term. If a weatherman in Chicago says expect rain, believe it, since the system bringing rain has probably been marching to Chicago for the last week.

The Lake is a little more complicated. As any huge mass of water does, it makes a dandy thermal mass. It tends to be much warmer that the air over it in winter, and much cooler than the air in summer. In winter, this bring lake effect snows that can drop six inches of snow on downtown while leaving the suburbs dry. In summer, this brings the lake breeze, which can drop the temperature dramatically downtown.

The Chicon 2000 hotels are located downtown, right on the Chicago River, and less than half a mile (less than one kilometer) from the Lake. This means that the Chicon hotels catch both the lake effects, and the wind effects that often occur as wind blows along the river and between the skyscrapers of downtown.

Historical

Last year, during the last two weeks of August, and the first two weeks of September, the highest temperature recorded was 92 degrees, and the lowest was 42. August and September are typically some of the drier months for Chicago, with most of the rainfall occuring during short thunderstorms. Average winds were about 8 mph. Downtown, near the Lake, there is usually an on-shore wind blowing, since the lake rarely reaches 70 degrees. This results in temperatures downtown dropping 5-10 degrees below the offical temperatures measured at O'Hare, and as much as 20 degrees cooler right on the Lake itself.

What to expect, and what to bring

There are, of course, no certainties. But if you were to bet on one thing, expect at least one, if not most, of your days in downtown Chicago to be breezy. A windbreaker, even a thin shell one, can be the difference between comfort and chills. Westerly and Southerly winds tend to warm the city up, Northerly winds will cool it down, and Easterly winds double the lake effect cooling and tend to whip up quite a wind along the river.

You should pack for a late summer, since it does get warm, but throw in a sweater and a windbreaker. Umbrellas tend to be a real problem in Chicago, with the winds that often swirl around the skyscrapers, so most natives rely on raincoats instead. Fortunatly, the weather is usally quite mild during late August and early September, so Chicon 2000 member should be spared most of the extremes that Chicago is infamous for.

More information and forecasts.

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