Thanks to Jerry Plucinski for sending us this shot of Monday night's thunderstorms that he captured while boating in Lake Michigan 10 miles off shore.
Photo by Jerry Plucinski
A heat wave is a period of abnormally and uncomfortably hot and usually humid weather. In 1900, climatologist A. T. Burrows defined it as a spell of three or more days on each of which the high temperature reaches or exceeds 90 degrees. By that commonly accepted standard, Chicago experiences an average of three heat waves per year, and this year's first heat wave is now in sight.
But first, Chicago's temperatures will have to recover from the sharp, 17-degree cool-down that took Monday's high of 88 degrees down to 71 on Tuesday.
A major weather pattern change is now under way because the primary west-to-east jet stream is shifting into Canada. A jet stream typically forms between hot and cold air masses and its northward shift signals an expansion of heat across the United States. For Chicago, 90s arrive Saturday and persist into next week.
Dear Tom,
Is there a long-range forecast for the summer here in Chicago?
Helen Baker
Dear Helen,
NOAA's Climate Prediction Center prepares 90-day temperature and precipitation outlooks for the nation. The Center's current outlook for July and August into September calls for above-normal temperatures for practically all of the country, including the Chicago area.
The outlook also indicates equal chance for above- or below-normal rainfall. Because expected weather patterns show no particular rainfall preferences, a reasonable interpretation is that rainfall will be near normal.
The outlook for Chicago -- hotter summer temperatures than normal and near-normal rainfall -- therefore indicates a major departure from the current pattern of cool temperatures and very wet conditions.
A long last, the atmosphere is handing Chicago a three-day period of pleasantly sunny, cool and dry weather in what has otherwise been a cloudy, chilly and record-wet year. Year-to-date precipitation stands at 24.17 inches, the most ever for that period in 143 years of Chicago weather history -- and in remarkable contrast to the withering drought that prevailed at this time one year ago. Year-to-date precipitation then was a meager 12.64 inches. The weather doesn't play "catch up," but sometimes it seems as if it does.
Thundershowers moved across the Chicago area Monday afternoon, producing brief but heavy downpours. Selected rainfall totals:
0.30" Clarendon Hills
0.24" Downers Grove
0.20" Hinsdale, Western Springs
0.15" Midway Airport (courtesy of Frank Wachowski)
0.02" O'Hare International Airport
Canadian air that arrived late Monday afternoon has established residence across the Midwest and, in fact, is forecast to push to the Gulf states by Thursday. Chicago area locations that flirted with, and even exceeded, 90 degrees on Monday will struggle to get out of the 60s Tuesday. In yet another weather reversal, heat and humidity return by the weekend -- and that will bring the next threat for rain.
Until then, three rain-free days (Tuesday, Wednesday, Thursday) are expected, and that will be Chicago's longest "dry spell" in four weeks (since a 6-day dry period May 11-16).
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