A sunny and warm Sunday afternoon turned showery late as rains developed along a wind-shift line moving southeast out of Wisconsin. Though the showers were low-topped and produced little thunder and lightning, they did spawn numerous funnel clouds west of the city along a corridor between Interstate Highway 39 and the Fox Valley. These funnels were "cold air-type funnels," the kind not associated with severe thunderstorms that almost always dissipate without producing any damage.
After a chilly 4th of July, temperatures rebounded into the comfortably warm lower 80s Sunday, a level expected to repeat here through midweek. Hot weather has been noticeably absent from the city since a streak of 90s in late June, but the latest suite of computer forecasts hints at a brief surge of hot weather that should reach the city by Friday. The downside to the expected warm-up will be a threat of showers and thunderstorms that will continue to add to the city's growing 2009 precipitation total that has now reached 26 inches -- nearly three-quarters of the city's normal annual total of 36.27 inches.
Dear Tom,
On average, how many days a year does Chicago experience fog?
Alice H.
Dear Alice,
On many cool, calm mornings around sunrise, parts of the Chicago area, especially in the suburbs, will experience ground fog as the air cools to saturation. The fog usually burns off quickly, creating only brief inconvenience. There are many other days where light fog is present from a variety of causes resulting in reduced visibility. However, there are only an average of about 12 days each year when Chicago is socked in with dense fog (visibility one-quarter mile or less) that seriously impacts transportation. Dense fog is most common here during the cold season, frequently occurring when warm, moist air passes over cold snow-covered ground. December through March hosts a majority of the area's dense fog occurrences with each month averaging about two days.
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