The fast-moving, downpour-generating lines of gusty thunderstorms, which have swept the Chicago area with some regularity in recent weeks as part of the "ring of fire" pattern, appear to be over for the time being. That doesn't mean our weather is to be completely rain-free. Though coverage will be a fraction of that during some of the more potent recent thunderstorm outbreaks, a few widely-spaced and isolated showers or thunderstorms may bubble up Thursday afternoon. They are likely to affect less than 15 percent of the area.
Computer wind trajectory forecasts, which allow the tracking of Chicago's weather from its source, indicate the air moving into the city Thursday is coming in from the northwest and has North Dakota and Saskatchewan Canada origins. Humidities there Wednesday were far lower than here. Dew points across North Dakota Wednesday, ranged from the mid 50s to the low 60s---well below the humid 70s registered here.
But Chicago area soils are moist in many locations in the wake of recent downpours. This is likely to cut into the degree of drying likely to occur Thursday. Though humidities will be noticeably lower than on Wednesday, computer projections suggest there will still be 1.30 inches of evaporated water in a column of air (the tally Wednesday was 1.87 inches). The plants growing in these wet soils are able to tap this moisture and transpire (or pass it through evaporation) some of it back into the atmosphere. There, it can contribute to spotty shower formation in the warmer hours of the day.
Wednesday's 77-degree dew point marks Chicago's most humid air in 8 years
Chicago's peak dew point Wednesday---a reflection of the amount of moisture in the air---was 77-degrees. That's high and an indication there was plenty of moisture present. A check of area weather records indicates that's the highest dew point to occur here in the 8 years since a similar 77-degree reading on June 30, 2002.
Chicago area storms produce wind damage and local flooding---but deflect oppressive downstate heat
Wednesday opened with a fast-moving, bow-shaped band of thunderstorms---some towering to 49,000 feet---racing across the metro area. That bow-shaped configuration of those storms on radar was important. Lines of thunderstorm, when bow-shaped, are often high wind producers. That was certainly the case early Wednesday. Gusts out of the eastbound storm complex reached 67 mph at west suburban Elburn, 61 mph near Deerfield, 60 mph in Naperville, Carol Stream and Westmont, 56 mph at O'Hare, 54 mph at West Chicago and 50 mph near Channahon and Coal City to Chicago's south. Rainfall was so heavy in some of the storms that roads in Rensselaer IN were covered by 4 inches of water.