WGN-TV Chief Meteorologist Tom Skilling and the WGN Weather Center staff provide daily coverage of weather in the Chicago area.

Dailey: September 2009 Archives

Rain, humidity arrive, and mild temperatures remain in Chicago

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It's been a long time coming, but rain moved into northeast Illinois, southern Wisconsin and northwest Indiana Sunday afternoon, ending a dry period that started in late August. Rainfall totals by Sunday evening ranged from a quarter to a half inch over the metro area. Earlier on Sunday, heavy rains downstate caused flooding of creeks, streams and susceptible roadways. There were numerous reports of one and two inch rainfall, and several locations in central Illinois received well over three inches. Jacksonville, just west of Springfield, recorded 4.76 inches. More flooding and 3-inch-plus rains occurred along the Ohio River in northern Kentucky and southern Indiana. All this rain was actually the northern edge of the record rainfalls that have been occurring across the Gulf Coast states as well as Missouri, Arkansas and Tennessee.

Cloudiness and showers to dominate forecast into next weekend
A strong low pressure system to the lee of Rockies over the Central Plains is forecast to remain essentially stationary much of the week ahead, finally ejecting to the northeast next weekend. This will mean an almost continuous flow of warm, moist air north up the Mississippi Valley, occasionally reaching northern Illinois and resulting in extensive cloudiness and periods of showers/thunderstorms, rather high humidity, and mild temperatures for the Chicago area.

Chicago's dry streak could come to an end Sunday

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It's been two weeks since September's only rainfall was recorded at O'Hare International Airport, Chicago's official observing site. It won't take much rain to exceed our entire monthly total of 0.03 inch. The high pressure regime that has produced an almost steady east wind along with the dry conditions and mild temperatures is finally breaking down. A low pressure system is set to establish itself over the Rockies and influence weather over the Midwest this week. A southerly flow up the Mississippi River Valley should feed warm, moisture-laden air into Illinois, resulting in considerable cloudiness. Even though showers or thunderstorms will probably not occur every day, it will be difficult for meteorologists to leave rain out of the daily forecasts.

Eastern U.S: A land of contrasts
The upper-air blocking pattern has persistently held the center of cold high pressure over the Northeast. Sunday morning frost and freeze advisories were posted for most New England states as well as northern lower Michigan. Meanwhile, persistent low pressure to the south has resulted in record heavy rains and flooding over the Gulf Coast the past week. Atlanta was among the latest, reporting a record daily rainfall of 3.7 inches Saturday.


Mild, hazy weather continues over northeast Illinois

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The upper-air pattern remains relatively unchanged with the stronger northern jet stream winds well to the north in Canada and the southern jet running from the Gulf of Mexico up the eastern seaboard. The light winds aloft leave little opportunity for any significant air mass changes here in the Midwest or western Great Lakes. As a result, the light easterly flow continues to allow fine particulate concentration to slowly increase, and hazy conditions will persist. In Wisconsin the Department of Natural Resources has continued an Air Quality Watch through Monday over southern and central portions of that state with concern that particle pollution and ozone concentrations might reach unhealthy levels for people in sensitive groups.

Rain/cooler conditions possible next weekend
Computer models indicate a cold front accompanied by showers and thunderstorms could bring cooler Canadian air into northern Illinois next weekend. Chicagoans may be in store for highs in the 60s, more like late September and early October.