A deepening center of low pressure will move northeast out of Iowa through Wisconsin during the next 12 hours. The associated cold front will swing through Chicago from the west later Wednesday morning. Strong low-level (60 mph out of the south at 2000 ft) pulling increasingly more moisture-laden air into Illinois, southeastern Wisconsin and northwestern Indiana are linked to increasingly strong winds aloft topped by an expanding area of upper-level southwesterly 140 mph winds at the 38,000 ft level. Temperatures east of the cold front (eastern Iowa and Illinois) are in the middle 50s tonight, while west of the cold front over western Iowa readings are in the lower to middle 30s.
All these ingredients point to a period of moderate to heavy rains here after 3AM until say 10AM Wednesday. About the same time the developing instability is expected to bring a good portion of those strong low-level winds down to the surface – resulting in southerly winds possibly gusting to 40 miles per hour or more Wednesday forenoon.
The cold front should be moving through or east of Chicago by midday Wednesday with winds shifting to the northwest and rain tapering off. Temperatures will fall from the middle 50s through the 40s during the afternoon with readings in the upper 30s to lower 40s by evening.
As of 6PM winds had shifted to the west at all Chicago reporting stations – the shift from the south occurred between 4 and 6PM as a cold front swept east through the area. Cooler air will follow along with slowly diminishing showers. By midnight most of the showers should be east of our area and temperatures falling back into the middle 40s as gusty northwest winds pull cooler air into the Midwest and western Great Lakes.
A deepening center of low pressure will move northeast of lakes Superior and Huron, but the tightening pressure gradient around the low will keep winds up (gusts in excess of 30 miles per hour) through the night into the morning hours Friday.
Rainfall totals so far have ranged from under a half inch in some northern locations to over 4 inches. Heaviest rains were reported over central and southern portions of the Chicago area.
A sampling of storm total reports – all stations have had more rain since reporting:
Location Rainfall (inches)
Naperville 4.90 (see picture below)
Midway Airport 3.31
Willow Springs 3.44
Downers Grove 3.50
Chicago (SE) 3.20
Chesterton (IN) 3.00
The National Storm Prediction Center has placed a portion of the Chicago area – mainly just south and east of the city of Chicago – in a slight risk of severe thunderstorm area this afternoon.
With a 60 mile-per-hour warm moist southwesterly low-level flow over this area and east combined with a strong 130 mile-per-hour jet stream high overhead and a cold front approaching from the west, the Chicago area and especially points farther east appears in prime position for strong – possibly severe thunderstorm development this afternoon. Severe storms could continue farther east this evening.
Yellow-shaded area on map below depicts slight risk of severe thunderstorm area…
Urban and Small Stream Flood Advisory in effect until 9:30AM CDT for
Central Cook, northwestern Will, southern Kane and all of DuPage and Kendall Counties in northeast Illinois
At 3:30 this morning National Weather Service radar indicated heavy rainfall continues to fall over the advisory area with one to two-inches or more falling since midnight. Additional rains of an inch or more are possible yet this morning.
Runoff from this significant rainfall will cause flooding to occur along small streams and near low water crossings such as viaducts and underpasses.
Some cities/towns that may experience flooding are:
Addison..Alsip..Aurora..Batavia..Geneva,..St. Charles..Berwyn..Blue Island..Bolingbrook..Brookfield..Burr Ridge..Carol Stream..Chatham..Chicago..Cicero..Downers Grove. Other locations that may be affected include..Argonne National Laboratory..Aurora University..Benedictine University..Brookfield Zoo..College of DuPage..the DuPage Airport..and the DuPage County Fairgrounds.
An Urban and Small Stream Flood Advisory is in effect until 3AM CDT Thursday for Southeastern Cook..Will and Kankakee Counties in Illinois and Lake..northern Newton..northern Jasper and Porter Counties in Indiana
At 11PM CDT heavy rainfall continues to fall over the Flood Advisory area. Rainfall of 2 to 2 and a half inches has already been reported at many locations and additional rains well in excess of an inch is likely well past midnight.
Runoff from this excessive rainfall will cause flooding of small creeks and streams..highways..viaducts and underpasses…some potentially affected areas are – Blue Island, Boone Grove, Bourbonnais, Bradley, Burnham, Burns Harbor, Calumet City, Cedar Lake, Chatham, Chesterton, Chicago Heights, Crown Point and De Motte.
Heavy rainfall between 1 and two and a half inches has been reported at several locations just south of Chicago during the evening. Lesser amounts between a quarter and three-quarters of an inch fell at scattered locations west and north of the city as well as in Chicago proper.
More rain is on the way overnight as a warm front pushes north through the Chicago area. Thursday a cold front will approach from the west with gusty southwest winds pulling warm moist unstable air into Illinois, southern Wisconsin, Indiana and Lower Michigan – triggering more showers and thunderstorms until the front passes east through the Chicago area Thursday evening.
Some rainfall reports as of 9:30PM…
Location Rainfall (inches)
Park Forest 1.69
By mid-afternoon the warm front associated with a low pressure center developing in western Iowa and eastern Kansas runs east across northern Missouri, central Illinois and Indiana into southern Ohio. An extensive blanket of lowering clouds extends over Iowa, Missouri, Illinois, Wisconsin, Indiana and Lower Michigan.
Rain will spread from west to east across the Chicago area impacting the late-day/early evening commute, and continuing overnight with a few claps of thunder possible. As the low pressure center intensifies and moves northeast, the warm front will pass through the Chicago area this evening – moving into Wisconsin allowing mild temperatures and high dew-point (60-degree) air to flow into northeast Illinois, southeast Wisconsin and northwest Indiana. Commuters should be aware that patches of dense fog could form along and ahead of the frontal boundary combining with the wet slick roads to cause hazardous driving conditions.
The cold front associated with this low pressure system will probably cross the Mississippi River headed east Thursday morning – eventually passing through the Chicago area later Thursday afternoon. Showers and a few thunderstorm downpours could bring storm total rainfall of one to more than two-inches before the cold front moves to our east and rain ends later Thursday.
Overcast skies and patches of widespread haze, fog and light drizzle blanket much of northern Illinois and southern Wisconsin into the portions of northwest Indiana this morning. A Dense Fog Advisory for visibilities below a quarter mile is in effect until 11AM this morning away from the city of Chicago where warmer temperatures have tempered the lowering of visibilities.
A warm front attached to developing low pressure in Kansas and Nebraska extends from the low through northern Missouri and southern Illinois along and just north of the Ohio River farther east. A wide expanse of lowering cloudiness and haze/fog has developed north of the warm front over Iowa, Illinois Wisconsin and Indiana. As the center of low pressure deepens and slowly moves northeast, the warm from will nudge north – approaching Chicago later today and this evening, probably passing through our area tonight.
While some improvement in visibility is expected later this morning into the afternoon, low clouds and hazy conditions are expected to persist with conditions deteriorating later this afternoon and evening as the warm front approaches the Chicago area. Showers could also develop along and ahead of the front. Much milder temperatures and higher dew-points (in the upper 50s and lower 60s) will surge into northeast Illinois tonight setting the stage for stronger shower and thunderstorms as a cold front approaches from the west Thursday.
Some fog/visibility reports as of 9:30AM this morning…
Location Lowest visibility (miles) Current Vis (9AM)
DeKalb .15 .15
West Chicago 1.25 1.75
Joliet .15 1.00
Rochelle .25 .25
Morris .25 .25
Pontiac .25 .25
Ottawa/Peru 1.00 1.25
Kankakee 1.25 1.75
Rockford .25 .50
O’Hare 3.00 4.00
Midway 1.25 2.50
Palwaukee 2.50 3.00
Waukegan 4.00 4.00
Kenosha, WI .15 1.00
Janesville,WI .25 .25
Gary, IN .50 4.00
Valparaiso,IN 2.00 2.00
Lansing .25 3.00
Peru in La Salle County 1.0″
Lisbon in Kendall County 0.1″
Snow was falling earlier this afternoon across portions of the Chicago area
especially in areas west and south of the city. Up to 2 inches of snow
covers grassy areas in portions of La Salle County.
At 3pm most reporting station were reporting light rain, though light
snow was still being reported at the Aurora airport in Sugar Grove.
CHICAGO AREA WEATHER ROUNDUP
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
300 PM CDT TUE OCT 22 2013
NOTE: "FAIR" INDICATES FEW OR NO CLOUDS BELOW 12,000 FEET WITH NO
SIGNIFICANT WEATHER AND/OR OBSTRUCTIONS TO VISIBILITY.
* THESE STATIONS ARE NOT UNDER NWS QUALITY CONTROL. THEY ALSO MAY NOT
REPORT WEATHER SUCH AS PRECIPITATION OR FOG.
CITY SKY/WX TMP DP RH WIND PRES REMARKS
OHARE LGT RAIN 38 35 89 SW9 29.92F
MIDWAY LGT RAIN 38 35 89 SW7 29.94F
AURORA LGT SNOW 36 33 89 CALM 29.93F FOG
LANSING* RAIN 37 33 87 CALM 29.94F
JOLIET* LGT RAIN 34 32 94 CALM 29.94F
WAUKEGAN CLOUDY 43 26 51 VRB5 29.90F
DUPAGE AIRPORT LGT RAIN 37 34 89 CALM 29.92F
WHEELING CLOUDY 42 31 64 SW7 29.93F
MORRIS* RAIN 36 34 92 NE3 29.91F
LEWIS AIRPORT* RAIN 35 34 94 CALM 29.93F
NORTHERLY IS N/A 39 36 89 SW9 N/A