Pre-storm “warming” has occurred Wednesday. O’Hare’s 66-deg high made this the warmest day of the past 6—but follows a 42-deg nighttime low at O’Hare—tying with the city’s coolest low temp of the season recorded yesterday.

It was frosty inland this morning with lows of 27 at Shabbona, 29 at McHenry, Rockford and Elwood; 30 on the ground of Midewin Tallgrass Prairie and 31 at Huntley and Naperville.  The arrival of clouds and moister air means tonight’s temps will be far milder.

A BLUSTERY, WET AUTUMN STORM SYSTEM centered late Wednesday over Colorado is headed toward toward the Chicago area.  The system is a slow moving and is to dominate Chicago’s weather through the coming weekend and into early next week.  TOTAL ESTIMATED RAINFALL is to reach to 1.50″ to 3.50″ range—making the multiday rain this system generates the heaviest to reach the Chicago area in the 3 months since early July.

Rain has been spreading north through Illinois Wednesday and will overspread the Chicago area Wed evening continue in waves overnight which could include some thundery downpours as warm, moist air runs up and over the cooler air to ride into the cool air delivered by gradually strengthening ENE winds.

Rainy weather persists in periods Thursday without the risk of thunder amid moderate ENE winds which will build waves over Lake Michigan—then thins out in coverage a good part of Thursday night.

It’s Friday and Friday night in which the moisture inflow appears greatest and rainfall may be heavy at times with embedded thunder a possibility again.  And rain is likely to continue into Saturday. 

The weekend is to find Chicago in a tight pressure gradient between the backside circulation of the eastbound storm and a broad area of Canadian high pressure.  The full-fetch (i.e. “full length of Lake Michigan”) and t 30+ mph wind gusts expected to develop are to churn Lake Michigan as vigorously as in any previous situation this fall.  This could build waves which top 12 ft.–so this WON’T BE THE WEEKEND to plan Lake Michigan outings.  What’s more temps riding these winds into the area as they sweep across the still warm waters of Lake Michigan set the stage for some lake effect showers Sunday and Monday. 


TONIGHT: Clouds lower and thicken, winds strengthen slowly and waves of showers and possible t-storms grow more numerous and potentially heavy at times.  Milder than recent nights. Low 54.

THURSDAY: Rainy spells, breezy and cooler. High 61.

THURSDAY NIGHT: More limited shower coverage—but showery spells are still likely at times. Cloudy, windy, mild and damp. Low 56.

FRIDAY and FRIDAY NIGHT: Waves of rain and possible thunderstorms with possible heavy downpours at times, fairly windy. Wind gusts to 30 mph at times. High Friday 64. Low Friday night 50.

SATURDAY: Quite windy and cooler with rain. Wind gusts to 35 mph.  High 57.

SUNDAY, MONDAY and TUESDAY: Frequently cloudy—peeks of mixed sun may occur, windy and cool. Some lake-effect rain showers possible. High Sunday 55. Monday’s high 54. Tuesday’s high 58.

WEDNESDAY: Some cloud breaks—but an overcast reassembles. Growing prospects for showers Wed night.  Milder. High Wednesday 62.