Cool surges accompany fall-like temps this weekend

FIRST, THE THURSDAY WEATHER HEADLINES 

—FREEZE WARNINGS HAVE BEEN HOISTED IN MANY SECTIONS OF THE GREATER CHICAGO AREA–ESPECIALLY AWAY FROM LAKE MICHIGAN TONIGHT—-Temps will drop off as clouds break overnight. 

–Clouds and showers have developed in a VERY UNSTABLE ATMOSPHERE over the Midwest. An “unstable atmosphere” is one in which the air aloft is so cold, temps drop faster than usual with height. This encourages air to rise which is why clouds have formed as Thursday’s sunny start. 

–Along with the clouds, some showers have formed and have been rotating in a counterclockwise fashion around an immense autumn low pressure centered on the western shore of Canada’s Hudson Bay. The system is SO large, it’s generating a wind pattern which extends from Montana east to the western Atlantic. 

–It’s SO cold aloft Thursday–small hail has been noted with some of Thursday’s rain showers. While temps are in the low 50s at ground level Thursday afternoon, temps a mile aloft are closer to 27-deg. That means snowflakes and ice pellets are forming in the clouds–and while most melt falling into the above-freezing air here at ground level, a few taller clouds–one or two which have produced isolated flashes of lightning, produce enough precip for some ice to make it down to the ground. 

–Clouds are likely to scatter tonight amid chilly temps only to start the day with mixed sun and yield to additional cloud development and some widely scattered showers, some with possible small hail, to re-develop with daytime heat Friday afternoon. 

—-Showers are to ebb Saturday but may form again Sunday, Monday and Tuesday afternoons. They’ll be scattered but still popping up across parts of the area. 

–Only 4 of the coming 15 days will be AT or ABOVE NORMAL. This will is to average 52-deg—5-deg cooler than last week. But NEXT WEEK is to be even cooler averaging nearly 9-deg below this week and likely to come in nearly 10-deg below normal. Northwest upper winds are the reason for the chill–and the persistence is only to ebb next weekend—that’s a week from this weekend—and spill into the following week. Temps at that time may surge near to modestly above normal. 

—As mentioned here yesterday, don’t be surprised to hear snowflakes are spotted in coming days and into next week in the Upper Midwest–possibly sinking farther south with chillier air’s arrival next week. LAKE MICHIGAN waters remain in the low 60s, though they’re coming down slowly. This will be enough to thwart major lake snows. But as some lake effect showers move inland in lower Michigan, some flurries can’t be ruled out there early and mid next week. 

HERE’S THE LATEST CHICAGO METRO FORECAST 

…..FREEZE WARNING AWAY FROM LAKE MICHIGAN LATER TONIGHT from 1 to 8am FRIDAY MORNING 

TONIGHT: Early scattered showers, a few with small hail, thin out. Clouds break, colder. Wind ease–but remain elevated averaging 7 to 17 mph. Low 36 in the city–but upper 20s or lower 30s inland. 

FRIDAY: Mixed morning sun gives way to more clouds and the return of some scattered rain showers–a few again with possible small hail. Becoming windy and cool. high 55–a temp 9-deg below normal. 

FRIDAY NIGHT: Clouds scatter by late, cold and breezy. Low 35–but closer to 30 inland. 

SATURDAY: Partly sunny and cool. High 54. 

SUNDAY: Mixed sun to start–but clouding over, breezy and cool. Several scattered afternoon showers possible. High 53. 

MONDAY AND TUESDAY: THE SEASON’S CHILLIEST TEMPS YET and the coolest readings and first daytime 40s since late April. Mixed sun gives way to cloud spells at times each day. Lake effect rain showers possible in northwest Indiana–and a few spotty showers may occur afternoon hours elsewhere. Highs Monday and Tuesday 46. 

WEDNESDAY AND THURSDAY: Remaining cool and breezy with sun and mixed clouds, especially afternoons. High Wednesday 47. Thursday’s high 55.