It’s the final weekend of meteorological autumn—the three month meteorological winter period gets under way NEXT weekend. The early read is that our coldest season may open on a fairly mild note.
But that's sure not the case Saturday. Just a day beyond the Chicago area’s near record 63-degree Thanksgiving high—the holiday’s third mildest temperature in 142 years of records—this weekend's temperatures are to get under way on a cold note!
Not only did readings across the metro area dive from a pre-dawn morning high of 42-degrees at 12:29 a.m. into the 30s, but once there, temperatures never recovered. Readings remained in the 30s in the midst of near 50 mph gusts the remainder of the day.
Friday’s howling winds produce wind chill temperatures which made the day “feel” 46-degrees colder than Thanksgiving
Peak gusts Friday hit 50 mph at Grundy County’s Carbon Hill, 49 mph Pontiac, 48 Gary and Harvard, 47 mph Midway Airport, 45 mph Hinsdale, 44 mph DeKalb, 43 mph East Chicago IN, 42 mph at Minooka and 38 mph at O’Hare. The combination of those gales and the steep drop in air temperatures produced wind chills in the teens. That put the change in the “feel’ of the air between Thursday’s 63-degrees and the 17-degree wind chill measured Friday on the order of 46-degrees!
Thursday to Friday temp dive the equivalent of nearly 3 months of cooling in a single 24-hour period
One way to visualize just how extreme the Thursday to Friday temp change really was is to compare each day’s temperatures to comparable normal highs and the dates which they occur. On that basis, the shift from Thanksgiving’s 63-degree high and Friday’s afternoon’s 31-degree reading was the equivalent of moving from the normal highs associated with October 15 to January 1's normal highs. It was like compressing the decline in normal temps distributed over that two and a half month period in a matter of just 24 hours—a remarkably rapid shift!
Areas of North Woods downwind of Great Lakes hit by up to 12 inches of lake-effect snow
The frigid air passing across the ice-free Great Lakes, which still boast relatively mild water temperatures, turned the “lake-effect snow machine” on "big-time" over sections of the Upper Midwest. Snowfall wasn’t uniform, but accumulations of 12 inches occurred at Cornucopia and Hawthorne—both in Wisconsin; 11 inches at Oulu, WI; 10.7 inches Bayfield WI, 10.5 inches Maple, WI; 9.6 inches Bergland WI and 9.5 inches at Mellen, WI.
Temperatures to moderate to more seasonable levels Sunday
Clouds overspread the area later Saturday and Saturday night as low level winds begin shifting south to southwesterly. The arrival of these clouds offers a clue that milder air is to be running up and over our cold air, which by Saturday night will be in retreat across the Midwest. Modest warming is to follow Sunday and into Monday.
Disturbance could swipe the area with a spell of late Monday/Monday night wintry precip
A disturbance, which appeared capable of a spell of cold rain or snow later Monday and Monday night has adopted a more southerly track on a suite of machine forecasts generated Friday. It may, however, still be capable of producing a period of cloudy skies and perhaps a fairly narrow ribbon of chilly light rain and possible ice pellets and/or snow Monday night with clearing now expected Tuesday.
Warming next weekend as meteorological winter gets underway
Warming next weekend wouldn’t be surprising. But, in the “we’re going to have to monitor this one” department, the two key cold weather indices—the so-call “NAO” for North Atlantic Oscillation Index and the “AO”, which refers to the Arctic Oscillation Index, are both predicted to turn “negative”. When that happens, cold air generally makes its way into the Lower 48 at some point. So while the new winter season may see a milder than average open, it wouldn't be surprising to see cold air wash back into the area at some point in the one to two week range. It's a situation worth monitoring.