The calendar may say late January, but the weather says mid April. A huge push of record setting mild and moist air is over the center of the nation. The moisture content is from 3-5 standard deviations above normal for late January. This while a very strong and deepeing upper level trough is also moving over the center of the country. The two will combine to produce very heavy rain and widespread severe weather. A broad swath of the country is under the severe weather threat into tomorrow.
For the Chicago metro area it is truly record setting. At 7:00 a.m. O'hare had a temperature of 60, breaking the old record of 59 for the date. The morning dew point of 58 is higher than the normal high of only 31. Wow! This surge of high moisture was behind the band of thunderstorms that moved over the metro area last night. Hail to one inch was reported in some locations, along with local downpours, details here.
With extremely rare high moisture content in the atmosphere, and a 185 mph jet stream moving into the Midwest, the stage is set for possible severe weather and local flooding tonight. The computer models are producing from 2 1/2-3 inches of rain over the metro area through tomorrow morning. With the ground still frozen under the immediate surface, this rain will either lead to local ponding of water or rapid runoff into rivers and streams. Local flooding is definitely possible tonight into tomorrow.
Along with the flooding risk is the threat of severe storms over the metro area. While an isolated tornado can not be ruled out, I believe the main severe threat is high winds and large hail. The storms will be moving roughly at 60 mph tonight. It is easy for a cell to deflect some of the strong winds aloft down to the ground. Winds at roughly 2000 feet above the ground are forecast to be around 60 mph.
The warmth will be history tomorrow as much colder air moves in. Any lingering rain will change to light snow or flurries between 10:00 a.m. to noon over the metro area. Some minor accumulation is possible in the afternoon and evening over the city. The best chances of a few inches of snow looks to be from the far northwest suburbs toward Rockford and then northeast. Spring jacket today, snow blower tomorrow.
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