The unseasonably mild, moisture-laden air, behind the thick, London-like fog which slashed visibilities to fractions of a mile to the west and north of the city overnight, is to produce temperatures more typical of mid-November than early December Wednesday. But warmth of that intensity is difficult to maintain this time of year. Only strengthening southerly winds, east of a developing winter storm in the western Midwest, make Wednesday’s predicted 56-degree high possible. It’s a temp out of place in early December when normal highs hit the 30s.
The unseasonably mild readings are to hold just beyond Wednesday evening. That’s when an arctic cold front crashes Chicago’s warm weather party and temps commence a dive leading us into an air mass likely to register the season’s coldest temps to date.
Though readings by daybreak Thursday will only have fallen into the upper 20s and low 30s in most sections of the Chicago area, they represent a huge retreat from the mild readings to which area residents have awakened Wednesday. It's a change which is unlikely to go unnoticed.
Temperatures in subsequent days will continue on a slow but steady downward trajectory so that by Saturday morning, when single digit and low or mid teens are likely to occur, readings will have come down 47-degrees off Wednesday afternoon's 56.
Wednesday to generate area’s mildest high in 2.5 weeks
A 56-degree high Wednesday would rank as the area’s mildest temp in two and a half weeks—since the abnormal 69-degree reading which helped fuel the devastating tornadic thunderstorms which raced, with deadly consequences across Washington and other Illinois communities, including Coal City and nearby Diamond.
First cold punch to be followed by a stronger one next week in the wake of a Sunday night disturbance which may produce a modest snow cover
Southwesterly steering winds continue above the incoming cold blast. That upper air configuration has been known to lift storm systems up the sharp temp contrast zone on the eastern flank of the frigid air masses like the one crashing southward into the Plains and Rockies.
Such a disturbance continues to be predicted by our medium range computer forecast models late this weekend.
The clouds and snow with such a system are to hold off until late Sunday and Sunday night, if the latest computer solutions prove valid. And, while not an especially prolific snow-producing system---at least as characterized by the latest model runs--- any cover of snow it might produce would no doubt be enough to facilitate the move of even colder arctic air into the Chicago area Monday and Tuesday next week.