By Tom Skilling
Rain’s fallen into sub-freezing air across the northern suburbs overnight. The result has been” glazing”—a process which leads to the build-up of ice on untreated outdoor surfaces.
The icy conditions extend north from counties bordering Wisconsin into the Badger State itself.
Clouds and sporadic light rain and drizzle are to extend into Friday producing what promises to be a damp, raw day with temperatures close to historic norms.
To have “near normal” temps is quite an accomplishment in a month running nearly 6-degrees below normal and 17-degrees colder than a year ago!
The icy far north suburban locations follow the area’s highest daytime temperatures in 2 weeks
The ice follows the Chicago area’s mildest temperatures in 2 weeks Thursday. Residents near Midway Airport reveled in low 40-degree temperatures, a daytime high which was nearly 10-degrees above normal.
Thursday’s 39 and 33-degree extremes at O’Hare produced an above normal temperature for they first time in over two weeks.
A more significant winter storm threatens heavy, possibly flooding rains south and accumulating snow here and north Saturday night into early Sunday
Winter storm and flood watches have been posted for sections of the Chicago area for the coming weekend in anticipation of a potent weather system expected to lift from Texas into Indiana. That’s a track forecasters take quite seriously because it’s been known to bring the region heavy snow.
The more than inch of rain expected to fall on the area’s significant snowpack plus the potential for milder temperatures to contribute to the break-up of ice on area rivers, is to increase the potential for flooding late Saturday and Saturday night, particularly in southern sections of the metro area.
When ice breaks up on area rivers, it can lead to dams of accumulated ice on rivers behind which water accumulates.
A predicted transition to snow has been accelerated by overnight computer model runs. This means it could be snowing in the city by late Saturday night, around the time the northeast-bound storm is generating the maximum upward vertical motion in the area. It’s a set-up which may lead to heavy snowfall—even isolated thundersnow.
This further suggests sections of the Chicago area will register a significant accumulation of snow by daybreak Sunday. Snowfall then tappers off and frigid arctic air stages a come-back which sets Sunday’s temperatures on a downward spiral to single-digits Sunday night.
The arctic chill is to produce a cold open to Christmas week.