For the second year in a row, December’s putting on an incredibly mild face---rare in the annals of Chicago's observational record. The month's 41.5-degree average temperatures continues a stunning 15-degrees above normal and 8-degrees above a year ago.
The abnormal 50-degree temperatures predicted to grace the Chicago area Thursday and Friday are the equivalent of mid-November-level daytime readings and are 15-degrees above normal.
Howling south to southwest winds are to accompany the late season "warmth" by Thursday afternoon---though winds will ease markedly late Thursday night and Friday, only to roar back into the area Saturday.
Paucity of snow at this late date truly rare, matched by only two other cold seasons; 2012 running 9th-driest to date of the 142 years on record here
Snowfall, an essential component of Chicago's annual precipitation mix, continues to be a "no-show". 2012's paltry "trace" of snow currently on the books places the new season in rare climatological territory.
Only two of the 128 snow seasons for which official snow data exists going back to 1884-85, has produced as little snow by Dec 13---the 1965-66 and 2001-02 snow seasons.
Chicago's total precipitation in 2012 in running at scandalously low levels. Only 25.20 inches of moisture---rain and the meltwater from the snow combined---is on the books here. That’s a tally which is only 71% normal and 10.41-inches shy of historic norms by this date.
Total precipitation since Sept. 1 is even more sparse. Only 6.36 inches has collected in Chicago's official O'Hare rain gauge---an amount that's just 61 per cent normal!
Little wonder lakes and rivers are nearing all-time lows in many sections of the region. Lake Michigan's depressed water level appears on its way to tie an all-time December low, according to the U.S. Army Corps of Engineers Detroit Office, and it may break the lake's all-time low in the coming months thanks in part to the warm, dry weather which has dominated for such an extended period of time.
First 100 percent sunny day in nearly a month Wednesday; December continues Chicago's sunnier than normal trend
That Wednesday managed a 46-degree high isn’t surprising. The day was the first since Nov. 16 to receive 100% of its possible sun.
December has recorded 45 percent of its possible sun---more than the month's normal of 41%. If this trend continues, December 2012 may become the 15th straight month to exceed its normal monthly sunshine---another new record.
Bitter cold has Canada in a Deep Freeze; 0-degree temps within 680 miles of Chicago to the north
So where’s the bitter chill of winter? Alive and well across Canada, much of which has been plunged into a bitterly chilly arctic air mass---in places more than 30 degrees below normal. Temperatures dropped to 40-below zero in sections of Manitoba early Wednesday and 0-degree temperatures were evident as Wednesday opened within 680 miles of Chicago in northern Minnesota and North Dakota.
Cold can't advance south in the regime of fast westerly upper winds
The chill isn’t able to plunge south because upper winds are strong and westerly. Any cold air which attempts to surge southward is sheared eastward before it can make it very far into the Lower 48.
Southwest storm system to become Chicago's next precip-maker Saturday; model rain projections suggest it could generate more precip here than any over past 2 months
A Pacific storm, currently sweeping the Southwest, turns northeast into the Plains and Midwest in the days ahead, bringing Chicago much needed rain in the system’s “warm sector” Saturday.
An average of a suite of computer model precip projections hints that as much as 0.79 inches of rain could fall as an average across the wider Chicago area. If true, it would be the biggest rain event to occur since October.
The spread in individual rainfall forecasts used to develop the average of 0.79 inches ranges from 0.52 inches on the low end of the spectrum to as much as 1.54 inches on the top end.