December opens third-warmest since records began in 1870; only 1988 and 1954 warmer

 

The warmth of the past few days—–which is to be noticeably diminished Wednesday—has produced the third warmest December open in 142 years of official observations here.

 

The month’s opening four days have come in at 51.4-degrees, an eye-catching 18.2-degrees warmer than long-term average of 33.2-degrees dating back to 1871.

 

Only Dec. 1-4, 1998 (55.5 degrees) and the same period in 1982 (54.4 degrees) opened warmer.

 

Wednesday to tap into the reservoir of cold air to Chicago’s north and to see temps here sink to more seasonable levels

 

Chillier temperatures within the southern flank of a broad reservoir of frigid arctic air draped across Canada—much of it producing single digit or sub-zero temperatures —-has spilled into Chicago Wednesday. The cold has traveled over bare ground to reach this area, a development which promises to spare us the full impact of the bitterly cold air to the north. But, Wednesday’s high in the low 40s is to represent a 16-degree pullback from Tuesday’s near 60-degree warmth.

 

Happily, this cold punch is to be a comparatively brief one, pulling back as southerly winds take up residence here Thursday.

 

A more significant rendezvous with this cold air mass is to come later this weekend—one which may deliver at least sections of the Chicago area a cocktail of wintry precipitation which may shift to snow by early next week.

 

The season’s snow drought isn’t limited to Chicago; U.S. snowpack is running a quarter of the 10 year average

 

Snow’s been in remarkably short supply to date this cold season —and not just in Chicago.

 

NOAA reports the U.S. Lower 48 snowpack is a quarter the most recent 10 year average for early December.  Virtually every observation site in the Midwest is reporting less snow on the books that at the same time a year ago—remarkable because last season was noteworthy for its lack of snow production!

 

Only eight years join 2012 in seeing so little snow by now

 

Snow data for Chicago dates back to the 1884-85 cold season.  In all that time, only eight years have seen as little snow as has fallen this year. Just a trace of snow is on the books this season to date.

 

Interestingly, those eight snow seasons went on to produce sub-par snow tallies. It’s a trend which runs contrary to the tendency we discovered when surveying winters between La Ninas and El Ninos—which is what is predicted this year.

 

Almost two-thirds of those snow seasons ended up with above average snowfall.

 

More active pattern does seem to be coming together; model consensus delivers Chicago’s largest precipitation tally in nearly 2 months over the next week

 

A more active pattern, beginning this weekend and extending into the next two weeks, may help address the serious precipitation shortfall which has been observed thus far this season. Multiple computer model forecasts suggests an average of 0.97 inches of precipitation may fall in the coming week—some of it possibly as sticking snow.

 

If that amount does actually occur, it would be Chicago’s biggest 7-day water-equivalent precipitation total in the nearly two months since mid October.