Moderate chill accompanies sun's return in a December running even warmer than last


Were winds northwest, the ground covered by snow and sunshine not as abundant as it’s predicted to be, the weather greeting Chicagoans Tuesday would be far different . But winds aren’t northwest—they’re southwest— and the ground isn’t hidden by a foot of snow, the way it is in areas to our north near Minneapolis.


The darker colored, bare ground still in place in Chicago Tuesday, will heat more easily which, in turn, will heat the air above it. That the day’s winds are southwest—not northwest—means the air blowing into Chicago won’t originate over the chill-preserving snow to our north. All this assures we have a day of 30s on the way—not the teens or 20s which will occur farther north.


It’s not obvious to Chicago area residents. Heavy snow accumulations occurred to our north over the weekend. All residents in this area saw in terms of snowy weather were brief bursts of mainly light snow and flurries late Monday. In combination with some drizzle at some locations, a treacherous layer of “black” ice formed across on some roads, particularly across the southern suburbs..  Late Monday’s icy road surfaces led to a number of traffic accidents near Peotone and rendered overpasses and bridges particularly vulnerable to ice formation. NO residual ice-inhibiting chemicals were on these thoroughfares because of the lack of snow thus far this season.


Late-day and nighttime lake effect snows swept into sections of northwest Indiana and southwest Lower Michigan, laying down as much as an inch, producing dicey travel conditions in those areas as well.


This past weekend’s snow system more than quintupled (multiplied by five times) the area of the Lower 48 beneath a cover of snow from Montana across a wide swath of the Midwest.


NOAA reported Monday that 31.9 percent of the Lower 48 had snow covering the ground—-up from barely 6 percent only last Thursday.


December 2012 a stunner: Temps running 15+degrees above normal; seasonal snow here still just a trace


No matter how its temperatures and lack of snow are examined, December 2012 is turning out to be one for the books—a real stunner!  The 43.2-degree temperature after its opening 10 days ranks 5th-warmest of any Dec. 1-10 period of the past 142 years, placing it among the warmest 4 percent of all Decembers in Chicago’s climate portfolio.


The month has managed a stunning 15.4-degree surplus to date and has bested last December’s open—which was no “shrinking violet” in the mild weather department itself—by 9.7-degrees.


Bare ground here and fast west to east upper winds holding bitter chill draped across Canada at bay; 50-degree high not out of the question by Thursday in Chicago


The fast west to east upper steering winds in place will continue the remainder of this work week to shear any bitterly cold air off to the east, before it’s able to gain a foothold in Chicago. The chill to our north is extreme and included a high of 44-below in Canada’s Yukon Territory Monday.


Greenland blocking in place—but strong westerly jet along its southern flank overpowering chill’s attempt to head south


What’s remarkable about the current pattern is a “Greenland block”—typically a cold signal for Chicago and the Midwest—in in place.


It should be noted bitterly cold air did seep southward into Minnesota over the fresh cover of snow Monday holding some temperatures there to single-digits with wind chills at double-digit levels below zero. But with strong west to east upper steering winds in place, that cold air was unable to advance south.


Fast jet stream to keep active weather systems racing off the Pacific and across the country; this past weekend’s system was the first in a series expected to continue over the next two weeks    


This past weekend’s storm system, which produced rain in Chicago and heavy snows to the north Sunday—and the rain-producing system here Friday night into Saturday, are but the first in a series of  eastbound disturbances—if not full blown storm systems—our computer models are moving across the country in coming weeks. It’s a development which could signal a boost in precipitation—which is sorely needed in the drought-ridden Midwest.


Saturday system looks like a chilly rain-producer; colder surges to drive 1-2 week temp trend lower; at least some systems in cooler regime could be  snow-maker


The next system hits later Friday night or Saturday. It’s rain/snow line is currently predicted to be just north of Chicago, keeping the city in what is likely to be a chilly rain. But an alteration in this system’s track could require a re-evaluation of the form the weekend precipitation may take and later forecasts should be monitored for any updates.


Half of the six winters with Chicago’s latest occurring snow have posted significant overall temp surpluses; the other half have averaged near the long term average


The nature of the coming winter, given the late arrival of cold air and snow, may not be as first thought. Early statistical work we carried out in-house suggested the winter and cold season of 2012-13— occurring as they are between El Ninos and La Ninas in the equatorial Pacific (in other words, what are known as “ENSO neutral” winters in the world of climatology)—might be expected to produce more “typical” winter temps and potentially more snow than last year, which turned out one of the mildest and least snowy seasons on record here.


But the open to the 2012-13 cold season has been anything but truly cold. Nor has it been snowy. Only a trace of snow has fallen to date—one of only a handful of years to have seen so little snow by mid-December.


Using past seasons which have produce their first snows as late or later than this one—there are six such seasons we identified—several trends emerge.


Half of the six produced markedly milder than average winters while the other half were actually within fractions of a degree of normal. Snowfall was lower too—coming in an average of 33 percent less snow.


Having said that, each season produced significant snows—in some seasons a series of them.


The 2001-02 snow season generated snows of 10.7 and 10.5″ while the 2011-12 season produced 7.7″ and 6″ totals.


The sample of snow seasons examined here is a small one which suggests the totals examined quite likely lay out only the barest outline of what may lie ahead. There are  rarely dull moments when it comes to Chicago’s winter.