Chicagoans to shiver through meteorological autumn 2012's third day in the 30s

 

Chicago temperatures, which dipped into the teens for the first time in the 9 months since late this past February, will struggle to reach the mid 30s Tuesday.  It’s to be only the third time this meteorological autumn in which highs have moved no higher than the 30s.

November 2012 is running 4.8-degrees colder than a year ago, though the month’s average temperature is close to normal. Below normal temperatures have occurred on 62 per cent of its days.

 

Slow temperature rebound begins Wednesday;  accelerates over the weekend as December arrives; unseasonable 60s possible Sunday and Monday

  

A slow temperature rebound begins Wednesday then accelerates later this week and into the coming weekend. The departure of arctic air and an incoming surge of maritime air of Pacific origin, is to drive the temperature recovery.

 

Evidence is growing that 60-degree temperatures are on the way Sunday and Monday, when southerly winds transport moister Gulf air into the region.  That process, expected to begin in the days ahead, is behind expectations that a good deal of cloudiness, haze and even some fog and drizzle may accompany the transition to milder temperatures by Thursday nighty and into Friday and Saturday. The warming is expected to culminate in October-level 60s Sunday and Monday—readings well in excess of 20-degrees above normal.

Nearly a third of the past 142 years have produced late season 60s

 

Temperatures in the 60s pepper Chicago’s cold season landscape more often than you might think. An in-house analysis of early season warm spells puts historic probabilities of readings at that level at 29%. And, interestingly, a scan of the city’s entire official observational record back to 1871 indicates 92 percent of all winter seasons have hosted 60-degree readings at one point or another.

 

Indicators turn decidedly colder next week with Greenland Blocking pattern’s development next week; December’s opening week to open warm and close decidedly colder

 

The transition from unseasonable 60-degree warmth to much colder air next week may be a sharp one. The shift is to be driven in part by the development of a Greenland blocking pattern comprised of a mammoth-sized pool of warmer than normal air there which tends to send cold air cascading into the eastern two thirds of the U.S.

 

Three of the four runs of the Weather Service’s “GFS” computer forecast model generate sticking snow at some point in the 8 to 14 day period

 

It’s certainly not a forecast yet carved in stone, but the fact three of Monday’s four runs of the National Weather Service’s GFS model kick out measurable snow in the Chicago area is of interest. That forecast can change. But our experience with this model’s handling of sticking snowfall suggests the odds of snow actually occurring here increases once snowfall is predicted by multiple runs of the GFS model. We’ll keep you posted in the days ahead.

 

 Potential for sticking snow later next week wouldn’t be surprising

  

Some sticking snow next week would dovetail well with weather history here. While measurable snow has historically occurred on or about Nov. 16, the first 1″ or more of snowfall has most often occurred on or about Dec. 3.

 

Mammoth area of drought in the U.S. without precedent; barge traffic on Missisissippi could grind to a half south of St. Louis after Dec 10 because of low river levels

  

More than 60 percent of the Lower 48 U.S. is in drought with Great Lakes levels down (Lake Michigan hovers just 1″ above its all time record) and rivers, like the Mississippi, running low as well.  It’s estimated barge traffic from St. Louis to Cairo may have to grind to a halt by Dec. 10 if no additional rain is forthcoming. Nearly 60 percent of U.S. grain exports reach the Gulf of Mexico by barges moving down the Mississippi.

 

U.S. farmers produced 13 percent less corn last year because of the drought even though they planted the most acres of corn since 1937.