Chicago is two days into a new month and heading into its eighth consecutive day likely to post a temperature deficit. The sub-normal temperature trend marks the continuation of a cooler than normal temp regime which first took up residence here in September. The cooler than average spell brought an end to a record-breaking, uninterrupted 11 month string of above normal months. And, although sharp warming is predicted to occur for at least a time starting a week from this weekend, there's little about the current pattern to suggest temperatures will be much different than where they've been of late going into a good part of next week.
Greenland blocking pattern responsible for deflecting devastating Sandy into the East Coast remains stubbornly in place ; it's a factor behind the chill here
Stubborn blocking over Greenland and the North Atlantic is still front and center---a feature whose importance can’t be overstated in the meteorological events of the past week. The current blocking pattern has played a seminal roll in turning Sandy westward and into the Mid-Atlantic and is contributing mightily to the chill we are to face through the weekend and into next week.
The blocking effect is produced by a sprawling dome of warm air aloft which affects upper-steering winds. The warm air also dispel;aces cool air normally in place over northern North America, forcing it bodily south into the Lower 48 where it remains effectively trapped for an extended period of time.