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.