Record warmth Monday, but a pattern change may be on the way

The numbers are in and two record high temperatures were set at the Chicago/Rockford Int'l Airport Monday afternoon.  The high reached 69° yesterday afternoon not only breaking the daily high temperature but also the all-time record high for the month of December!  The old daily high temperature record was 65° set back in 1970 and the previous all-time December record high was 67° set back on December 5th, 2001.  Quite an impressive day, if you ask me! 

But if you were to ask someone else they may say they're ready for the cold and snow and this wish might not be that far off.  As the atmosphere tries to balance itself out between the changing seasons we may have a couple stronger storm systems to watch for in the weeks leading up to Christmas.  Very cold air in Alaska and northern Canada has been 'cooking' while the lower 48 has been mild.  It looks as if some of this cold may be unleashed by early next week as a storm system moves down the British Columbia coast late this weekend and follows a stalled frontal boundary that will be draped somewhere in the Midwest.  It's with this potential storm system that some of the cold up north may be brought down.  Along with the added cold would also come an increase in accumulating snowfall.  As the clash of the different air masses, warm in the south and cold in the north, becomes greater so will the storm systems that try to balance everything out.  If we get just the right track, which would be low pressure moving from the Oklahoma panhandle into Indiana, the greater the chance is for snow.

Another factor that leads me to believe there will be a pattern change coming, although it's not definite, is the phase of the NAO (North Atlantic Oscillation).  When the NAO goes into a negative phase this tends to increase the likelihood of cold air intrusions into the Plains, Midwest and Northeast.  This change to negative appears to be around the 10th or 11th of December.  Now is this set in stone, NO.  Will there for sure be cold and snow within the next two weeks, NO.  But these are the types of signals we look at to help us try and better forecast longer term weather. -CK