Friday, December 24, 2010

Christmas/Boxing Day Storm shifted east

Merry Christmas Eve

The time is now coming upon us that we see what actually happens with the snow or lack thereof.  As many of you know the projected storm path has shifted east and by now seems supported by the weather map.  Most likely Central VA will see little or nothing.  Parts of eastern NC who are used to helplessly watching snow falling on their western neighbors appear to be the likely big winners of White Christmas, albeit late in that day.

While I do not want to cause false hope there is good reason to watch the weather over the next 48 hours because uncertainties while tending to dry up or melt Raleigh, NC snow can go both ways.  Also, a 75 mile shift west would be a major difference in snow values.  Here is the current water vapor image from University of Wisconsin SSEC:
The basis for a weaker storm that is out to sea is that convergence
takes place offshore.  The -NAO Block may be suppressing the system
too far south.  The southern storm does have a well defined circulation.
What could shift the snowfall outcome would be how the swirl of cyclonic energy in the southern storm might indicate strength not accounted for in the models.  Other than that the strong blocking pattern that has froze us this month remains very far south and probably the biggest argument in favor of the eastward shift of the snowstorm.

What can we expect? 
  • Central VA is free to celebrate Christmas Day without concern about snow covered roads ...etc...   Do keep one eye on events to the south.  I will keep you posted on possible Boxing Day light snow.
  • Accumulations in Eastern NC (I-95 and NE Piedmont) may be impacted by rain.  If all snow would be close to 6".  I would project 2-6" the wide range attempts to account for the rain.
  • Raleigh Area mostly benefits from the Northern Storm's snow and will probably break the Christmas Day record of 0.4".
  • NC Highlands receives major Great Lake effect snow which they already know from experience will vary widely in accumulations.  6" is not out of the question for Boone.
This is definitely not my proudest moment as a Forecaster to have to back off of what appeared to be a huge snowstorm that would make history along the east coast.   If this was not Christmas weekend I would probably be thrown in the doghouse!

It is a concern that the European Model (ECMWF) which is favored for its accuracy and superior science would consistently tout a major snowstorm then change with just over 48 hours to go.  Three days of consistent output combined with a favorable weather map definitely led me to believe that this was the real deal (but check the weather often!). Perhaps the climate disfavor for December snow in Central NC is the ultimate variable?

I do have some lingering concerns about the whether the small area of precipitation coverage ahead of the cyclonic swirl might be concealing the true strength and impact of the southern storm.  It is not my expectation that another posting would come later about the big snowstorm being for real BUT... you can count on me to keep watching the system.

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