Thursday, January 6, 2011

Of Models and Snow

Yes, there is an opportunity for a Winter Storm (4"+) category snow on Monday and Tuesday.  I will also tell you that the idea of getting buried much deeper than that is also on the table.  Before addressing the storm it is important to gain perspective about computer models.

Models are tools designed to provide possible outcomes from the interaction of known weather and climate variables.  They do not create weather.  As tools computer models actually do not forecast weather, real people do that.  The computer models are also using different algorithms with some performing better in certain situations that others.  Oddly enough the European model, the ECMWF, very accurately forecast the Boxing Day Knockout 3-7 days ahead but lost accuracy once the real system was over land and more data was available.  Other models depend on input of good data to get details about precipitation amounts, system structure, temperatures, and more correct.  The crazy model output leading up to Dec 26 was in my opinion a symptom of poor quality data than model performance.

Therefore let us not cheer model output that looks agreeable.  It is more fulfilling to praise the One who created the great mysterious systems of Weather and Climate which even the world's most powerful supercomputers seem to fall far short in processing.
Job 37:5-6 (ESV)
God thunders wondrously with his voice;
he does great things that we cannot comprehend.
For to the snow he says, ‘Fall on the earth,’
likewise to the downpour, his mighty downpour.
The Snowstorm

The Jan 10-11 system is not one that conforms to my system of watching tropical patterns to identify systems that will out-perform or a dramatic change in weather.  Oddly enough that particular date follows a period of high amplitude!  While I am not accustomed to winter storms following Fall and Spring rules (tropical peaks and valleys, not just valleys) you need to know that I do not see a big Winter Storm as being guaranteed.

I also expect the weekend to become agonizing as the storm comes onshore and its data gets fed to the tools called Computer Models.  My suspicion is that the same quality problems that plagued days leading up to the Dec 26 storm have not gone away.

On Satellite the storm has some interesting features:
  • A large upper level circulation.
  • Connection to a powerful subtropical jet stream which is extremely UNCOMMON in La Nina seasons.
  • Access to an abundance of moisture.
Below is a water vapor image from the University of Wisconsin SSEC. 
Upper Low attached to Subtropical Jet
The idea is that this system will cross the Northern Gulf of Mexico and join forces with the monster Arctic air mass and associated energy to spawn a storm that exits the US near the NC/SC coast.  If this scenario succeeds then there will be plenty of moisture for lots of snowmaking.  Unlike Dec 26 this storm cooperates with the Northern jet stream but does not phase.  IF this occurs then deep snows will affect a broad area of N GA, SC, and NC.  VA could get some in the south but escape a winter storm criteria.

This ECMWF illustrates the scenario very well.  Sometimes that model has trouble with timing systems emerging from the SW US.  If the system is late then the Arctic cold could push the track further south and leave even Central NC out of the running for a big snowfall.  Here is the possible outcome as depicted by the ECMWF.
A Scenario that would lead to deeper snow totals.
Expect more updates this weekend as the situation develops or fizzles out...

No comments:

Post a Comment