8:00 AM

Every once in a while, well okay more than that lately, the model guidance likes to defy basic physical laws.  This morning, we have that occurring in the GFS, ECMWF, ensemble, CMC, and pretty much every guidance I am looking at.  Quick!  Get the doctor!  The models have the flu!

In all seriousness, the problem with the model guidance can be found at 500 MB and is perfectly described by DT from WXRisk on the Stormvista weather boards last night.  Basically, the problem with these models is that they produce a strong 500 MB upper low over southwestern Canada and another weak upper low over Ontario.  As the models continue later in the period, the 500 MB low over southwestern Canada moves to the Great Lakes, just as a strong 50/50 low is in place.  The problem?  Two large and strong upper low can not be in the same general area at the same time.  One of those lows have to give way and leave.

The development of this upper low over southwestern Canada impacts the potential storm for this weekend and for next week.  Initially, the upper low would lead to a zonal flow over the United States as the upper low crushes the ridge around Montana.  The result is that the Arctic cold front is held back and the Sub Tropical disturbance is relatively weak and flat.  That’s followed with the upper low moving east, cause a large ridge in the east and an exit of the Arctic air in the east.  All of this based on an idea that would argue against physics.  Further, the model guidance has been pretty bullish this month of putting a 500 MB upper low around British Columbia only to fail to do so.  Remember, at this point in the guidance 5 to 7 days out, the ridge over Alaska was supposed to be crushed with a strong upper low pushing the ridge into western Alaska.  Then there is reality.

So the natural question is where do we go from here?  Well, the best thing to do is to look at what is going on now and use a bit of common sense.  We know that a very cold air mass is on the way once this morning’s snow/rain storm exits to the north and east.  Temperatures will struggle in the 30′s for highs by tomorrow afternoon, a marked difference from the past few days.  We also know that the Sub Tropical jet stream is starting to act up.  Note the building moisture over Mexico, western Texas, and the Southwest.  Strong disturbances are racing east via a strong Sub Tropical jet stream.  We know that an Arctic disturbance will be diving south and a negative NAO 50/50 low will be in place.  The negative NAO feature is going to force the Arctic disturbance to move south and east towards the Mid Atlantic.  The question is whether that disturbance interacts with the Sub Tropical disturbance over the southern Mid Atlantic, off the New Jersey coast, or over the Canadian Maritimes.  That question is an unknown.  However, there is very much a threat for a moderate to heavy snow event from this low give these factors.  My concern is that the Arctic air mass interacts with this coastal low which will cause temperatures to crash on Saturday night/Sunday morning, which will ensure not only an all snow event but also reek havoc with the forecasting of snow ratios.  So clearly there is a lot of mystery to the time period of Saturday night through Sunday.

A strong cold air mass takes hold once again for Monday and Tuesday.  If one considers that the upper low over the southwestern Canada is a false idea, then the focus of the Polar Vortex is over Quebec which sets up the potential for another major winter storm for the Wednesday through Thursday time period.  Another strong Sub Tropical Disturbance will interact with a Polar/Arctic disturbance leading to another very impressive winter storm for much of the east coast.  The presence of an arctic air mass ahead of this storm and a strong Arctic high pressure system (1032 MB on many 12Z 12/8 guidance) would suggest a major snow storm is possible.

So to wrap up my thoughts for this morning.  Throw out the 00Z guidance not because it is warmer (cause I know some will accuse me of that) but because they defy the basic laws of physics.  Some bad data must have gotten into the guidance somewhere for all the models to be this wacky.  Keep your guard up for this weekend and next week.  Timing is everything and we probably won’t get the details we all want until 2 or 3 days away from the event, if we are lucky.