Tuesday, February 12, 2013

In Line For A Few

Last night's modeling, in general, had a weaker system for tomorrow night although aloft there are still some pretty decent differences between the three models in consistency of the system's evolution. The GFS, in general, has been more consistent with the system's evolution aloft although timing varies a bit from run to run.  In general, these differences are minor but they will impact where the band of most snow falls in tomorrow night's system.

One thing that may occur with this system is a bit of rain at the very front end in a chunk of the region.   Daytime temperatures tomorrow probably get to around 40 in the city before precipitation starts.  Even if the models are a touch on the warmer side, I do think some rain is possible out of the gate initially.  It's not going to ruin the whole of the event but the lower atmosphere will need to cool.  Rain will gradually transition to snow, probably first in the areas where precipitation is falling heaviest (allowing the air aloft, which is colder, to pull towards the ground and cool the atmosphere off) and then shift southward through the evening as temperatures cool with precipitation.  Might start as snow in the hills and places where elevation is your friend but in the city I can see a brief rain to snow scenario setup as this moves in during the evening rush hour.

The NAM, which isn't necessarily gospel with its evolution of the storm system from a track standpoint, may have a decent handle on the various elements of the storm in terms of precipitation type and shows that transition from light rain initially changing over to snow as the system develops and intensifies.  The graphic above and below show that transition from 7 PM (above) to 10 PM (below).

The timing consensus from the models shows this moving in during the evening rush hour, changing to snow during the evening, steadiest and heaviest snows likely between 8 PM and Midnight. With a dynamic setup at work here, there will probably be a band or two of snow that tends to outperform and areas where snow may not perform to expectations...the general consensus is this band sets up near I-95, with some modeling south and others along or to the northwest.  There will probably be more rain and less snow initially at the coast due to temperatures being milder initially down at the Shore but even down to Cape May or Wildwood a coating is possible.  A shift of 30-50 miles changes who gets the most snow...if there were a shift it may end up being to the south and southeast in the end to where South Jersey and Delaware would benefit. As of now, we're keeping the higher accumulation potential overhead...for now.

The thinking now is that 2-4" is possible from about Gettysburg to Belmar, plus or minus 20 to 25 miles either side of that line.  Again, this could shift south or southeast but we'll wait until tomorrow morning before making any jumps and changes in our thinking.  One to two inches generally north of AC to Dover and south of I-80 outside of the two to four inch zone. It wouldn't shock to see some spots outdo four inches...this is a dynamic system that could create some pretty intense bands of snow assuming things come together just right.  However, consistency is needed in placement of the snow bands and impact before we lock in the "highest" possible totals and placement of those totals.