Monday, November 05, 2012

Coastal's Snowy Proposition?

The models have teased occasionally with the prospect of snow in parts of the region with the upcoming coastal storm -- but today's runs of the GFS and Euro both paint a stripe of white across the Delaware Valley on Wednesday afternoon and evening.

Yes, slightly more than a week after a hybrid hurricane, another coastal storm could torment the Delaware Valley and Jersey Shore with wind, rain, coastal flooding...and this time, inland, perhaps some to a decent amount of snow.

The burnt of the storm will be felt across the region on Wednesday afternoon into Wednesday night.  Modeling has come into pretty good agreement about a track close to the coast, with the the GFS and Euro within 30 miles of each other (and the GFS closer to the coast than the Euro at this point).  While track has been relatively consistent on the Euro, the deepening factor of the coastal storm and the amount of "cold" air in the atmosphere to work with has been varied on the Euro.  The Euro has been generally showing more snow but has generally aligned the track across Central and Northeast Pennsylvania.  Today's run nudged that the low track a bit east and has painted the heaviest swath along I-95 from Baltimore and suburban DC northeast through the Delaware Valley.  The Euro does show more snow in more places but the bullseye is generally Philly to Baltimore.

Temperatures aloft would be cool enough for precipitation to fall aloft as snow.  Temperatures at the surface will start in the upper 30's into the lower 40's on Wednesday as precipitation starts.  IF precipitation is heavy enough, that snow will make it to the ground as colder air aloft gets pulled down to the surface.  This type of snow would be the more "concrete" based snow and not the lighter, fluffier snow.  Think last October type snowfall ratios...lots of moisture in the snow, not very light and fluffy.  Instead of the usual ten inches of snow in one inch of rain, it could be closer to 5:1 with this event.  Regardless, to get snow to fall the key is intensity in precipitation and given the trend on the models for this storm to intensify the low more rapidly, the potential for snow is legit and at this point we gotta put consideration into a snow event occurring for some parts of the region.

The question comes down to where does any "thump zone" sets up -- the models are hinting at a swath along I-95, with the GFS coming in a touch west (it has a slightly more western track on the model at midday) or right along it to just east (Euro).  We're splitting hairs in terms of geography but this thump zone will be where precipitation falls a bit heavier, thus allowing for snow to reach the ground more effectively IF such a scenario verifies.  Some places could pick up several inches of snow from this before we're done.  Elevated areas, especially north and west of the city, could do really well in this event and pick up several inches of snow.

For those at the Shore, the wind is probably a bigger issue to be concerned over.  The Euro (above) shows 30-40 mph winds at the coast, with slightly higher gusts.  However, because the center of the storm is slightly east than the GFS, the strongest winds with the storm are farther removed from the Jersey Shore.  However, the GFS scenario has winds of 40-50 mph along the coast (sustained), with gusts to 60 mph since the center is closer to the coast.  Either scenario is not good and it will only exacerbate a bad situation at the coastline.  However, the Euro is "less" bad.  In both scenarios, some tidal flooding and beach erosion will occur but the GFS scenario is worse for the coast.

The snowy aspect is a big wildcard -- and not a lock at this point but as stated earlier, definitely something we have to talk about as a possibility.  Some places will pick up a few, perhaps several inches of snow.  Specifically where remains to be seen but the hilly parts of the region have a good shot of picking up more than those right along the coast or in the city...but even in those places, some snow can't be completely ruled out.

We'll have another update on this tomorrow morning.