Friday, February 17, 2012

Thrill of Snowless Victory, Agony of Snowstarved Defeat?

The upcoming snow event for Sunday is looking like it will pop someone really well.

That someone is Roanoke, not Port Richmond.

Computer modeling with the upcoming storm is, in general, continuing a southward nudge with the storm.  With the exception of the NAM computer model, no computer model in the region brings us snow as of late this afternoon.  The NAM is the northernmost of the modeling and a clear outlier compared to the GFS and European guidance, which has the storm system too far to the south.  Each successive run has weakened, slowed down, and pushed the system ever so slightly farther south thanks to the influence of a push of the northern jet stream in the wake of a weak disturbance that will cross our region tomorrow night.

The NAM, the most aggressive, has the track of snow grazing into Southeastern Pennsylvania, with a steadier and heavier swath of snow across South Jersey and Delaware down into the Delmarva.  It does bring a couple of inches into Philadelphia on the operational version of the NAM; however, no accumulations of snow fall generally north of the PA Turnpike or Interstate 195.   With this said, the higher resolution version of the NAM that I look at on Penn State's E-Wall site keeps measurable precipitation south of Philadelphia.  It's a pretty accurate look at the model, by the way, and sometimes "sniffs" things out before the main NAM does.


Comparatively, the GFS and EURO both keep measurable precipitation south of the city in general, with maybe a coating to an inch at most up to Wilmington or Millville.   The Canadian, another model that typically is a northern/stronger outlier, grazes the Philly metro with precipitation but keeps the steadiest push of precipitation south of the city.

The issue with the storm isn't the weakening trend or the slower arrival.  A weak disturbance in the northern jet will be crossing the region tomorrow evening.  This disturbance is currently over Minnesota, Wisconsin, and the Upper Peninsula of Michigan and pushing along to the east.  It will cross Pennsylvania and Upstate New York on Saturday.  Some of the earlier computer guidance suggested this disturbance going to dive south a bit more, phase in with the southern storm, bringing a more powerful system along to the East Coast that would yield snow and some rain.  Unfortunately for snow lovers, the northern stream system is moving along too quickly and the southern stream too slowly to bring the snowy result you want.    Assuming no dramatic shifts in thinking, the reality is going to be relatively snowless for much of the region.  South of town, you still have some hope at cashing in on a modest snowfall Sunday from midday on into the evening hours.

The best chances of accumulating snow will reside south of a Avalon-Dover-Washington line...an inch to perhaps three inches could accumulate down there.  North that to about Long Beach Island-Claymont-Kennett Square, you could see a coating to perhaps an inch of snow.  Operative word is "could" -- dry air in the lower atmosphere may prohibit you from seeing snow reach the ground and "eat away" at the storm's intent to push north.

A small nudge north could bump Philly into that coating to an inch department but any talk of blizzards, of one foot snows, ain't gonna happen.  This is, at best, a minor event locally and a nuisance event south of town.  North of the city, you'll be lucky to get much in the way of accumulation or even a snowflake from it.