Thursday, February 07, 2013

Finding A Snowy Ending

No need to name a will be memorable with or without a faux name attached to it.  It will be especially memorable for North Jersey, metropolitan New York, Long Island, and New England where blizzard conditions may occur near the coast and even inland in parts of Southern New England.

Locally, the storm will develop just as it reaches our area.  It's going to be a big, sudden, rapid intensification and it will lead to a significant thump of snow tomorrow evening across portions of the region.

This is a dicey storm to forecast across the region -- the fusing of a soaking southern storm with northern energy means a very sudden, quick thumping storm.  In many respects, it's similar to the thump storm of February 5th, 2001 that for many resulted in a commute from hell home from work.  Given the timing of rain to snow transition likely to be in the afternoon and evening hours, Friday night's commute home from the office will probably be a slow, arduous slog.

The bulk of the storm starts late tomorrow morning, mainly as rain in the city and points south but perhaps as a shot of light snow north of Philadelphia before a transition to a rain/mix in the Philly burbs and perhaps in the city itself.  Some modeling indicates it's rain, others a mix.  North of the city, that shot of snow will transition over to a mix south of Allentown and into the Philly burbs, remain all snow north of I-78.

After midday, the transition from rain to snow takes place from northwest to southeast.  It will probably take until the PM Rush to reach Philadelphia but most modeling indicates that transition reaches the city by 5 or 6 PM.  We will be mostly snow from the city on northwest around the dinner hour, with that changeover line pushing southeast steadily through the evening hours.  Rain increases in intensity for much of the region during the afternoon hours and will be quite heavy along the coast, with one to two inches of rain falling before the transition to snow.  Not only could there be some flooding issues down at the Shore, but then you'll have snow falling at the backend of this storm, leaving a sloppy mess behind.  Not a fun storm for the Shore, even if snowfall totals are modest down there.

Snow falls Friday evening, ending after Midnight west and around daybreak at the Shore.

IF the storm intensifies even more rapidly than the more aggressive models indicate (moreso than the Euro), the possibility for a quicker transition from rain to snow is possible.  From the midday modeling, the Euro suggested about 6" of snow, the GFS and NAM suggested three to four on the back edge in the city.  Three to six inches for the city is a reasonable benchmark to work within.  If we pick up more than 1.5", it will be the season's largest snowfall at the Airport.

The gradient on snow will be significant and sharp -- an inch of snow is possible in Kennett Square while Trenton could, conceivably, see around 10" of snow (we have them in the 7-13" range).  The gradient just so happens to fall right across the Philadelphia metro, with snowfall totals varying quite a bit from southeast to northeast.  This will be due to the storm's intensification, wrapping moisture around the back edge of the storm, drawing in additional cold air, and the storm pulling northeast as it does so.  The intensification process happens too late for DC and Baltimore...and for the snowstarved, they would argue it's too late for them too south of the city!

That said, 50 miles makes a ton of difference with this storm from a geographic perspective...and our feeling is that the meteorological "boom" takes place just northeast of the city, with a foot of snow possible from Central Jersey on north.  Parts of New England could see two feet plus from this storm.

We'll provide another update on the storm tomorrow morning as it approaches the region.