Wednesday, February 13, 2013

Nudging Our Snowfall Around A Bit

Winter Weather Advisories are out for the city and immediate suburbs, plus east to Ocean County, for tonight.  There isn't a ton of difference in thinking on specifics over the detail of the event -- showers to start, a transition from rain to snow during the evening, ends as snow for a chunk of the region.  That said, we've been able to get some consensus in place (outside of the European model) on where snow falls at the steadiest clips and are making adjustments based on that.

I'm going to use the NAM as a guide here because the graphics in high res mode are pretty good and higher resolution modeling should be able to get the key points across about this event -- the potential for quick developing, steadier snows in a narrow area, and how the changeover from showers to snow showers takes place.  The graphics below are from 10 PM this evening.

Above, you can see where precipitation is falling regardless of precipitation type.  The heaviest precipitation is in Ocean, Monmouth in New Jersey and in Southern Delaware.  The difference is that the New Jersey precipitation is snow, the Lower Delaware precipitation is rain.  The NAM, which had been very aggressive on snowfall a day ago, has trended back to a general 1-3 type event but its higher resolution is sniffing out the potential for that steadier, heavier band of snow across Central Jersey -- and that's the location where we think any of the three, perhaps plus inches could fall.  The RPM, similarly based off of the NAM in terms of its general programming, tends to show the same viewpoint and is showing a four inch swath across parts of Central Jersey.

The GFS is a bit farther north and northwest with the placement of the snow band but generally has the steadiest amounts (two plus) near the coast in North Jersey as opposed to across Central Jersey.  The GFS has been anything but inconsistent with its handling of the system so far.  We'll see if its right and the precip placement ultimately comes north.   The European computer model is pretty much a minor event for Central and South Jersey, maybe an inch or two at best...but given how inconsistent the model has been I can't get too behind its thinking regarding this event.

As this storm system moves through tonight, it will intensify in the Atlantic, which sets up the band of steadier snow as precipitation intensifies.  This results in a potential area of two plus inches, perhaps as much as four , in parts of Central New Jersey.  I've generally extended the two plus areas west to Mount Holly down to Long Beach and north into Monmouth County.  For Philly and the immediate burbs, I've nudged the totals down a notch to one to two but think some areas can coax three inches of snow out of this.  The outer north/west burbs should be good for an inch but the precipitation on this storm doesn't quite get going for you in time.

South of AC-Dover, it will be mainly rain that falls although some snow at the end could get you a coating or dusting in spots.

Changeover from rain to snow takes place after 7 PM tonight from north to south, with showers (rain) starting after 5 PM, helping cool the atmosphere and helping key in that changeover to snow. Snow ends around or just after Midnight.  It will not be snowing in the morning rush tomorrow.