Wednesday, February 06, 2013

Winter Storm Watches For Central & North Jersey

Winter Storm Watches are out for Friday afternoon and night for Mercer, Monmouth, and counties to the north in New Jersey, plus Northampton and the Poconos in Pennsylvania, with the potential for several inches of snow to fall from a rapidly intensifying coastal storm that will develop on Friday off of the Carolinas.

As we've been saying, this is a mashup of precipitation, with Friday night's event the big part of the storm, especially north and northeast of the city where the storm's rapid development will bring heavy snows to them.  For most of the rest of us, the storm will provide a bit of everything but the heaviest snows will miss, perhaps by as little as 50-75 miles from the city based on current projections.  A faster, more rapid development may change this but it's not likely at this point.

Essentially, the storm is a three phase event -- light wintry precipitation early Friday morning before work starts up -- could be light snow or freezing drizzle, enough to cause some slick spots around north and northwest of the city.  This is in advance of the southern energy.  As the day progresses, milder air aloft and the surface nudge the precipitation type over to light rain for Philly, points south, and up to Allentown, with snow or a mix north of that.   By evening, the southern energy develops further and colder air draws back into the storm.  This will change that mix to snow north and with heavier precipitation working into the city we will see rain become heavier across the region, perhaps beginning to change to snow towards dinner from northwest to southeast.

Friday night is when most of the snow will fall in our region, likely after 5 PM.  The NAM, below, shows a mix changing to snow scenario but it's more likely that there is no mix zone locally -- it'll change quickly from rain to snow in the region as this storm intensifies and that heavier precipitation cools that atmosphere.  The result will be a quick, rapid changeover around the region form Philly on north.  The problem is that precipitation probably will be wrapping up in the city just after the transition takes place, meaning the snow period will be short and the thump of snow brief.   An inch or two is the most likely scenario in Center City.  The farther north and northeast one is, the longer you will get snow and thus you will get higher accumulations.  A slower to develop storm will result in lower accumulations for all of us...especially for those to the north and northeast...but as of now odds favor the storm developing close and quick enough to thump the northern half of New Jersey pretty good.

How much?  We're not going to top off these totals until tomorrow night but the general thought is the city is in line for an inch or two in the southwest half, three inches in Northeast.  The 5" zone is generally from Trenton on north and right along the Delaware River north of Trenton into the Poconos.  10" or more is likely north of New York City.  Some of this may be nudged around a bit tomorrow but there will be a very sharp, sudden cutoff in snowfall around parts of our region...the thought as of now is that it sets up along the Northeast Extension and just east of that.

We'll have another update tomorrow morning on this storm.