It has been a transitional winter so far -- with temperatures soaring into the 50's only to be followed a few days later by some light snow, and then another warm up. However, the end of this week into this weekend looks to offer something at least slightly different as a somewhat wintry pattern will continue for more than two or three days. Behind an average pattern in place through early Friday, polar air will be lurking to our north. And as energy from the southern stream of the jet ejects northeast and interacts with a piece of the Polar Vortex, a storm forming well offshore could touch off some moderate precipitation over our area. The forecast models have been struggling mightily with the interactions and strength of both the northern and southern stream energy -- and as a result have been inconsistent in their forecasts for our area. However, the bottom line seems to be this on all guidance: the storm system won't rapidly deepen until it is off to our north and east, which means our area should be spared any real heavy precipitation. That being said, the potential for light to moderate precipitation amounts..falling as snow.. does exist. Given these light amounts on forecast guidance, and factoring in some precipitation-type issues early in the system (before a change to snow), our general forecast calls for 1 to 3 inches of snow throughout the area. Pictured right: Our Storm Total Snowfall Forecast map...which shows the forecast snow accumulation through Saturday evening. 


7:00 - 10:00pm Friday: Skies become overcast, the potential for some showers or flurries across portions of southwest New Jersey.

10:00pm Friday - 1:00am Saturday: Light snow begins across much of the area, moving from southwest to northeast through the area. Precipitation could begin as rain at the coast, and even a rain/snow mix in some locations slightly inland from the coast.


1:00am - 4:00am Saturday: Light to moderate snow continuing throughout the area, with a rain/snow mix likely still continuing near the coast. Accumulations begin to occur on some surfaces.

4:00am - 7:00am Saturday: Light to moderate snow in all areas, probably even down to the coast. Precipitation will show signs of wrapping up in southwest new jersey. Moderate snow over New York and Connecticut.


7:00am - 10:00am Saturday: Precipitation begins ending from southwest to northeast over New Jersey, but continues over Northern parts of the state. The snow continues also over Long Island and Connecticut.


10:00am - 1:00pm Saturday: Precipitation ends over most, if not all, of the forecast area.
WHY LESS SNOW NEAR THE COAST?

A quick note regarding the precipitation type problems -- these are a result of the antecedent airmass which is in place as the storm arrives. It's no secret to anybody living in this area that we have had a lack of real "winter" air (or polar or arctic air, if you want to get technical). The reality of it is, that temperatures could be in the upper 30's to near 40 along the coast as the storm begins. In that case, you need moderate to heavy precipitation to dynamically cool the atmospheric column..or cold air advection (which usually comes after precipitation is over). They will both arrive at some point, during and after the storm respectively, but some precipitation could fall as rain..which ultimately will hold down amounts near the coast line. We included this in our forecast map.

We've got all the down-and-dirty details on the storm system below..including the processes that are driving it to occur in the first place! 



The details are still being ironed out by most of the forecast guidance, but the general idea is that a piece of the Polar Vortex will drop southward towards New England. At the same time, a piece of energy to the southwest of our area will move north and east, and eventually phase with the Polar Vortex in the Northwest Atlantic. The graphic to the left shows this development, as we can see the three stages of the phase in the middle of the atmosphere (at 500mb). We put a yellow dot over New York City as a point of reference.  In the first image on the far left, the southern stream energy over the Southeast states is moving north and east, which a broad piece of northern stream energy in relation to the Polar Vortex is moving east/southeast. We can see them begin to interact in the second frame (in the middle), and finally the phase occurs on the frame to the far right.

As the phase occurs, a strong surface low will develop over the Northwest Atlantic. At this point, some very heavy precipitation will develop near and to the north and west of the surface low. Fortunately for us, this will be after the system has passed our region. However, the forecast models are still showing a swath of light to moderate precipitation as the system passes by during the beginning stages of the phase.  We can see that in the image to the right, from the GFS model's depiction of the system. On the left side we can see the 6 hr precipitation valid Saturday afternoon, showing generally light to moderate precipitation over our area and heavier precipitation offshore. To the right, we can see the GFS forecast surface pressure...which shows the surface low well out over the Atlantic Ocean.

Finally, as the system phases, the Polar Vortex is pulled southward over New England later Saturday into Sunday. This will bring a shot of Polar Air to the entire area -- likely meaning one of the colder nights/days of the winter the second half of this weekend.