The 12z GFS showing the low well south of the region, bringing only light snow to much of the area.

Colder Weather Returns…Light Snow Likely Friday

After a nice period of warm weather, a cold front came through this morning, allowing a Canadian airmass to build into the region.  Strong cold-air advection will cause temperatures drop through the 40s and into the 30s later this afternoon and evening. Windy conditions will continue with northwest winds 20mph to 30mph gusting to possibly near 45mph at times this afternoon. Temperatures will drop into the lower to middle 20s tonight, with northwest winds diminishing to 10mph to 20mph. Tomorrow will be mostly sunny with high pressure remaining in control. High temperatures will be in the middle to upper 30s — well below average for this time of year.

Model guidance is in agreement that a low developing over Southeast US will track well south and east of the region on Friday. This is because while the polar vortex will be lifting out Southeast Canada, the flow is too progressive to allow the upper-level trough to amplify enough for the storm to track closer to our region. Another disturbance rolling over the West Coast ridge, will keep this storm moving out into the Western Atlantic.

Clouds will increase by Thursday evening. Some periods of light snow will likely begin later Thursday night and continue into Friday morning via warm air advection ahead of the upper-level trough. This should accumulate on all surfaces, since we won’t have the March sun angle to deal with at night.

As the storm begins to intensify offshore, some more light to moderate bands of snow could develop for the coastal areas of New York City, Long Island and New Jersey, during the late morning and afternoon hours. Northeast winds may also increase to 20mph to 30mph with higher gusts near the coast during the afternoon hours with the tightening pressure gradient.

The 12z showing the low well south of region bring light snow to NYC metro region.

The 12z GFS showing the low well south of region bringing light snow to coastal areas of NYC, Long Island and New Jersey (PSU E-Wall). 

Currently we are anticipating only light snowfall accumulations — possibly 1″ to 3″ — most likely for coastal areas and on colder surfaces. Further inland, snow early in the morning is likely to taper to lighter snow showers or flurries, then end later in the day. Temperatures will be in upper 20s to lower 30s during the snow, which is cold enough for accumulations. However, with stronger March sun, the snow will have harder time accumulating on roadways and sidewalks during the daylight hours on Friday. We will need a pretty thick cloud deck, or heavier precipitation rates to get the snow to accumulate on the warmer paved surfaces.

There is the slight chance these accumulations go up. Despite the progressive pattern, the shortwave is still very potent, and with short wavelengths this time of year, it does not take as much amplification as usual to get a storm to turn northward. Northern stream energy does try to phase in an expand the precipitation shield northward, and if this continues to dive further southward, the flow could buckle a bit and allow the storm to come northward. A few GFS ensemble members show several inches of snow or more, and other global models have shifted NW. That being said, the models that are shifting NW are still SE of the GFS, and we are running out of time for major shifts. They might just be catching up to the GFS and then will stop shifting. We still feel the overall pattern is too progressive for a bigger snow event — there is only so much tugging northward that can occur in this setup. We will still be watching the guidance carefully this evening, however, for any trends.

This storm will move out to sea to Friday night. Any snow left over the area, will end by Friday evening. Seasonable temperatures and sunshine is expected for much of this weekend. Another disturbance passing by to our south may produce more clouds and snow showers Saturday night or Sunday morning. It is possible this disturbance stays far enough south, and we remain dry for the whole weekend.

This post was written and edited by Miguel Pierre and Doug Simonian