3/18 Late AM All Zones Update: Snowfall Threat Fizzles Out for This Weekend

Low pressure over the Great Lakes today transfers to another low developing off the Virginia coast, along a stalled frontal boundary with high pressure to the north by tonight. Some isentropic lift and moisture streaming off the Atlantic will cause more little more precipitation to develop by this afternoon, near this front. Especially over Northern NJ, NYC and Western Long Island. Areas further northeast and southwest, will likely see far less precipitation fall for the afternoon.

Thermal profiles suggest this will mostly snow over the Interior and a rain and snow mix over coastal areas. But most of the precipitation will be on the light side, with the lack of more upper-level forcing or dynamics. So with the March sun angle most roads will be wet, during the daylight hours. While some light coatings or dusting are possible on the grass or surfaces , especially over the Interior. Coastal areas will probably see very little or no snow accumulations.

An inverted trough with a low developing offshore that a few of our models showed some light or moderate snowfall for the region for tonight and Sunday morning, appears will stay weaker. This occurs shortwave energy around closed 500mb low digging into Mid-Atlantic is less consolidated with the low also remain more positive-tilt. This keeps more lift with PVA (positive vorticity advection) further offshore. Leaving the most of NYC metro region underneath of more NVA (negative vorticity advection) or mid-level subsidence later tonight into Sunday morning.

The NAM and to lesser extent the GFS models for the last few days, where in agreement in consolidating and phasing this shortwave energy closer to the region. As a result, the models were showing more lift enhancing banding with heavier snowfall rates and dynamic cooling developing especially over Long Island and Coastal CT.  But as discussed in our last zone forecast update, the ECMWF and RGEM models caught on to more disorganized vorticity around the 500mb low. Therefore they began trending drier for NYC metro and Long Island and Coastal CT over the last couple days, as well.

With those models taken in consider and initial warm boundary-layer temperatures our forecast was always for light snow accumulations, for the entire region. Surface temperatures will likely remain a little warmer with lighter precipitation overall for this event. So we are now expecting snowfall totals to wind up between a trace to perhaps an inch or two for most of the region, through tonight and early Sunday morning. Later tonight, after most precipitation ends, temperatures may fall to near or below freezing northwest of NYC. So any water on roadways could see some refreezing into black ice overnight.

More improving weather is likely on Sunday, as low pressure moves closer further away from the region. Skies should clear for more sunshine with drier northerly winds as the day progresses. Temperatures during the afternoon will reach the upper 30s to lower 40s over much the region with more sunshine expected. These temperatures are still below normal. Sunday night will be colder with temperatures getting down into 20s over much of the region.

But temperatures may begin moderating into mid-upper 40s  by Monday afternoon with rising mid-levels and downsloping northwest winds. Overall the pattern is expected remain progressive next week, with some light precipitation with few frontal system moving through and temperatures between below and above normal, every couple of days. Stay tuned for zone forecast updates through the weekend!