Synopsis
A relatively fast moving offshore low is expected to bring this winter’s first round of accumulating snow in NYC. Fairly good agreement among different models suggests decent confidence of totals NYC in the range of 3-5″, and it is worth noting that trends have been towards a higher total in overnight model runs. In fact, both the Euro and GFS agree on about 5″ of snow for NYC by the end of this event, and I tend to agree with this end of the forecast range at this time.
Antecedent conditions with a shallow but decently cold air mass in place means the primary uncertainty arises from storm track. Subsequent model runs should help us determine if the storm will track on/near the 40ºN 70ºW benchmark, slightly inside (more snow), or to the east (less snow). The timing of the snow during the overnight hours into the early AM rush will help boost totals since we will have enough cold air in place. Moderate and potentially heavy snow is likely during a 3-4 hour window starting around 4 AM.
Forecast Details
At the Surface
Models are projecting a storm to develop off of Cape Hatteras and move close to the 40ºN 70ºW benchmark overnight, a position that historically signals the best snowmaking potential for NYC during coastal winter storms. This storm isn’t projected to be particularly strong, perhaps only dipping to 996-998 mb at its closest approach to the city, and it will be a relatively fast moving storm, both of which are factors that limit its potential to deliver large snowfall totals.
850 mb Level
There isn’t a strong sign of a robust 850 mb low-level jet with this storm. That’s in line with the profile of a weaker storm with less intense precipitation. However, most models are depicting strong 850 mb and 700 mb temperature advection and frontogenesis occurring for a few hours just south of the city, which could signal the possibility for some heavy snow bands to develop for a few hours overnight. It’s within these bands that we could see up to 1″ per hour snowfall rates, and as always, areas where these bands set up and persist the longest will ultimately pick up the higher end totals.
500 mb Level
Another supporting factor for a decent round of snow with this storm is that there will be a negatively tilted 500 mb through developing upstream of the surface low. This should aid the low in intensifying, though as stated above, it still won’t be a particularly potent one at the surface when it’s nearest to us.
300 mb Level
The 300 mb level shows a an exit region upstream of the surface cyclone preceding the event. The WPC does discuss a coupled jet scenario with the jet streak at this level eventually helping induce a lower-level jet which would boost snowfall totals, but the this might happen after the storm really impacts us.