Snow Forecast for Saturday December 29, 2012

ISSUED: 12/29/12  5:34 AM

MORNING UPDATE: Made some slight adjustments with the location of banding and to take into account slightly higher dew points and thus warmer boundary layer along the immediate coast. In the light blue areas, snowfall accumulations of a trace to 2″ is expected due to some mixing of rain at times. This is an adjustment of one inch down. Also expanded this area through southwestern New Jersey due to temperatures near freezing already. The dark blue shade was adjusted to take into account where the strongest thermal gradient and thus mesoscale forcing will take place. The rest of the forecast is unchanged.

UPDATE: For the most part the forecast is unchanged for many locations. However, I did bump up totals just away from the coast to 3″ to 5″ (dark blue) because I’m becoming increasingly concerned with the threat for mesoscale lifting properties. There in lies the difference between models like the ECMWF (synoptic) and the more juiced up NAM/HRRR guidance. I think the NAM/HRRR are picking up the mesoscale lifting potential while the GFS/ECMWF are not. Note, all models have the same timing on the phasing, which is a bit earlier than thought this morning, and the same track. The difference is that the mesoscale models are picking up mesoscale features that the synoptic models have a difficult time doing.

Still, I think most people see around 2 to 3 inches of snow out of this low pressure system. A significant change in the forecast to snowfall totals like seen on the RPM would need a significantly faster 500 MB development that I think the RPM is overdoing, thus the forecast for a foot of snow in Connecticut. Is it possible? Yes, that’s possible for the whole region if the phase of the storm was much earlier and the low just exploded off the Delaware coast. Right now, I just don’t see any data to support such an outcome.

The following snow map is based on the latest guidance and observations.  Most locations will have 2 to 4 inches of snow, however there is a threat for a few mid level disturbances to enhance snowfall rates, especially over southeastern Pennsylvania, central New Jersey, and the New York City metropolitan area, which could push snowfall totals to 6 inches.  Along the immediate coast, there is a threat for a mixture of rain thus keeping accumulations down to the 1 to 3 inch range.  There is still potential for an earlier phase and thus a stronger storm, however at this time that is not expected.

SNOW MAP: (click on map for details!)

View Snow Map for December 29, 2012 in a larger map