As of this morning’s update, the model guidance continued to have differences, especially with the GFS which only began to show widespread moderate snow affecting the area with its 6z run. The afternoon set of model runs came slightly closer to an agreement but with continuing differences with the exact handling of the phasing of the northern and southern streams, along with the timing and strength of the shortwave coming in behind the system which depending on its position relative to the coastal storm will determine how far west the heavy precipitation shield expands, along with the exact positioning and intensity of the heavy snow banding. The 12z ECMWF is the westernmost model, but with favorable dynamics extending northward of the low producing at least 8-12 inches of snow prior to any changeover to rain, while the CMC, NAM and UKMET support moderate to heavy snow across most of the area and the GFS remains the suppressed outlier. At this time, I am considering both the GFS and ECMWF as outlier models, and am currently siding towards a NAM/CMC/UKMET blend regarding an overall idea of the potential low pressure track and heavy snow axis.
Among some concerns to mention are a marginal cold air mass aloft; while heavy precipitation and strong dynamics are expected to keep precipitation type as snow under the heavy banding, this may result in heavy wet snow accumulations with snow to liquid ratios near or less than 10:1. Additionally, the positioning of the heavy snow banding is also to be considered regarding snow totals; in cases similar to this one, the model guidance tends to underestimate snow totals under the heaviest banding, while underestimating the sharp cutoff in snow totals inland of the banding. Based on the earlier noted scenario used for the current forecast, the heavier snow bands would set up over NJ into NYC, SE NY and southern CT. While there is not enough confidence to go into detail with specific accumulations, preliminary thinking would suggest a potential range of 6-14 inches of snow across the area, with the higher-end totals possible over northern NJ, SE NY and southern CT. As previously noted, uncertainty remains regarding the exact development system, however, and additional changes are possible over the next 1-2 days. More information will be posted with the next full update on Tuesday morning.