One or two

The biggest model disagreement has been whether the energy out west is split into two waves or stays consolidated in one wave. This largely has to do with how fast the energy in the SW US ejects east. The faster it is, the less tilt exists in the trough, allowing the northern and southern waves to phase. This senario would send surface low pressure close to New England with a band of heavy snow likely aligned across PA, N NJ, SE NY, and SNE.

The GFS has been trending in that direction since the 18z run yesterday which showed two distinct waves: The first passing through the confluence zone in the Mid Atlantic with significant overrunning precipitation, the second amplifying and moving just south of New England.


The latest 12z run has a much different senario than the 18z, with consolidated energy, and one stronger storm impacting New England. Verbatim, the 12z GFS delivers a one to two foot snowfall to much of the region.


The ECMWF has been back and forth with handling of the energy. The 00z 1/25 run had two distinct waves. The 12z 1/24 run had one wave, but still had some energy left back west. The most recent run, 12z 1/25 is fully phased. We are now in the Euro's hot range when it's hard to beat. So I think that the shift on the 12z could have been a full correction versus a trend towards a full correction.

The 12z UKMET also has one wave now. The NAM has yet to reach the same solution, but has been trending that way.

What it looks like at the moment:
Virginia, Maryland, into southern Pennsylvania and New Jersey should get some light to moderate overrunning snowfall during the day Tuesday.

Then the main event will be during the day Wednesday (old runs with the split energy had it on Thursday). The 12z model guidance suggests that this could be an intense storm system. We have a strong vorticity maximum ejecting from the southwest and tilting negative just east of the region. Per 12z guidance, there would be a swath of 8 to 16 inches across SNE and CNE. Coastal areas, cape, and islands will likely mix. Regardless of the exact details, this will be a high impact storm for much of the northeast with significant snow and ice accumulations.