It’s the Americans vs. the Europeans. Literally. The 12z model runs have offered a whole host of solutions ranging from no snow on the GFS/NAM to a snowstorm on the Euro! This is a big change from previous runs.
The key here is to get the STJ shortwave to phase with the polar jet to our south while the polar vortex north of Maine has to weaken and retrograde. If that doesn’t happen the phased storm will shear out ENE with confluence and shortwave ridging over SNE. The models seemed to point to this happening, but some of the GFS ensembles disagreed. Now, the 12z UKMet and the 12z
Euro have a big snow event for us and the 15z SREF mean does as well.
As I mentioned yesterday this setup is almost custom made for ensemble forecasting. Even though all the op runs showed a miss our potential was still there.
Take a look at the 12z UKMet for 00z Sunday. You can see the closed low north of Caribou has retrograded to the west and is being swallowed by the polar jet, all the while the digging (and phased) PJ is amplifying up toward our latitude. This allows the storm to hit us hard as the phases storm rides up the east coast and moves slowly thanks to upstream blocking. Confluence to our north provides cold air even down to the Mid Atlantic. A classic northeast (KU?) snow event.
Take a look, on the other hand, at the 12z GFS. The polar vortex north of Maine becomes stretched out and seems to even split. The somewhat phased STJ/PJ is forced to shear ENE out under SNE because of confluence and shortwave ridging north of NYC.
The issue here is what happens with that PV to the north and where exactly it goes? Does it split? Does it stall? Does it retrograde?
The 18z NAM and 15z SREFs have trended toward the snowier camp right now and I think that’s the way to go. The Euro/UKMet have been superior lately and they likely will be again.
Get ready… this could be a big one.