Doing another update this evening as 12z model guidance has come into better agreement and there are some relatively significant changes to the going forecast that need to be made as a result. On a different note, while it is very rare I post 3 times a day, I am planning on doing it again tomorrow as this is a high-impact storm and is occurring during the busiest travel day of the year. Wednesday will most likely also feature 3 updates. More frequent updates can be found by following me on Twitter @JackSillin.
The 12z models came into reasonable good agreement that the storm will track near or over the ‘benchmark’ of 40N, 70W. This places us here in Maine in an ideal position to receive heavy snow. While the Euro is still farther west than the rest of the models, it too came noticeably east and thus into better agreement with the GFS.
Confidence is increasing that this will be a mostly, or all snow event for areas in Maine. I have highlighted the areas I am concerned about regarding mixing below but mixing potential appears to have gone down quite a bit now that even the Euro, which is still the farthest west, fails to show temps above freezing at any level, for areas north of Portsmouth NH, even at the coast.
There are several factors at play here that could tip the balance either way, rain or snow. First lets look at the factors in favor of rain. First and foremost, this is November. The cold air that usually precedes large snow events is not in place at all. Remember, it’s 50 degrees out there now, temps have a long way to fall between now and Wednesday when snow starts to fall. Also, it’s important to note that winds will be from either the north or northeast, should the wind have more of an easterly component, the winds will be blasting the hot marine layer right onshore (water temps are running near 50 in the Gulf of Maine).
Now let’s look at the factors in favor of snow. First and foremost here, this is an intensifying storm. When storms intensify, a process known as dynamic cooling occurs on the NW side of the storm as upward motion results in cold air filtering down from the upper atmosphere to replace the warm air that is rising. When this occurs, the storm is ‘manufacturing’ its own cold air. With tremendous upward motion on the backside of this storm, it would not surprise me at all to see the rain snow line collapse southward in rapid fashion Wednesday night. In addition to the strong dynamic cooling expected to happen, cold air will be dragged in from Canada due to the rapidly expanding wind field and those two factors should be enough to keep most areas in the snow.
Although models have come into better agreement this afternoon, this is still a high volatility situation. There is still plenty of time for this to change.
I will have updates on Twitter this evening and will post here tomorrow morning.