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.
Updated snow map, subject to change
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.
As you all have heard, confidence is increasing rapidly that the area will feel significant impacts from an early season winter storm. I will publish my first shot at a snowfall map but I encourage you to read the discussion as well which is where I explain the reasoning behind the snow map. This will be a little on the longer side just so you’re prepared. I have a timeline at the bottom should you want to skip to that part.
The Setup
We have a complex pattern out there right now that will have significant implications for snowfall on Wednesday. Lets start not on Wednesday, not on Tuesday, but night now.
10:00 AM observations from around the area.
Lets take a look at the current observations across the area right now. Notice all the 50’s with some 40’s and some 60’s? These temps have been here for a while (since last night) and are expected to continue through tomorrow morning. What we have with this type of setup is a very warm boundary layer (boundary layer is the layer of the atmosphere right next to the ground). This prolonged period of warm weather is thawing out the ground and causing both the ground, and the air right next to the ground, to be quite warm. Both of these factors will have significant implications down the road with potential snowfall.
With a wind off the water, ocean temps are another important factor that many overlook. At bouy 44007 (~25mi off the coast near Portland), the ocean temperature this morning was 50.3 degrees. Other bouys in the area confirm ocean temps right around 50 degrees. If the wind turns more easterly (even NE winds could be a problem especially in MA) then the warm air would be pushed onshore and the whole snow operation would be shut down.
Let’s look now to the upper air pattern and step forward in time. All images come from Accuweather with text/lines/shapes added by me.
0z CMC Model IDEA of 500mb pattern 7PM tonight.
Notice the two pieces of energy marked off on the map. They will round the base of the trough and form a storm off the Carolinas. The key to this forecast is the exact track of the storm and that will be determined by two pieces of energy diving down across the plains.
0z CMC Model IDEA on 500mb pattern 7PM Wednesday
They key to this forecast as I mentioned above will by the piece of energy pushing east across the Carolinas Wednesday. If this energy is faster, like the GFS, NAM, and CMC are saying, the storm tracks closer to the benchmark and a snowier solution ensues. Should this energy lag behind a little more, like the Euro says, the storm tracks farther west and a rainer solution ensues.
Right now I am leaning towards a compromise with a slight GFS bias due to the lack of blocking over the Atlantic. It is important to note that without strong high pressure in the western Atlantic, the door is open for the storm to slide a little farther east. This is the main reason why I favor the GFS solution over the Euro solution. However, with the Euro’s track record, it is very important to not discount it. A western track is still very possible.
The Action
Now that we’ve looked into the larger scale setup and some of the caveats to the forecast that only humans can pick up on, let’s get into what will really happen.
There are still differences between the models regarding the exact track and thus the westward progression of the rain/snow line. right now, I think it is safe to say that all coastal areas mix for at least some time. The greatest threat for mixing will be around 1 Am Thursday Morning and should come as sleet since the only nose of above freezing temps comes at 700mb. Everything above and below that is blow freezing.
There are a few things that are going in favor of coastal snow in this scenario. First off, this storm will be rapidly intensifying. The Euro has a pressure drop of 22mb in 24hours (7am Wed to 7AM Thu) so not quite an official ‘bomb’ but close enough (to be an official bomb, the pressure must drop 24mb in 24hrs). When storms intensify like this a few things happen. First, they tend to suck in cold air due to their rapidly expanding wind field. This could be a contributing factor in keeping coastal areas snowier for longer.
They also tend to manufacture their own cold air through a process known as dynamic cooling. This is a rather complicated process that can be boiled down to the cooling of the atmosphere in response to upward motion. We have a lot of upward motion associated with this storm due to its rapid intensification. This means that despite the fact that there will be little in the way of cold air at the onset of the storm, there will be a supply of cold air and that could potentially keep some coastal areas in the snow for longer.
Early thoughts on snow accumulations for the area. Subject to change.
I have opted to go conservative with the snowfall amounts especially at the coast to allow for the possibility of a westward track. I will continue to refine this and post revisions either here or on Twitter @Jacksillin.
Here is a timeline of how I expect things to unfold across the region. Highest impacts from heavy snow are expected to be felt Wednesday evening into Wednesday night.
Wednesday Morning: Snow approaches from the south, no travel impacts. Get travel and any storm prep done now.
Wednesday Afternoon: Snow overspreads the area and becomes heavy especially interior MA and CT. Snow changes to rain coastal SE MA. Travel impacts: Moderate
Wednesday Evening: Heavy snow moves into interior sections. Coastal areas south of Portland Maine inland to about 5 miles mix with sleet/rain. Midcoast Maine likely mixes as well. Travel impacts: High
Wednesday Night: Heavy snow continues especially interior NH/ME. Coastal Maine still stands the chance for mixing with greatest mixing potential still south of Portland. Rain/snow line starts collapsing in CT/SE MA. Travel impacts: High
Thursday Morning: Heavy snow moves into eastern Maine and snow starts to taper off. Mix line moves offshore of coastal Maine but still impacts SE MA. Snow ends CT/MA/NH. Travel impacts: Moderate, improving
Thursday Evening: Snow ends for everyone. Travel impacts: None
I will have more updates on Twitter this afternoon as well as all day tomorrow and throughout the storm itself. I’m @JackSillin. I will have a video out later today and will post the link to Twitter. I may or may not have another update on here tonight depending on how things play out. Next definite update will be tomorrow morning.
For the sake of timeliness (today’s forecast won’t be so helpful this afternoon when I’m done with the storm forecast), I will be posting two updates on the blog today. A full update on the storm and its impacts should be out in a few hours.
Radar image as of 7:45 AM
This morning’s radar shows widespread rain moving through the area this morning. The timing has shifted slightly, most of the activity is happening now as opposed to this afternoon but it’s wet morning out there nonetheless. Expect rain to be wrapping up midmorning but warm temps remain. Highs today will be in the 40’s north, 50’s south.
Tomorrow will be a warm and windy one with temps again in the 40’s and 50’s and a west wind. We have to wait until tomorrow night before high pressure builds in for temps to drop back down into the 20’s and 30’s. Sunnier skies should make a return as well when downsloping takes over in the afternoon.
I’ll have a full update on the storm including another video later on today.
Forecasterjack 