We've been tracking this storm since last week... The first model to catch on to the final solution was the Euro (again), and the GFS eventually hitched a ride. The GFS win streak ends at 1 -- it usually does ;-)
I will try to break down my thoughts in order, and hopefully I answer all your questions...
1. When does it all start?
Good question ;-) -- So this has been something developing in the most recent model runs. It will be a good litmus test as to what range of snowfall accumulations we'll be heading for in the final round (I think anyway). So here's the high-res NAM on this:
NAM - 1am Tuesday
The initual rush of precipitation has now been coming up snowfall, as falling flakes cool the initially unsaturated air dynamically. Eventually, nearly all of this will wind up over to rain during the day Tuesday, but folks that are out on the roads early enough will catch this. Hunters may also be able to get a light coating on the ground before the changeover during the morning hours on Tuesday. Some of the models want to put up as much as 1" of snow with this, so it certainly can be something to watch early on. But, once we get into the day all this will be melted. If you wind up with the full amount, figure on the higher range of snowfall in the end (more on that when we get to it).
2. Okay, we did hear about the decent rains during the day Tuesday... So when do we change back to snow?
Let's first cover the rain itself. The NAM and GFS have both been getting wetter in the past few runs, with Charleston expecting over 1" of rain during the day Tuesday, and the Huntington area near 0.8". It's not the greatest kind of weather to be driving through to say the least.
Starting around 7pm Tuesday night, we should start seeing cold air both work forward from a stumbling front off to the west and also wrap-around the developing low pressure system on the eastern side of the Appalachians. As the low strengthens, so will the expanse of the wrap-around cold air. Rain changes to snow, and that change-over line spreads east of the next several hours to eventually capture our entire region by 1am on Wednesday. The first hours after the moment of change-over will represent the best prospects for steady snow. With that in mind, our western counties will have had most of what they're going to get by the time day breaks on Wednesday.
Travel weather is going to be pretty bad from Tuesday onward, particularly heading north, east, and south. Any route that intersects with the Appalachian mountains is a difficult one. Heading west is best (not that anyone has a choice in their travel destination). You'll still have to drive through some bad weather, but skies will be improving from west-to-east Wednesday.
3. I've heard about the threat for icing... When and where is this going to be?
As the moisture gets thicker during the morning on Tuesday, cold air will still be dammed up in the mountain valleys, unable to be scoured out by the over-running warm air. This sets up that icy threat.
The left-hand map shows the surface temperatures, largely above freezing south of I-64 and along the central sections of I-79. However, in the WV mountains and the WV/VA border, there are some places that will still be in the upper 20s. Aloft, at the 850mb level, the warmer air continues to advect in unimpeded, getting to +1 to +3 C by Tuesday morning. That level of warm air over-top sub-freezing temperatures at the surface is a good breeding ground for ice, as the falling rain will freeze on contact once entering that colder air right at the surface. It is expected that most locations eventually drift to plain rain before the change-over, so expect icing to only be bad right in the morning (when many are traveling). And "bad" is probably a relative term, as most will see less than a tenth of an inch. This has prompted Winter Weather Advisories for the mountain counties Tuesday morning, but as storms go this shouldn't be too bad.
4. When will it all end?
For many locations, the accumulating snows will wane right with the start of the morning.. About 9am in the River Cities area, then not until after lunch in the Charleston area. The lake-effect up-slope areas are going to continue in snow, and they can get more out of it because of that.
NAM - Wednesday Night
The ski slopes are going to love this. Snowshoe opens up this week, and then in early December the others will come online with this fresh snowpack.
5. So how much are we going to get?
I think that's what most folks are looking for, so now is a good place to talk about that. First, here are what the models are showing:
This is a pretty good amount of snow by November standards. In fact, when I first saw them, I went to researching, and here's something I saw:
In the last 50 years or so, here's the record one-day snowfall for selected cities:
Huntington: 4.4" -- 11/14/1969
Charleston: 6.0" -- 11/28/1995
Beckley: 6.3" -- 11/12/1968
Parkersburg: 5.3" -- 11/24/1971
Paintsville(KY): 5.0" -- 11/22/1989
Given these numbers, the models want to push this right up against the frontier of decades of experience. I'm not so sure I want to go that far myself. I don't like the rain-water ahead of the change-over, and in general my own model tweaking puts things slightly less than what these models are putting forth. Here's what I went with Monday morning for a first forecast:
Now, given the latest model runs as I type this out, I will say it is reasonable to look at adding another inch to these numbers. Anything more and we'd be challenging those multi-decade records. (Obviously none of this is near the Great Thanksgiving Storm of 1950 or the earlier November blizzard of 1938, but it would be the best since the 60s if we get the higher numbers). Perhaps it's my gut feeling and the disappointing previous two years that have me wavering. I did go more than the models in the first snow event this season-- So may be this storm can go a long way to establishing how the rest of the season will go relative to the model forecasts.
(As a final caveat, it should already be understood that the locally higher elevations and ridge-tops within these contours will get more snow than the folks around them. These contours can't account for all the rugged terrain. Feel free to adjust accordingly based on your experience in past storms and predictions).
I will put the tracking maps below. I will try to get to any questions when I can, but feel free to put in any comments and storm reports in the discussion section below as well. :-)
Have a great day everyone!