The Low-down on a legitimate snow event

Snow is a-comin' ... Two questions that will be answered: How much are you going to get? Will it last through to Christmas?

Good Wednesday to one and all.

There's a reason why the Huntington / River Cities area has an average "White Christmas" percentage of 25% while the WV Mountains are upwards of 75%... This week will bear that out once again, making spirits bright for a lot of folks-- but not everybody.

First, let's talk about this approaching system. It's been on everyone's mind... ;-)

HPC - Wednesday Night HPC - Thursday Night

Our storm system first forms on the eastern edge of the Rockies, and intensifies as it moves into the Ohio Valley. On our Winter Weather Preview, this would qualify as an "Ohio Valley Soaker" event. However, and just as we said back then as well, it is the back end of the system where we'd be looking for snowfall. Indeed, the first-half is not going to go the way Santa wants it: gusty mild air pushing up from the south; temperatures making a run at the 60-degree mark. Once we turn the corner overnight Thursday into Friday, that's when the fun starts.

GFS - Thursday Night GFS - Friday Morning

As we've been talking about the past several blog posts, a good way to identify the regions where snowfall can enter the equation instead of a straight rain would be to locate those 850mb Temperatures on the maps. Here on the GFS, the temperature lines (called "isotherms") are the black lines. The solid ones are above freezing, while the dashed ones are below freezing, and the thick black one represents 32°F. Initially we'll be in the warm air (850 temperatures in the +6°C range), but by Friday morning the region will have cooled all the way down to the -8°C range. That's good enough for snowfall.

Next, we have to make sure there's good moisture in place while the temperatures are that cold. The good news here is that while our storm will be redeveloping closer to the coastline, the parent low pressure center will stall out over Lake Huron-- a prime place to be when trying to get snowflakes flying. For the Huntington / River-Cities area, windflow off of Lake Michigan is where the bulk of lake-effect snow comes from. Areas east of there (the WV Mountains) can benefit from both Lake Michigan and Lake Erie. I want to pull in the Euro model for this next set of images, looking at the staying power of the moisture. I do this to show the consistency among models, but also because the ECMWF has a nice 850mb level product.

ECMWF - 850mb Chart - Friday PM ECMWF - 850mb Chart - Saturday PM

Whereas a typical storm system has taller, thicker clouds such that a look at the 700mb level can get a good view of where everything is, lake-effect situations have lower cloud tops, so the 850mb level is a better gauge. Notice the deep plume of moisture still in place Friday evening, but it shifts to the northern parts of WV by Saturday evening. Friday evening also represents the last bits of influence from Lake Michigan as evidenced by the left-hand map. Whatever KY and OH want to get from this event, it will have to happen Friday.

Snowfall Forecast

I first want to get out what the models are talking about regarding snow from this particular system. Again, after the initial warm rain moves through, temperatures crash and snow flies by Friday morning, continuing into Friday night, but retreating to the eastern mountains beyond that.

Here's what the models are saying...

NAM - Snowfall Forecast GFS - Snowfall Forecast

(Click on either image for a larger one)

The NAM has a much better resolution of both terrain and data, but it only goes out a few days. This isn't a big deal for us though, because by Saturday most of the snow will have ended. The GFS goes out as far as we need, but it's grid resolution isn't as great. I think the GFS result is shifted too far westward as a product of this resolution issue-- If you realign it's bullseye of snowfall to where the NAM's is, you'd be on better footing. There is also clearly a larger contrast between mountain and valley on the NAM than the GFS. During these lake-effect snow events with strong pressure gradients, the NAM read-out looks a lot more like the final product.

Here's what my forecast is:

Brandon's Snowfall Forecast - Friday Through Saturday

Most of what the River Cities area, southern Ohio, and eastern Kentucky gets will happen Friday. We're looking mainly at a coating in the lowland/urban downtown areas, but can get as much as an inch or two more in any elevated areas (you know who you are). The same will be said heading into the Kanawha Valley. The Charleston area will see 1-3", but the residential ridgetops above the downtown area can score another inch or two above that. Also, those favored elevated areas in Putnam, Cabell, Lincoln, and Mason county can always get another inch or two above the average amount. As we get into the WV mountains, areas above 1500' will be in the 3-6" range, and be in line to see their snow continue into Saturday. This includes elevated locations along/east of I-79 and locations north of route 50. Places north and east of Beckley that are above 2000' now get into the 6-12" range, with the big numbers coming in the highest elevations in the Kumbrabow state forest, Snowshoe mountain slopes, and the Canaan Valley areas. Someone in there is going to be up around 16" or so. Keep following the updating maps below to see if your county ends up with a Winter Storm Warning or Winter Weather Advisory.

Be very careful on Friday, as both commutes will be impacted by the snow. Anyone heading up to the mountains might want to do so on Thursday, and then just stay off the roads through Saturday. Lake-effect snow is a volatile animal-- bands can form and drop a quick 1-2" of snow, and then vanish with breaking clouds, then come back again, etc.

Will it last..?

Now that's the $64,000 question.

Unfortunately, the next weather system to approach will be mainly a rain-maker... and it's coming on Christmas Eve.

GFS - Christmas Eve GFS - Christmas Morning

All parts of our area will be in the rain category :-( with the cold air locked up much farther north. The lowlands will see all of their snow melt before Christmas morning, and only the mountain lands (places that get more than 5" or so) will be able to hold onto enough snowpack to qualify with a 'White Christmas'. In those areas, get ready for that Thomas Kinkade wet, muddy, snowy "holiday gathering" imagery...

Well, maybe with slightly newer cars.

If any of you have any questions or comments, feel free to put them in the discussion section below. I would be happy to get to what I can :-)

Regional Radar/Satellite with Warnings Tracking

Accuweather Radar

From the Storm Prediction Center (below): Click For a Larger Image

Activity Overview Storm Outlook Watches Potential Watches Storm Reports
Temperatures HD Doppler Radar Estimated Rainfall Active Warnings
Current Temperatures HD Doppler Radar Estimated Rainfall Active NWS Warnings
Click For Larger Click For Interactive Radar Click For Larger Click For Larger

Have a great day everyone!



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