UPSLOPE ROUND 1 WEDNESDAY-THURSDAY

December 9, 2025 8:41am

After a back to back central and southern Alleghenies winter events, the entire Allegheny region and especially the upslope region gets to join in on the action Wednesday in to Thursday. (Not only Wednesday-Thursday as there is more beyond)

A low pressure system passing north on Wednesday will have push moisture in across the Alleghenies. A southerly push of air with the associated warm front will stabilize temps 28-34 overnight and rise 32-36 Wednesday morning. As moisture moves in the entire column to the surface should rapidly cool to produce primarily all snow in spite of the “mildish” start relatively speaking. Surface temps remain steady through late day as the associated cold front swings through.

1- Expect snow morning through afternoon with temps steady upper 20s Wv tops, low 30s 2400-3000′. Initial daytime accumulation looks to be best above 2400′. Strong southerly winds in the morning shifting westerly midday. Gusting 35-50mph+

2- as the cold front crosses. A burst of snow, winds shifting W to NW and upslope snows increase. Snow ratios increase. . Winds gusting 40-55mph across the tops. Can we sustain a period to qualify as blizzard conditions. That is possible and its not out of the realm a blizzard warning could be issued across the higher Wv regions.

3- lingering but decreasing snow on Thursday.

My own thoughts on the event snow totals look like

The NWS and modeling is per similar

Lets run the Euro for this event:

The experimental RRFS model last year in these setups did pretty darn well with snow ratios. Snow Water Equivalent. It starts out 10 to 1. Many think thats a basic rule that 10″ of snow is 1″ of liquid. Across the high ground, and especially with upslope which makes up a good portion of the average annual snow. Ratios are generally much higher. In this case by Wednesday night in to Thursday a.m. 20 to 25 to 1 is likely common.

here is the RRFS Ratios. Showing is as I saw it perform well multiple times last year with this setup.

When the ratios increase, as does forecast error and needed snow range.

take this for example. Modeled hourly precip output. Say you are getting .05 to .1 in an hour at 20 to 1. There you picked up 1-2″ of snow. Say the model was off that little bit and no precip occured that hour. Totals may expect to be lowered from a simple .05 to .1 liquid. You dont think about that minimal liquid in a warm weather rain event. Say that .1 ends up being a lengthy squall and you get .2 in an hour at 15 to 20 to 1. There you got blasted with S+ 3-4″ of snow in an hour. Higher ratios greater the error. Now toss in 40-50mph winds with those higher ratios. It obviously blows it about and even in semi protected areas it takes out the fluff(air) of the higher ratio and depending where the observer is located and his measuring technique. Widely variable reports may be seen. Thus, snowfall reports historically are the least valuable data set.

And in this example of THE RRFS it ranges around 5″ for the Garrett County Airport. Example given how that can be fluxed up or down.

other model output:

6z Euro(personally I think some of these numbers get beat)

6z GFS

• Blended Model

as we go Friday through the weekend, 2 more events to watch

Friday

Sunday

Its very possible by next week this time a total week accumulation of 12-24″ across the high ground is possible.

This at times especially late weekend may be accompanied by below 0 air temps. So there are some extremes associated in here also. A very wintry week ahead.

NWS WATCHES

There is ABSOLUTELY NO reason eastern Preston shouldn’t be included in a upslope event. Aurora, Terra Alta, Cranesville all do very very well in upslope events. Even up along the Laurel Highlands and those may be added in today. Hello Pitt, State College.