Update - Snow and Rain Continue Monday

Storm arrives Sunday morning, but precipitation can linger on for days. Here's what you need to know...

Monday Update (9:00am) - Here's the snowfall accumulation map we went with for the morning shows today:

These are all in addition to what may have already fallen prior to the early morning hours today. Note how the rain contamination and the dry slot are working against snowfall totals in the traditional River Cities area, with more snow accumulating to the north, east, far south, and west. We don't call it the 'donut-hole' for nothing! :-)
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Monday Update (7:45am) - You can follow the full exposition of the forecast below, but this is an update tracking how things have developed since the overnight.

We're now into the waning hours of that 'dry slot' time period, and snow showers are gaining more ground across Kentucky and entering West Virginia from the west. Additionally, the mountain counties of the Mountain State have also been seeing snow (asifit ever quit there).

Here's the current surface map:

The dry slot wraps in-between the weakening parent low and the developing new system off the carolina coast. Today we'll go back and forth between rain and snow, with a weight toward snow in the early and later parts of the day, and then back to a preponderance of rain (in the River Cities area) during midday.

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Updates below (most recent 6:45pm)

Winter is the unwanted guest that continues to hang around on this Palm Sunday morning. Rain and snow (and some ice) approach, with a wide range of experiences in store depending on where you live. Here's the breakdown...

HPC - Surface Map - Sunday

A decent low pressure system moves across Kentucky and Tennessee today, toward the southern part of the Ohio Valley. Out ahead of it, rain, sleet, ice, and snow will overspread. I like to use the high resolution map products of the NAM in these situations to help pinpoint the timing of events, so we'll go through them by precipitation type, starting with the onset Sunday morning:

Sunday - Midday Sunday -  Afternoon Sunday - Night

Initially, those who get precipitation should primarily be seeing a cold rain. This makes it more likely that you can at least get in and out of Sunday morning church services with just the rain. However, dynamic cooling will occur as precipitation from above influences the air it falls through below. This will change rain over to wet snow, primarily north of the Ohio River-- places on a line from Portsmouth to Point Pleasant to Spencer. This can put down a coating of snow on the grassy surfaces, bridges and overpasses, but stay off the main roads. East of Charleston, WV, there is a concern for freezing rain/ice because of the chilly air that gets dammed in the elevated valleys. Be careful traveling starting Sunday afternoon on a line from Beckley up through Summersville and straight toward Elkins.

By late Sunday, the actual center of low pressure advances to our region, and the warm air advection that comes with the main circulation of the system will be sufficient to push the rain/snow line back farther north toward Jackson, OH and Parkersburg, WV eastward to Clarksburg along I-79. At this time, our anticipated secondary low pressure will spawn at the Carolina coast. This one will eventually take over and refocus most of the moisture out that way.

There are places that will stay all snow through this entire period, and those folks are on a line north of Jackson, OH to Parkersburg, WV eastward along Route 50, and then carving out mountains above 2000-2500' east of I-79.

NAM - Monday Morning NAM - Monday Midday NAM - Monday Afternoon

Monday morning's commute time looks to be a slick one for many parts of our area. Rain changing back to snow, or becoming snow for the first time in this event will start to accumulate. As the new low pressure system rapidly intensifies on the Atlantic coast, it will draw cold air into itself from the north and west dropping temperatures locally. Perhaps the place that will stave off the snow transition the longest will be the 'donut hole' river cities area that will have the benefit of a local maximum in temperature as the last bits of warm air wrap around the dwindling parent low. There will also be a "dry slot" working in as well-- a common feature of a double-barrel low system where one is filling in and the other strengthening. The original low will continue to fill in during the day, but retain a slight influence. This is why during the afternoon on Monday the models are trying to do the whole 'donut hole' thing again with rain as the precipitation type west of Charleston. This is going to be a gametime decision Monday in that area, as there are more influences toward snowfall than rain, but I can certainly see a right-on-the-line kind of event there. It just depends on how well our remnant low can, well, remain.

Beyond Monday afternoon we'll be looking at all snow at all areas, but the amount of moisture that remains will be sparing. We'll eventually shift over into a lake-effect controlled environment, so folks who live on the ridgetops and in the eastern WV mountains may well want to keep the shovel handy well into the coming week.

Examining the dynamics aloft, the GFS is usually the model of my preference for following the 700mb low (a good general target zone for the best snowfall in a large-scale cyclone or Nor'easter situation).

GFS - 700mb Chart (Heights/RH) - Sunday Evening GFS - 700mb Chart (Heights/RH) - Monday Morning GFS - 700mb Chart (Heights/RH) - Monday Afternoon

Judging from the above maps, any snow we'll see today will be highly susceptible to change-over, with the main influences being the warm air advection at the surface battling the dynamic cooling of the precipitation itself from above. By Monday morning however, we'll be in a 'sweet-spot' region for snowfall. We'll have to keep an eye on this for the morning drive. It's a fleeting thing though, because at exactly the same time, our new system is rapidly intensifying offshore such that only a few hours later the 700mb low jumps across the mountains and is now associated with the new system. Once that occurs, our snowfall here will transition to a heavy dependence on elevational lifting and lake-effect enhancement. This can often leave out the lowland valleys when it comes to accumulations.

So then... How much are you getting?

First I want to put up the model-based renderings and those of the National Weather Service. You can click on any of the maps below for a larger pop-out, and I definitely recommend doing so, because I'm making the initial images pretty small to save space. (this post is getting a little long)

NAM - Snowfall Forecast GFS - Snowfall Forecast NWS - Snowfall Forecast

The things all three forecasts agree on are (1) The donut-hole; (2) The deep snow forecast for the WV Mountains; (3) A decent snow on the northern side, just beyond where the rain/snow line makes its farthest push. The GFS is more juicy than the others, but I think it's also because it wants to add in some snowfall expected later into the week when it comes to the lake-effect.

Here's what I'm going with:

Thoughts: The hardest category (as usual) is with the lower snowfall amounts. It's quite possible that the River Cities area gets a couple quick coatings at different times during this storm, but nothing to show for it Monday afternoon. Various places on ridgetops can certainly see more than 2" if successive snow episodes stick. The most likely times for sticking snow will be Sunday afternoon and Monday morning (during the commute). As you get out of this region and into the higher snow totals, you will see widening snowfall times with less mixing/raining in between. Naturally the higher range snow will be on any localized high-points, with lower amounts on the valley floor. The ski slopes will love this snow (again), and we can anticipate some April skiing in the Mountain State. Don't forget, there is indeed an icing threat in the Beckley area on up paralleling the western side of the highest snow forecast contour. Be very careful traveling on local roads Sunday afternoon through Monday.

This is not the only snow we'll be looking at to finish off the month of April, as a lake-effect wind pattern takes hold from Monday night through Wednesday. But that is for another day.

I'll try to keep updates to this particular post, but it is getting quite long...maybe I'll start another one on it. For now, I'll put all the tracking map thingies together here at the end-- enjoy! :-)

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Update (6:45pm) - After a little lull in the action, our actual low pressure system finally approaches. It too has an associated dry slot, but that's not something we'll see until tomorrow. There's some thunder in there too with that line arriving. Most of it is rain, with some snow on the northern-most fringe.

Some early snowfall totals from viewers for the first pulse of this event (feel free to post yours in the comments):

Pocahontas County, WV: 5-6"
Vinton County, OH: 2-4"
Meigs County, OH: 1-2"
Athens County, OH: 1-3"
Scioto County, OH: Trace / Coating
Gallia County, OH: Trace / Coating
Mason County, WV: Trace / Coating
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Have a great day everyone!

-B

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