ALERT For Possible Hazardous Travel Early Wednesday then For Accumulating Snow Wednesday Night Into Thursday Morning

Frozen precipitation types will be possible at the onset of precipitation early Wednesday prior to a change into rain. Precipitation will then change into snow, from highest elevations down, beginning Wednesday afternoon into Wednesday night.

More limited wrap-around moisture, and a small change in air flow trajectories, has resulted in a reduction in forecast amounts through 17 December at all elevations.

Snowfall Forecast
(16-17 December 2020)

Generally 1″ or less below 3000 feet

1″ to 2″ at elevations above 3000 feet
(with locally higher amounts)

Target Snowfall: 1″ [(+/-) 1″ Error Potential] for Norton-Wise. This implies a dusting to 2″ of snowfall will be possible into 17 December 2020 across Wise and Dickenson counties. The greatest snowfall amounts, of 2″ or more, are expected at highest elevations in the High Knob Massif where rime ice is also expected.

Reference Early Winter 2020 for a brief recap of the recent event.

Miller B Type Winter Storm

An initial low that moves west of the Appalachians weakens as a secondary low begins forming along the Atlantic Coast. This second low may then impact the Northeastern USA, especially if the track is inside the 40 degrees N / 70 degrees W benchmark point, with heavy snow and wind (generally referred to as a Nor’easter).

While Miller B type Nor’easters can occasionally have a large impact locally with icing and heavy snow, (especially at upper elevations in the High Knob Massif), it is the Miller A type Nor’easters that tend to be crippling winter events for the local mountain region.

There are important aspects to be monitored, with these being climatological characteristics (all of which apply, at least partially, to each event of this type).

1). Evaporative cooling with dry air initially in place could support snow or a mixed period of frozen types at the beginning and front of the surface-reaching precipitation shield (early Wednesday).

2). The most significant snow and/or icing in far southwestern Virginia typically occurs at upper elevations in the High Knob Massif.

3). To the east, cold air wedging and upslope on easterly component low-level flow typically results in more prolonged frozen types across western North Carolina and the eastern portion of southwestern Va.

4). To the northeast, deeper cold air in the vertical typically supports more snow from the Greenbrier Valley of eastern West Virginia north and east along the West Virginia-Virginia border area.

5). Wrap-around and orographic upslope snow on the backside of the storm is typical, and sometimes can be very significant in favored upslope locations as temperatures drop with cold air advection.

For this event, wrap-around moisture is expected to be limited versus more productive events already documented in history.

Potential Christmas Winter Storm

The big news in the weather world, at least for those with hope for a white Christmas, is a signal for the potential (emphasis this far away on potential) development of a Christmas Holiday winter storm.

Although negative phases of the Arctic and North Atlantic oscillations are expected to continue (as they are currently negative), it is the formation of a positive Pacific North American oscillation phase that is a new trend that could aid deepening of a eastern USA upper wave (i.e., aid storm formation).

The persistence of blocking near Greenland and in the Ural Mountain region is an important aspect that is also working to generate atmospheric waves capable of impacting the Polar Vortex, which in the long-term (January-February) may influence future conditions across eastern North America.

Stay tuned for later updates.