The Storm Prediction Center Has Issued A Marginal Risk For Possible Severe Thunderstorm Development On Saturday ( March 17 )
Storm Prediction Center Risk Regions For Saturday – March 17, 2018
Former Alerts
ALERT For Strong SW-W Winds Developing Tonight At Upper Elevations…Then Mixing Downward Across The Area During Thursday
Strong upper elevation SW-W winds will develop tonight, with blowing-drifting snow possible in open areas & along high crest lines. This could increase travel problems along State Route 619, State Route 706, Routes 238, 237, and State Route 160, to note a few, impacted by 6″ to 12″ of snowfall.
Strong SW-W winds will mix downward to middle elevation mountain ridges & exposed plateaus at some point between tonight and Thursday morning, then downward into lower terrain ( below 2000 feet ) during the day Thursday.
Wednesday Night Into Thursday Morning
Partly cloudy evening skies will give way to mostly cloudy conditions. Becoming windy. Blowing-drifting snow at the high elevations. SW-W winds increasing to 10-20 mph, with higher gusts, on mountain ridges-exposed plateaus below 2700 feet. WSW to W winds increasing to 20-30 mph, with higher gusts, on mountain ridges above 2700 feet. Temps dropping into the 10s and 20s, then rising through the 20s at upper elevations overnight into morning ( nearly steady or rising above 30 degrees on exposed middle elevation mountain ridges & plateaus ). Wind chills rising from the single digits below & above 0 degrees at highest elevations into the 10s toward morning. Wind chills in the 10s and 20s along middle elevation ridges-exposed plateaus.
Thursday Afternoon
Partly to mostly cloudy ( mid-level clouds ). Windy. SW-W winds 10-25 mph, with higher gusts. Temperatures varying from 30s to low 40s at upper elevations to the upper 40s to lower 50s ( milder in downslope locations with no snow ).
Thursday Night Into Friday Morning
Mostly cloudy. Small chance of rain showers or a mix of snow showers possible at mid-upper elevations. Winds shifting WNW-NW at 5 to 15 mph, with higher gusts. Temps varying from 20s at upper elevations to the low-middle 30s ( milder in downslope locations, especially to the south and southwest of High Knob Massif-Tennessee Valley Divide ).
Friday Afternoon
Mostly sunny. Some increase in high clouds. Light NW-N winds, except breezy to gusty along high mountain ridges. Temperatures varying from 30s to lower 40s at highest elevations over lingering snow cover to upper 40s to low 50s ( warmer south to southwest of the High Knob Massif and Tennessee Valley Divide ). Wind chills in the 20s to lower 30s at upper elevations.
The potential for another major winter storm is being monitored for next week. Stay tuned for later details.
Reference the above link for a review of one of the greatest winter storms ever documented in this region ( scroll down to the section about the then 20th Anniversary of this Monster Storm ).
Recap Of Snow Squalls ( March 13-14 )
Reference my 031118 Forecast for information on the complete storm event including forecast details.
To understand how this was an easy forecast to predict days in advance, consider the following:
The temperature in downtown Norton is 60 to 70 degrees, while at the same time the temperature in downtown Wise is 0 degrees. What would you think about that?
Now, invert that temperature difference into the vertical and you have the setting which developed late on March 13 into morning hours of March 14.
When orographic lift is applied, it becomes chaos with widespread significant snowfall. No places missed out in the upslope zone, even though amounts varied.
In downslope locations, such an extreme vertical temp profile acted to overcome the typical inverse forcing with orographics ( often called downsloping ) and generated localized streaks of heavy snow. Some to numerous places missed out.
High Knob Massif Webcam – University Of Virginia’s College At Wise
The most intense snow squalls of the 2017-18 winter season created widespread, significant accumulations across the mountain area with Winter Storm Warning criteria easily exceeded within upslope locations of Wise County.
High Knob Massif Webcam – University Of Virginia’s College At Wise
Snow squalls & local snowstreaks ( training squalls ) created whiteout conditions into morning hours of March 14, with new snowfall accumulations ( since sunset March 13 ) in the upslope zone varying from 2-3″ on the low end of the stick to 10″+ at upper elevations in the High Knob high country.
As little as 1″, by contrast, was reported in downslope sites such as in the Town of Big Stone Gap ( 1.4″ reported at the official recording site in the Tri-Cities ).
Snowfall & Snow Depth Reports ( March 13-14, 2018 )
Big Stone Gap 1.0″ ground depth
( Paxton Allgyer )
Clintwood 1 W NWS: 2.7″ 2-3″ ground
( Wayne Browning )
*City of Norton WP 6″-7″ ground depth
( Andrew Greear & Joe Carter )
*Parsons Gap – Wise 6.5″ ground depth
( Wally Smith )
*Depth included some old snow.
New Snow Depth At 9:52 AM – High Chaparral of High Knob Massif
Joe & Darlene Fields measured a total of 10.0″ of new snow in the High Chaparral community of the High Knob Massif, with 8″ accumulating between 7 PM March 13 and 9:52 AM March 14, followed by an additional 2″ by the conclusion of this portion of the event ( 12.5″ total during March 12-14 ).
High Chaparral of High Knob Massif At 9:53 AM on March 14, 2018
High Chaparral Community 10″ of total snow depth March 12-14: 12.5″ Total
( Joe & Darlene Fields )
GOES-16 Visible With Snowstreaks
Snowstreaks developed into March 14 to produce prolonged periods of whiteout conditions along trajectories in which they formed.
Although several people reported hearing thunder, amid or immediately prior to onset of very heavy snow, including myself, the closest lightning strikes detected were very near the Virginia-Kentucky border in Pike County, Ky.; however, that does not mean that they did not occur on this side of the state line.
Closest Lightning Strike Detected Over SE Pike County Prior To Local Thundersnow
While the lightning detection system is very good and likely picks up most strikes, a few likely escape in such settings with CSI and a slantwise cloud over mountainous terrain. There is no doubt that local snow was convective, with wind and intense snow so heavy that visibility was reduced to 100 meters or less amid climaxes.
Focus now shifts to an increasing pressure gradient as a frontal boundary approaches and stalls over the area, with wobbles back and forth to determine local temps as a rather significant NW-NE to SE-SW gradient develops across the boundary into this weekend.
