Monday, January 18, 2021

Mid-Winter 2021_High Knob Massif


18 January 2021
Eagle Knob of High Knob Massif
A Foot Or More Of Mean Snow Depth 
Cody Blankenbecler Image © All Rights Reserved

The deepest snow depths in the southern-central Appalachians have covered highest elevations in the High Knob Massif during the past couple of weeks, with 6" to 12"+ of snow depth that has 
now reached a foot or more in the mean.

A mean depth of 9" was measured at the City of Norton Water Plant (elevation 2365 feet) on the northern base at 9 AM on 18 January (part of a 18-day stretch with 3" or more of mean snow depth at Norton WP).

As of 18 January 2021, a total of 56.0" of snow 
had been recorded for Eagle Knob of the High Knob Massif (4196 feet elevation) during 
the 2020-21 winter season.

01 January 2021
Eagle Knob of High Knob Massif
Snow-Free Day For Depth Reference
Cody Blankenbecler Image © All Rights Reserved

While this is the deepest snow since the Christmas 2020 storm, when 10-18" accumulated, it has not occurred due to a single storm event but rather to many systems crossing the mountains.

This snow contains a base that is now more 
than 2 weeks old, such that it is becoming a 
true snowpack.

A snowpack is defined by multiple 
snow layers of varying age and density.

Appalachian Snow Cover
GOES-16 Visible Image

The central-northern mountains of West Virginia, the High Knob Massif, Beartown Peaks, and Mount Rogers-Whitetop areas in Virginia, and the highest summits along the Tennessee-North Carolina stateline (including the summit of Mount Mitchell) are the most favored sites for development of true winter snowpacks south of the Mason-Dixon line.

Only selected upper elevations in the Appalachians typically develop true winter snowpacks regularly, outside of the most severe winters, with short-lived snow cover more common across the bulk of this ancient mountain range.

The High Knob Massif, with its high basins, is the most consistent area in western Virginia for winter snowpack formation over the long-term (decades) as it stands highly exposed along the Appalachian structural front.


The majority of Virginia rests leeward of the eastern mountains of West Virginia, with only far southwestern Virginia being removed from these moisture extracting highlands on NW to N air flow trajectories. 

13 January 2021
Copernicus Landsat Image

Most of Kentucky, Virginia, North Carolina and even West Virginia (west of the mountains) have been devoid of snow cover recently (above example).

Another aspect to keep in mind, when viewing visible images, the snow depth can not be determined just by how "white" it appears on this type of image.  Burkes Garden, with 3" of depth on the above image, would appear to have more depth than the High Knob Massif (6"-12") because of the rolling to level and highly 
reflective nature of its basin floor.

The High Knob Massif forms a large bulge on the Cumberland Front, the southwestern extension of the Allegheny Front found farther northeast in West Virginia, that also marks the geological structural front of the Appalachians.


High Knob Massif
Precipitation Update

(Totals Listed By AM Measurement Format)
Monthly Total Precipitation
Big Cherry Lake Dam
(Elevation 3139 feet)

2019

January
6.14"

February
12.50"

Winter 2018-19
(1 Dec-29 Feb)
26.56"

March
5.93"

April
6.64"

May
6.75"

Spring 2019
(1 Mar-31 May)
19.32"

June
10.68"

July
10.77"

August
4.15"

Summer 2019
(1 Jun-31 Aug)
25.60"

September
0.63"

October
5.01"
( 5.89" to Midnight 31st )

November
5.20"
( 7.04" to Midnight 30th )

Autumn 2019
(1 Sep-31 Oct)
10.84"

December
8.52"

2019 Total: 82.92" (M)
 (January 1 to December 31 Period)

2020

*January
7.15"

**February
13.01"

Winter 2019-20
(1 Dec-29 Feb)
28.68"

March
9.55"
( 10.77" to Midnight 31st )

April
11.59"

May
8.73"
(6.90" on Eagle Knob of High Knob Massif)

Spring 2020
(1 Mar-31 May)
29.87"

June
7.48"

July
9.72"
(10.48" to Midnight 31st)

August
8.12"

Summer 2020
(1 Jun-31 Aug)
25.32"

September
6.21"

October 
7.06"

November 
1.96"
(Eagle Knob Snowfall: 0.5")

Autumn 2020
(1 Sep-31 Oct)
15.23"

December 
6.22"
(Eagle Knob Snowfall: 34.0")

2020 Total: 96.80" (M)
 (January 1 to December 31 Period)

2021

January 1-22
3.24"
(Eagle Knob Snowfall: 23.0")

November 2019-October 2020: 102.34"

Autumn 2018 to Summer 2019: 91.21"

Autumn 2019 to Summer 2020: 94.44"

(M): Some missing moisture in undercatch and frozen precipitation, with partial corrections applied for the 24.4 meter (80 feet) tall dam structure where rain gauges are located.  Corrections are based upon 86-months of direct comparisons between NWS and IFLOWS at Big Cherry Dam (including occasional snow core-water content data).

*General 7.00" to 8.00" at upper elevations (above 3000 feet) with 5.96" at the City of Norton Water Plant (official NWS rain gauge located at approximately 2342 feet elevation).

**Third consecutive February to reach double-digit precipitation totals within upper elevations of the 
High Knob Massif.

Near Big Stone Gap WP
South Fork Gorge of High Knob Massif
Wayne Browning Photograph © All Rights Reserved


Base To Summit Variations 
Precipitation During 2020

(Elevation 1962 feet)
Big Stone Gap Water Plant: 81.54"
Courtesy of Gary Hampton & Staff

(Elevation 2365 feet)
City of Norton Water Plant: 76.70"
Courtesy of Andrew Greear & Staff

Precipitation can vary significantly in complex terrain, such that the mean of 79.12" at 2164 feet (obtained by averaging the two base readings above) can only be taken as an estimate.

Big Cherry Lake of High Knob Massif
Wayne Browning Photograph © All Rights Reserved

Precipitation did increase to 96.80" at the 
elevation of Big Cherry Dam (3139 feet).

If this increase remained linear, it would 
mean that 116.46" fell at the summit level.

Summit Level of High Knob Massif
Wayne Browning Photograph © All Rights Reserved

Precipitation was likely not linear, although, it is very likely that well over 100.00" did fall on the high peaks during the January-December 
period of 2020.

Lake Basin Heads In High Knob Massif
Lidar Mapping of Upper Clinch-Powell Basins

Recall that 102.34" were observed at Big Cherry Dam during the November 2019 to October 2020 period (12-month water year).

A total of 99.10" were observed from 
Winter 2019-20 through Autumn 2020
(December 2019-November 2020).


Intense Snow Squalls
(17-18 January 2021)

Intense snow squalls beneath very cold air aloft generated 1" or more in just 15-minutes during the late evening of 17 January into the early overnight of 18 January (with hazardous road conditions).

Above intensity and duration was measured officially at Clintwood 1 W NWS Cooperative, however, an even more intense and somewhat longer-lived band of snow squalls impacted locations to the south and southeast.

An intense snow band of squalls impacted an area from the High Knob Massif, Norton-Wise, into the central and southern portion of Dickenson County with 1-2"+ of rapid accumulation.

Scroll through these images from the High Knob Massif Webcam at UVA-Wise to watch how intense these snow squalls became.  A Snow Squall Warning was not issued by the National Weather Service.  In fact, they were not even predicted by any office, officially, despite squalls having just occurred with a former upper-level cold 
pool some 24-hours earlier.

Images Courtesy of Computer Science-Mathematics Department at University Of Virginia's College At Wise



































































Minimum temperatures for the entire night-time period were generally reached during this intense band as cold air aloft was transported downward to the surface, with rapid drops in temperature (10s at highest elevations to mid 20s in lower terrain).

Up to 1" of snow accumulated to the floor of the Powell River Valley, with heaviest 2" to 4" amounts generally within the middle-upper elevations (above 2000 feet).

This was also not locally predicted by the forecast models, which have a bias (often erroneous) toward the Eastern Continental Divide and can overlook this initial orographic lifting zone (*).

*Following decades of research, a bias that should by 
now be very well known and adjusted for in forecasts.


Snow Cover & Southern Wave

20 January 2021
High Country Snow Cover & Local Snowpack

A limited extent of southern Appalachian snow cover was added to into early hours of 21 January 2021 as a wave moving through the sub-tropical 
jet stream interacted with cold air over area.

Nocturnal inversion formation in valleys aided sticking with cold temperatures (although rising temps occurred into morning), in addition to evaporative cooling amid initially dry air (a key factor in development of a period of moderate-heavy snow).

21 January 2021 at 5:26 AM
Eagle Knob of High Knob Massif
Cody Blankenbecler Image © All Rights Reserved

A mixture of snow and frozen types fell across 
the mountain area, with general 0.5" to 2.5" 
totals reported during the predawn through 
mid-morning period.

21 January 2021 at 5:26 AM
Snow Depth 10" (12" North Slopes)
Eagle Knob of High Knob Massif
Cody Blankenbecler Image © All Rights Reserved

Snow, fire, and bare ground were all on display from GOES-16 during afternoon hours of 23 January 2021.

23 January 2021
Southern-Central Appalachian Snow Cover


Rain-Snow Melt Event
(25-27 January 2021)

Significant rain and snow melt combined to bring steep creeks draining the High Knob Massif to near flood stage into early hours of 26 January 2021. 

Big Stony Creek Hydrograph
Roaring Creeks During 25-28 January 2021

No sooner had snow melted, more fell with a 
rapid moving system during 28 January 2021.

28 January 2021 at 2:00 PM
Wind Blown Snow on Eagle Knob
Cody Blankenbecler Image © All Rights Reserved

This was one of the most difficult snow events 
of the winter-to-date to determine actual snowfall, 
due to strong winds and blowing-drifting snow.

28 January 2021 at 4:30 PM
Wind Blown Burkes Garden Basin

A total of 8" were officially measured by NWS
Observer Pam Rose in Burkes Garden, where 
snow was highly wind blown (as seen above).

Burkes Garden was at the epi-center of the
heaviest snowfall associated with this event.

Snow-Free Reference Image
Burkes Garden Basin Floor

Snowfall totals varied from only 0.5" in lower elevations, such as reported by Mathematics Professor Chris Allgyer in Big Stone Gap, up 
to 4" to 8"+ in locations from the High Knob 
Massif to Burkes Garden.

29 January 2021
From The Mountains To The Sea
Copernicus Landsat Image

This system produced accumulating snow into 
the Coastal Plain of southern Virginia and eastern North Carolina.

28 January 2021
NW Flow Mountain Waves

While snowfall intensity was not as great as anticipated on the front end, snow showers continued longer on the back end to foreshadow the next event upcoming to begin February.


Miller B Winter Storm
(30 January to 03 February 2021) 

31 January 2021 at 1:31 AM
Eagle Knob of High Knob Massif
Heavy Snow And Blowing Snow
Cody Blankenbecler Image © All Rights Reserved

More than 2" accumulated with the initial band of snow during early evening hours of 30 January on Eagle Knob (0.7" at low elevations in Clintwood of Dickenson County) prior to overnight development of additional heavy snow (icing to the north in Clintwood).

Literal blizzard conditions developed in upper elevations of the High Knob Massif into the early overnight hours of 31 January.

This occurred as a Miller B Winter Storm began impacting the mountain region, with pressure gradient winds at 20-30 mph sustained and 
40-50 mph gusts.

31 January 2021 at 1:44 AM
Moderate Snow And Wind In Wise
Computer Science-Mathematics Department

31 January 2021 at 2:04 AM
Heavy Snow And Blowing Snow In Wise
Computer Science-Mathematics Department

Heavy snow continued through much of the overnight with Joe & Darlene Fields measuring 
6.5" of snow in the High Chaparral community.

Heavy snow extended across the high country to Big Cherry Lake and beyond, along the crest of Powell Mountain, to above the Duffield Valley along the Wise-Scott-Lee border.

31 January 2021 at 8:29 AM
High Chaparral Snow Depth
Darlene Fields Photograph © All Rights Reserved

Around 7.0" of new snow was estimated for the summit level, where 8" or more is on the ground (much more in places due to ROARING SW-WSW overnight winds as noted above) at mid-day.

31 January 2021 at 11:44 AM
Eagle Knob of High Knob Massif
Cody Blankenbecler Image © All Rights Reserved