Friday, December 25, 2020

White Christmas 2020_High Knob Massif Area

1:04 PM on Christmas Day
Eagle Knob of High Knob Massif
Whiteout Conditions On Eagle Knob
     Cody Blankenbecler Image © All Rights Reserved

A foot or more of snow has fallen into Christmas Day along the windward slopes and crests of the High Knob Massif, from the base at the City of Norton Water Plant to the summit level (and snow was still falling).

An image from my friend Cody Blankenbecler, 
for comparison, showing lingering old snow on the 
Eagle Knob summit (4196 feet) prior to new snow 
helps to illustrate the huge increase in snow depth
(the 3:11 pm and 4:16 pm views being deeper).

12:06 PM on Christmas Eve Day
Eagle Knob of High Knob Massif
Lingering Old Snow In The Clouds
Cody Blankenbecler Image © All Rights Reserved

I was on Eagle Knob for the annual Christmas Bird Count and measured how much snow it would take 
to cover the bottom, solid frame of the door to this 
Virginia-Kentucky Communications facility.

It would take more than 5", which was achieved by 
the end of the main frontal snow band.  More total snow, however, appears to have fallen during this event since Midnight Christmas than fell during the frontal band.

Careful measurement, otherwise, indicates that 10" to 18" of snow depth is observed by flipping back-and-forth between the Christmas Eve comparison image and the observation images taken at 1:04 pm, 3:11 pm, and 4:16 pm (below) Christmas day (a period that featured snowfall rates of more than 1" per hour).

Much deeper snow drifts (several feet or more) will make travel hazardous to impossible along Route 237, Route 238, and State Route 619 until VDOT can plow the roads and this snow also settles (Route 237, and many others, are not typically worked by VDOT).

Joe Carter, veteran technician at the City of Norton Water Plant located at the base of High Knob, measured an average of 8" of snow on the ground at 9:00 AM Christmas morning (8.3" of total snowfall).

An additional 3.8" had fallen at the Norton Water Plant up to 2:30 PM Christmas, pushing the event snowfall total to 12.1" at approximately 2365 feet elevation.

Some specific details of this event.

City of Norton Water Plant
(8"-Diameter NWS Rain Gauge)

9:00 AM Christmas Eve Day
0.50" of rainfall (24-Hour Total)

5:00 PM Christmas Eve Day
0.69" of additional rainfall

Joe changed the rain gauge when a transition from rain to sleet occurred, helping to better document the total frozen precipitation.

9:00 AM Christmas Morning
1.52" (24-Hour Total)
2.02" (48-Hour Total)

Specific Breakdown:
1.19" rain / 0.83" sleet-snow

 A general 7" to 8" (7.5" average = 8") of snow was measured on the ground at 9:00 AM at Norton WP 
(1858 vertical feet lower than the High Knob peak).

A general 10" to 12" were on the ground at the 
2:30 PM observation at Norton WP, following nearly 4" of new snow since 9 AM.

9:00 AM on 26 December 2020
0.13" of snow water content
Mean Snow Depth: 9"
2.15" (Storm Total)

Specific Breakdown on Snowfall:
12.1" total (0.96" water content)
Max Snow Depth: 10-12" (11")

*An approximate 13:1 snow density, or 0.08" of water per 1" of snow, for the event is somewhat deceptive given that snow density began wet 
(8:1 to 10:1) and ended very dry (30:1).

*If using only the official NWS rain gauge catch (actual values would be somewhat different using snow cores as I did below at Clintwood 1 W).

High Knob High Country

23 December 2020
Along Route 238 on High Knob Peak
Lingering Snow Before The Christmas Storm
Wayne Browning Photograph © All Rights Reserved

Most of the old snow lingering from recent events melted, even on these upper north slopes, in rain prior to this heavy fall of Christmas snow.

23 December 2020
High Knob Peak of High Knob Massif
Lingering Packed Snow (Ice) on Route 238
Wayne Browning Photograph © All Rights Reserved

At this low sun angle time of year, and elevation, it typically requires a long time to melt away snow and ice (including on roads once it becomes packed), with Route 238 having been plowed and salted by VDOT in wake of the 17-18 December event.

Forest Service Route 237, along Big Cherry Basin, also had sections of packed snow-ice lingering on 23 December 2020.

23 December 2020
Looking Across High Knob Lake Basin
Wayne Browning Photograph © All Rights Reserved

It will now be interesting to see how long snow can 
linger in wake of this big Christmas Storm, given a 
stormy pattern upcoming by the New Year Holiday.

Above slopes, where I measure snow, had white Christmases during the following recent years:


This Christmas Storm of 2020 now marks the deepest snow since 2010, when 2 feet of new 
snow fell through the Holiday period.

Deep snow covered the high country in 2018, but 
it had melted and settled enough by Christmas to now be less than current snow depths in 2020.

Now, more about this current storm.

8:00 AM on Christmas Morning
High Chaparral of High Knob Massif
Darlene Fields Photograph © All Rights Reserved

Joe & Darlene Fields measured 9" of snow on the ground in the High Chaparral community at 8:00 AM Christmas morning (3300 feet elevation), during a 
brief lull in the action.

5:00 PM Christmas Day
Snow Depth In High Chaparral
Darlene Fields Photograph © All Rights Reserved

Factoring in settlement, the above ground depth by 
5 PM Christmas gave 12.5" of total snowfall for the High Chaparral community (nearly 1000 feet lower 
than the High Knob peak).

3:11 PM on Christmas Day
Eagle Knob of High Knob Massif
Cody Blankenbecler Image © All Rights Reserved

Snow fell heavily, amid squalls, at the summit level through the afternoon where the final total will have 
to wait until all snow ends (of course) and more data is collected.  Up until 5 PM, the preliminary storm total was in the 15-16" range.

A foot or more of snow (12.8") has also been reported near the crest of Black Mountain, along the Wise-Harlan border, as of 6:30 pm on Christmas evening.

Lower Terrain Toward The North
(Clintwood 1 W NWS)

Statistics for my official NWS station in Clintwood finds that 0.72" of rain had accumulated (versus 1.19" 
at Norton WP) when the transition to sleet occurred on Christmas Eve afternoon.

A total of 5.3" of snow accumulated with the main frontal snowband up through 11 PM Christmas Eve.  Ground snow depths varied from 5" to 6" .

An additional 3.1" of snow accumulated through Christmas day in off-on snow showers and squalls, with 6" of mean depth measured by sunset (the snow having settled due to low density and unfrozen ground beneath) and a storm total of 8.4" at 1566 feet elevation.

A settled depth of 7" remained on above ground objects and snowboards that had not been swept (6" to 7" on the ground = 6.5" which rounds to the nearest even whole inch or 6").

The rain gauge catch of 0.53" on the sleet-snow water content yielded a 16:1 snow to water ratio (0.06" of water per 1" of snow).  

Although light snow continues to fall (at 8:45 pm Christmas), I took a snow core and obtained 0.60" of water content to reveal a 12% rain gauge undercatch 
(in reality, because I sampled snow and little sleet in 
the core, the undercatch is a little more than 12%) 
at my highly sheltered, mountain hollow station.

The above also means that the snow density was closer to 14:1 during this event, beginning wet and ending dry.

[The final snowfall total reached 8.5" at Clintwood 1 W].

Extreme rain gauge undercatch occurs in snow at upper elevations in the High Knob Massif, and amid other high mountain sites, such that without highly shielded gauges the only option for more accurate representation of fall water content is taking cores of snow.

25 December 2020
Long Ridge of Sandy Ridge
Wayne Riner Photograph © All Rights Reserved

My friends Wayne & Genevie Riner measured a total of 7.9" of snow on Long Ridge of Sandy Ridge, with 5.0" accumulating during the snow band and 2.9" in snow squalls and snow showers through Christmas day.

Christmas Storm 2020
Final Snowfall Totals

(2650 feet)
Nora 4 SSE: 7.9"

(1566 feet)
Clintwood 1 W: 8.5"
(0.60" water content)

(2365 feet)
City of Norton WP: 12.1"
(0.96" water content)

(3300 feet)
High Chaparral: 12.5"

(4196 feet)
Eagle Knob: 16.5"
(10-18" mean depths)

Majestic Views From Above
(Southern Appalachian Snow Cover)

26 December 2020

Although clouds lingered to the northeast, majestic views of snow covering the southern Appalachians 
are highlighted by these Copernicus Landsat images.

26 December 2020

The structure of the great Cumberland 
Overthrust Block can be clearly seen!

26 December 2020
Without Any Labels
Southern Appalachian Fold-Thrust Belt

The 3125 square mile Cumberland Overthrust Block 
is the most visible geologic structure of its size in the southern Appalachian fold-thrust belt, with its broad, rootless anticline (Powell Valley Anticline of the 
High Knob Landform) and syncline forming the 
northwestern-most thrust sheet in the belt.

26 December 2020
Cumberland Overthrust Block
Southern Appalachian Fold-Thrust Belt

The geologic structure is polar opposite between the High Knob Massif (an anticline) and Black Mountain 
(a syncline).  It is also interesting that the existence of Black Mountain is very likely a product of crustal wave compensation generated by loading associated with the creation of the great Powell Valley Anticline.

In other words, it is no coincidence that the Middlesboro Syncline became vertically thickened northwest of what is today the High Knob Massif and adjoining terrain to the southwest where a partially overlapping duplex-imbricate system exists in the anticlinal structure.

Chilled Boundary Layer

4:16 PM on Christmas Day
Eagle Knob of High Knob Massif
Cody Blankenbecler Image © All Rights Reserved

Snow chills a layer of air near the Earth's surface.  This is largely due to incoming shortwave radiation by day that is used to sublimate or melt snow covered surfaces instead of heating them up.

Melting, evaporation, and sublimation are cooling processes for the atmosphere since they require energy 
input to drive them.  This varies from 80 calories per gram for melting up to about 680 calories per gram 
for sublimation.

Case in point, despite full sunshine on 26 December the 3:30 pm temperature was only 22 degrees at the City of Norton Water Plant and 26 degrees on the "sunny" side of the city.

Even in lower elevations, at 1566 feet, the afternoon max temp only reached 28.7 degrees at Clintwood 1 W.

The chilling capacity of snow is better known by night, when it enhances OLR (outgoing longwave radiation) and radiative flux divergence.  This is especially true with clear skies and light winds.  Enhancement occurs 
as decoupling develops in valleys and mountain basins.

This snow had potential for extreme temp minima, with air temps dropping to around 0 degrees or locally below in the High Knob Massif and on other high peaks, but the pressure gradient has been too tight for ideal conditions related to decoupling in valleys.

That is, prior to this evening (26 December) when 
there will be at least a window of time which may 
allow decoupling to occur in the favored valleys 
and upper elevation basins.

24-28 December 2020
Lower Elevations of Russell Fork Basin 

This period has felt so cold since relative humidity 
from a flux of sublimating and melting snow cover 
has kept the boundary layer moist (93% RH).

Big Changes In January

29 December 2020

Lovers of snow should not be depressed, despite 
mild start to the New Year, as major changes are 
likely to occur during January in association with 

Select 1080p HD for best viewing in Full Screen

Although produced from a UK (United Kingdom in western Europe) perspective, this video is excellent in its description of the Polar Vortex, its formation and break-down, and occasional major events known as Sudden Stratospheric Warmings (SSWs).

3 January 2021

Temperatures are warming dramatically above high latitudes in the stratosphere, and should reach near record magnitude as a major SSW occurs with 
a west to east wind reversal.

3 January 2021

Official Major SSW Declared
5 January 2021

As of 5 January 2021, an official major warming of the stratosphere has been declared with a simply incredible temperature increase and reversal of winds at 60 degrees North and 10 MB.

This occurred under influence 
of record strong Wave 1 forcing.

High-Elevation Snow
(3-6 January 2021)

4196 feet
12:13 PM on 4 January 2021
(View Following Some Melting)
Eagle Knob of High Knob Massif
  Cody Blankenbecler Image © All Rights Reserved

A light fall of snow, with 1-2" on the ground and approximately 1.5" of total snowfall, was observed 
at the summit level of the High Knob Massif during 
3 January into early hours of 4 January 2021.

4196 feet
12:48 PM on 6 January 2021
Eagle Knob of High Knob Massif
Cody Blankenbecler Image © All Rights Reserved

A general 2-5" of new snow fell at highest elevations 
within the High Knob Massif into 5 January 2021 to mark another elevation-biased event.

Riming continued in clouds throughout the daylight hours of 6 January, with air temperatures in the 20s at the summit level of the High Knob Massif.

Low Cloud Deck on 6 January 2021
GOES-16 Visible Image

Although there was not enough vertical temperature 
difference (lapse rate) over the Lakes to really activate their "snow machine," enough moisture was advected into the mountains to enhance precip amounts (and snow at highest elevations), with a general 0.50" to 0.60" at upper elevations 
in the High Knob Massif (versus 0.07" at TRI), and to help maintain a cloudy boundary layer capped by an inversion.

Persistent low clouds were a product of a Great Lake connected flow, which prevented clearing to the west (outside the moisture plume) from advecting into the southern Appalachians.


Saturday, November 28, 2020

Early Winter 2020_High Knob Massif

         Wayne Browning Photograph © All Rights Reserved

                        Black Lives Matter Statement

( Large section - Allow Time To Load )

A real wintry pattern is poised to take hold of the mountain region as December 2020, and Meteorological Winter, begins.

Moderate-Heavy Snowfall Potential

From a climatology perspective, this is the month that typically experiences a large upward increase in snowfall.

Analogous to an incline plane, snowfall amounts typically display a sharp increase from the foothills of southeastern Kentucky across the stateline as air is lifted along the Appalachian front range, above Clintwood and Wise, toward the High Knob Massif and Tennessee Valley Divide on WNW-N air flow trajectories.

Although many different air flow trajectories can comprise the snowfall for any given month, season, or even event, a significant portion naturally comes via air flow possessing westerly and northerly components.

Seasonal snowfall more than doubles from the 
top of the Kentucky foothills upward into the high plateau surrounding Wise, then doubles once again with continued lifting to the summit level of the High Knob Massif.

Enhancement of snowfall over the High Knob Massif 
is also due in part to the effect of mountain width, as discussed in research above, which acts to partially compensate for vertical height (or the lack of).

A summary of above research that is applicable 
to the High Knob Massif includes the following:

*Precipitation Efficiency increases with mountain width, with greatest increases occurring relative to narrow mountains like are typical in the Appalachians

*Mountain width acts to increase orographic robbing of moisture and to decrease the spillover or amount that survives in cross-barrier flow into leeward valleys

(Precipitation Efficiency = the ratio of total precipitation rate to the total condensation rate over a unit area)

A large decrease in snowfall typically occurs with forced descent and subsidence as air sinks leeward of the High Knob Massif and Tennessee Valley Divide into the Great Valley.

Although a very simplistic graphic can be used to illustrate what collected data reveals, the actual situation is far, far more complex than merely "upsloping" and "downsloping" of air as would 
be dictated by a terrain profile.

This leeward decrease being partly due to increased robbing associated with mountain width (discussed above) and the linked seeder-feeder mechanism (highlighted below) that often operates during cold season precipitation events.

While rime may be celebrated for its beauty, even without snowfall, rime also plays an important role in orographic enhancement of snowfall.  This occurs as falling flakes become rimed as part of a cold-season, seeder-feeder cloud precipitation process where by windward facing mountain slopes act to concentrate low-level moisture into terrain engulfing or scraping clouds (otherwise, called fog by those on the ground).

Orographic Seeder-Feeder Mechanism

The lack of resolution of this cold season orographic mechanism, which also possesses a well studied warm season form, is one reason forecast models struggle to accurately predict snowfall amounts across complex terrain of the Mountain Empire.

It is this process that negates the impact of sheer elevation.  In other words, while elevation is certainly important and can become the main factor in conditions where elevation dictates where snow can fall and stick, during many storm events the concentration of low-level moisture by windward slopes can generate more snow than would be predicted by sheer elevation alone.

The production and subsequent extraction of this moisture from air can also require that the air flowing downstream (air that has already dropped snow) be lifted into higher elevations (than otherwise predicted) along the secondary front of the mountains in order to equal the amount of snow generated by lower elevations with initial lifting along the primary front range (where air is initially lifted).

If air has limited moisture, secondary lifting is not sufficient to equal the amount of snow produced by lifting along the primary front of the mountain range.

The Cumberland Front, or southwestern extension of 
the Allegheny Front, denotes the southeastern edge 
of this initial lifting with respect to W-NW-N air flow trajectories (in this case, it becomes the primary front 
of the mountain range and the Blue Ridge become 
the secondary front).

Geologically, this southeastern edge also correlates to the Appalachian Structural Front upon which the folded and faulted sedimentary massif of High Knob forms a notable bulge (above).

Change air flow trajectories to E-SE-S and the Blue Ridge become the primary front of the Appalachians (where initial lifting occurs) and the Cumberland-Allegheny Front becomes the secondary front of the mountain range.

This explains in part why locations such as Boone 
and Banner Elk, despite being at significantly higher elevations, receive less snowfall (especially on W-NW flow) than Clintwood, Norton-Wise given westerly component flow is the most common within middle latitudes of North America.  The significance of this 
fact is unfortunately not well studied and recognized (and resolved) by models nor forecasters.

If inspecting the data in more detail, it is found that Boone and Banner Elk receive more snowfall than Clintwood and Norton-Wise on E-SE air flow trajectories.  This fact is well taught in meteorology classes and also well recognized by both forecast
models and forecasters.

This also explains in part how the High Knob Massif, despite being much lower in elevation above sea level than Mount LeConte and Mount Mitchell, can rival these highest summits with respect to longer-term, annual average snowfall.

Snowshoe Mountain, Canaan Mountain and Cabin Mountain in eastern-northern West Virginia (on the Allegheny Front) typically receive much more annual snowfall than the much higher summits of both Mount Mitchell and Mount LeConte thanks to added low-level moisture transport from the Great Lakes on W-NW flow.

Important Disclaimer: It should be noted that down-wind drift of snow on strong air flow is a major factor and hinderance to accurate measurement of snowfall within higher mountain terrain.  While this effect applies to all the high mountains listed above, it should in theory be greater at the highest elevations of Mount Mitchell and Mount LeConte (the Mount LeConte station likely being the best for more accurate representation of snowfall above 6000 feet in the Appalachians).

First Widespread Fall Of Snow

The first widespread snow of the 2020-21 season dropped a general 2" to 6" across the mountain area, with local variations from just over 1" to more than 6", especially along and north to northwest (N-NW) of the High Knob Massif and Tennessee Valley Divide (which includes Black Mountain on the Virginia-Kentucky stateline).

Eagle Knob of High Knob Massif

State Route 160 - Wise County (Black Mountain)

Snow Depth on Black Mountain (Wise County)

Long Ridge of Sandy Ridge

Looking Toward High Knob Massif
(2 December 2020)

Looking east from Black Mountain, VDOT snow plow driver John Varner captured a beautiful view of lingering clouds along the main high country of the High Knob Massif.

Little Stone Mountain joins the main high country mass at Little Stone Gap, the location of scenic Powell Valley Overlook, along U.S. 23 .

Breaks Interstate Park

2 December 2020
Dickenson County, Virginia
Russell Fork River of Big Sandy
Breaks Gorge In Breaks Interstate Park
   Wayne Browning Photograph © All Rights Reserved

An average of 2" was on the ground on north slopes of Breaks Interstate Park when I took these photographs of Breaks Gorge during afternoon hours of 2 December 2020.  A total of 3.5" was measured at Clintwood 1 W.

The Towers Formation of Breaks Gorge

Snowfall Event

(7 December 2020)

This snowfall event was elevation biased, with up to 2" of new snow at mid-upper elevations in the High Knob Massif and Tennessee Valley Divide (this fell on top of old snow at highest elevations).

A nice rime formation event also accompanied accumulating snow at upper elevations.

                                      Courtesy of WCYB-TV Chime In

Sunset (below) from the High Knob Peak.

Wayne & Genevie Riner measured 1.7" of snow at Nora 4 SSE, on Long Ridge along the Tennessee Valley Divide, in southern Dickenson County.

Snowfall (Non) Event

(14 December 2020)

Although up to 5" of snow fell at the summit level of 
the High Knob Massif, sticking was reduced (especially upon pavement and gravels) by mixing with rain.

This mixture occurred even though surface air temperatures remained below freezing.
How can that happen?

A thin layer of above freezing air just above the 
summit of the massif allowed falling snow to melt prior to reaching the ground, resulting in a rain-snow mixture during much of this event.

If the wave responsible for this had not been deamplifying (weakening) then the thermal advection would have been more significant and the transition more pronounced and impactful to better follow documented results of mean climatology of past systems featuring analogous surface low tracks and surface to 850 mb streamlines.

With surface temperature above freezing, lower-middle elevations (below 3000 feet) had only a minor impact from this system in terms of snowfall.

Foxy The Fox Squirrel
Wayne Riner Photograph © All Rights Reserved

14 December 2020
Long Ridge of Tennessee Valley Divide
Wayne Riner Photograph © All Rights Reserved

14 December 2020
Cow Paths Highlighted By Falling Snow
Wayne Riner Photograph © All Rights Reserved

Morning Views
(15 December 2020)

John Varner Photograph © All Rights Reserved

John Varner, of VDOT (Virginia Department Of Transportation), captured simply awesome morning views looking across a lingering layer of low clouds from the summit of Black Mountain, with crest lines 
of the High Knob Massif along the horizon.

                            John Varner Photograph © All Rights Reserved

I have labeled a few features for reference.

                             John Varner Photograph © All Rights Reserved

There was more total snow on top of the High Knob Massif than Black Mountain, even though it did not appear that way from GOES-16 and MODIS imagery.

Snowfall-Heavy Rime Event
(17-18 December 2020)

Snow has now covered highest elevations in the High Knob Massif during nearly the entire month of December, with conditions poised to turn more severe heading into the Christmas Holiday.

17 December 2020
Eagle Knob of High Knob Massif

18 December 2020
Forest Service Route 238
Courtesy of WCYB-TV Chime In

18 December 2020
Forest Service Route 238
Courtesy of WCYB-TV Chime In

State Route 160
Black Mountain - Wise County, Virginia

Virginia-Kentucky Stateline

Along State Route 160 - Black Mountain

Beautiful Morning Sunrise

A beautiful morning sunrise over the Tennessee Valley Divide, as captured by photographer Wayne Riner, contained an array of wave clouds.

19 December 2020
Long Ridge of Sandy Ridge

Mountain Waves

Glancing advection of Great Lake moisture into morning hours of 22 December generated nice mountain waves over the High Knob Massif.

22 December 2020
Southwestern Edge of Great Lake Moisture

Lingering Snow
Ahead Of Christmas Snowstorm

23 December 2020
Along Forest Service Route 238

Although the southern Appalachians had missed the major snowstorms up to this point, snow has covered highest elevations in the High Knob Massif nearly all month, and was lingering in advance of a significant Christmas Holiday snowfall event.

23 December 2020
Looking Across High Knob Lake Basin