Wednesday, February 20, 2013

SW Upslope Flow Snow of February 2013

Morning of February 19, 2013
High Chaparral of High Knob Massif
Overnight Wet Snow Accumulation
Photograph by Darlene Fields - © All Rights Reserved.

The High Knob Landform

Although not a classic event, roaring SSW-SW winds supported a period of heavy snow into morning hours of February 19 within the favored High Knob Landform - Tennessee Valley Divide corridor of the Cumberland Mountains of far southwestern Virginia ( Cumberland Overthrust Block ).

Elevation 3300 feet
New Snow from SW Upslope Event
Snow Depth of 4.5" In High Chaparral
Photograph by Darlene Fields - © All Rights Reserved.

I have documented many SW Upslope Flow snowfall events over the years, with a couple of classic events including those of November 1977 and March 1996.

The heaviest snow, in specific, fell across upper elevations of the High Knob Massif into adjacent portions of the Tennessee Valley Divide which were not in the downstream wake of the main crest zone of the massif during this February 19 event.

February 19, 2013
Large Snow Roller Shows Wetness of Fall
Photograph Courtesy of David Shelton & WCYB Archive

While SW winds can enhance rainfall in portions of the outward protruding Blue Ridge escarpment, such as near the Meadows of Dan, it is rare for there to be much snow.  Significant to major SW Upslope Flow snowfall enhancement is unique to the High Knob Massif area in Virginia ( specifically to those locations within and adjacent of its mass and amid its great calcareous landform ).

SW air flow trajectories rise more than 3000 vertical feet in their trek from Norris Lake to the summit level of the High Knob Massif ( southwestern North Carolina is another area where orographic forcing more rarely produces snow on SW winds, verses enhancements of rainfall which are prolific at that latitude & position ).

Morning of February 19, 2013
High Chaparral of High Knob Massif
In The Clouds Following SW Upslope Snow
Photograph by Darlene Fields - © All Rights Reserved.

New snowfall totals of 3" to 6" were widespread during this event in the High Knob Massif, above 3000 feet, with 1" to 2" ( locally up to 4" of depth ) at elevations between 2000 and 3000 feet not subjected to major downsloping leeward of the massif on S-SW winds.

It is stated as "new" snowfall since some old snow remained on northern slopes of the massif, in upper elevations, from the February 15-17 snow-rime event.

Winter Majesty of Mid-February Cold Blast

February 19, 2013
Rising Above The City of Norton
Pickem Mountain of High Knob Massif
Photograph by Roddy Addington - © All Rights Reserved.

Like the very tip of a great iceberg, majestic northern slopes of Pickem Mountain rise above the City of Norton to mark the front slope of a sprawling collection of ridges and valleys comprising the remnant high country mass of the High Knob Landform ( High Knob Massif ).

This was not a classic event for the Norton-Wise area since 925 MB wind trajectories at Lonesome Pine Airport in Wise averaged around 190 degrees ( 170 to 210 degrees ), which must cut across the High Knob Massif to generate downsloping. 

As later highlighted in the climatology section, it is not atypical for portions of the Tennessee Valley Divide resting leeward of the High Knob Massif to get snow shadowed, such as at Wise 3 E and Nora 4 SSE, with different events producing different results depending upon the precise wind trajectories.

February 19, 2013 at 6:22 AM
University of Virginia's College In Wise

Morning snow covered the ground lightly in the town of Wise, with snow melting away into the afternoon beneath impressive skies.

Februray 19, 2013 at 12:24 PM
University of Virginia's College In Wise

Roddy captured the morning coating in town.

February 19, 2013
A Coating of Morning Snow In Wise
Photograph by Roddy Addington - © All Rights Reserved.

At approximately the same elevation as Wise, but some 7 air miles to the southeast where air flow on this same 925 MB trajectory sinks much less getting into Jaybird Branch at the eastern end of the High Knob Massif, JoAnna Hobbs had significantly more snow at her home.

February 19, 2013
Far Eastern End of High Knob Massif
Snow On Jaybird Branch of Guest River
Photograph Courtesy of JoAnna Hobbs & WCYB Archive

Ideally, as shown by climatology, 925 MB air flow trajectories of around 230 degrees are preferred for heavy snow in Norton-Wise, coupled with 850 MB trajectories that are also SW-WSW.

Afternoon of February 19, 2013
Looking South from Lonesome Pine Airport
Panorama Looking Along High Knob Massif
Photograph by Roddy Addington - © All Rights Reserved.

SW air flows can stream up through Powell Valley and in between the Little Stone Mountain peak, on the far right, and the large mass of the main high country to the left, and reach Wise with minimal downslope on 230 to 240 degree trajectories.

SW Air Flow Thru The High Knob Landform
Preferred SW Air Flow Trajectory Into Wise
Photograph by Roddy Addington - © All Rights Reserved.

Due to channelization amid the High Knob Landform, and between the High Knob Massif and Black Mountain, SW air flow trajectories tend to produce the strongest winds of all directions into the Norton-Wise area.

Afternoon of February 19, 2013
Lonesome Pine Airport ( KLNP ) In Wise
Awesome Skies Above Strong Surface Winds
Photograph by Roddy Addington - © All Rights Reserved.

No signs of snow were left by afternoon hours of February 19 at Lonesome Pine Airport, with little snow sticking there ( less than 1" ) in comparison to other nearby locations at similar elevations.

Plot of 190 degree Air Flow Trajectory Path
Air Flow Came Across High Knob Massif To LNP

To illustrate how specific and important air flow trajectories are, a plot of the 190 degree trajectory path coming into Lonesome Pine Airport in Wise finds that it must travel across a large section of the High Knob Massif before reaching the Airport.

This is in contrast to places along the Tennessee Valley Divide located 7 to 9 air miles east of the Airport.

Plot of 190 degree Air Flow Trajectory Path
Air Flow From Clinch River Valley To Sandy Ridge

Wendy Carico reported 4" of morning snow depth at her home amid one of the highest sections of Sandy Ridge to the northeast of Coeburn, with an elevation about 100 to 200 feet higher than Lonesome Pine Airport in Wise.

This small elevation difference was clearly not the main driving force in snowfall differences observed between Lonesome Pine Airport and the Fairview to Banner Mountain section of Sandy Ridge.

Snowfall differences were driven by the pathway along which a mean 190 degree air flow trajectory had to travel in order to reach both sites along the Tennessee Valley Divide.

To reach the Town of Wise and Lonesome Pine Airport air flow had to first cross the High Knob Massif, with both moisture extraction and downsloping to its lee acting to hold back snowfall amounts.  By contrast, farther east, air flow was able to rise from the Clinch River Valley and bypass the massif into eastern-southern portions of Sandy Ridge ( northeast of the Town of Coeburn ).

During SW Upslope Snowfall events with deep air flow trajectories around 230 degrees ( 220 to 240 degrees ), the City of Norton and Wise Plateau can get more snow than portions of Sandy Ridge which then rests in the downstream wake of the High Knob Massif.

February 19, 2013
Looking Across The Orchard On Long Ridge
Photograph by Wayne Riner - © All Rights Reserved.

Just under 1" ( 0.7" ) of new snow fell on Long Ridge, at Nora 4 SSE, during this SW Upslope Flow event ( 3.6" fell during the February 15-17 period ).

February 19, 2013
Long Ridge of Tennessee Valley Divide
The Pond Nestled Amid Northern Slopes
Photograph by Wayne Riner - © All Rights Reserved.

Since Wayne & Genevie have been recording 
on Long Ridge it has been very interesting and instructive to observe how SW Upslope Flow snow events vary there depending upon incoming wind trajectories, with 900 to 850 MB layer winds appearing most critical to their temperatures and snowfall amounts during these events.

As I have written previously, one would not typically think about such a lofty mountain ridge setting as being under downslope flow ( as you would agree via the beautiful drive along Long Ridge ).

However, indeed, that is the case with very significant moisture variations there when air must first stream across the High Knob Massif ( as it does during many rain and some snow events ).

Morning of February 19, 2013
Snow Plastered Bird Houses On Long Ridge
Photograph by Wayne Riner - © All Rights Reserved.

Blowing snow was a notable factor during these recent February snow events along all of these lofty, exposed mid-upper elevation mountain ridges & plateaus, making both measuring snow and collecting it in rain gauges difficult!

February 2013
Blowing Snow On Long Ridge
Photograph by Wayne Riner - © All Rights Reserved.

SW Upslope Snow Climatology
High Knob Landform Corridor 
A Few Examples For Consideration

( 2006 to 2009 Period )
Mean 925 MB Wind Vector Composite
For Five SW Upslope Flow Snow Events

Looking at the most recent five SW Upslope Flow snowfall events, prior to this one, finds that strong SSW-WSW air flow dominated the 925-850 MB layer ( close to a layer mean SW trajectory ).

( 2006 to 2009 Period )
Mean 850 MB Wind Vector Composite
For Five SW Upslope Flow Snow Events

SW Upslope Flow snow events have historically been characterized as being "surprise" falls of snow, with 925 MB temperatures nearly always being forecasted to be above freezing in all but a few exceptions ( e.g., March 1996 and December 2008 ) associated with cold air advection episodes and anomalous warm advections ( e.g., November 1977 ).

The 925 MB level is typically around
the elevation of the Town of Wise.

( 2006 to 2009 Period )
Mean 925 MB Temperature Composite
For Five SW Upslope Flow Snow Events

Temperatures in the 900-850 MB layer are also typically forecasted to be near or above freezing, or to be rising above freezing over time with warm air advection ( a few notable exceptions below ) amid events not driven by gradients in cold advection.

A key feature in warm air advection regimes is that temperatures aloft not rise strongly above 0 Celsius 
( 32 F ) beyond the 825-800 MB level ( i.e., too much warm advection at higher levels will prevent the formation or change precipitation types ).

( 2006 to 2009 Period )
Mean 850 MB Temperature Composite
For Five SW Upslope Flow Snow Events

While cold air advection ( CAA ) on SW flow has occurred during these events, it is often a setting of warm air advection ( WAA ) into an air mass with at least initial evaporative cooling potential forecasted to be overwhelmed by WAA over time
( classic "surprise" snow setting ).

Since SW Upslope Flow snow events typically occur in either CAA or WAA regimes, examples below will be classified according to regime type.

Cold Air Advection Type
SW Upslope Flow Snowfall

Example 1 --- March 19-20, 1996

March 19, 1996 At 7:00 PM ( 00z March 20 )
850 MB Geopotential Height & Temperatures

A truly classic example of cold air advection and snowfall on orographically enhanced SW Upslope Flow occurred during March 1996, in association with a powerful synoptic-scale low pressure system.

A blizzard-like fall of heavy snow developed during afternoon hours of March 19 on strong SW winds from the Norton-Wise area southwestward, in contrast to only light snow showers and flurries in Pound and Clintwood ( on downsloping SW flow ).

March 19, 1996
ETA Model Initialization At 7:00 AM

March 19, 1996
Development of Blizzard On SW Winds
ETA Model Initialization At 7:00 PM

By 1700 hours ( 5 pm ) March 20, when low-level winds began veering NW, ground accumulations ranged from a mere 1" or less in deep valleys north of the High Knob Massif - Tennessee Valley Divide to more than 10" across upper elevations amid the High Knob Massif to Black Mountain corridor 
( with MUCH deeper drifts ).

Snow depths of 5" to 8" were measured in the Norton-Wise area, with wind blown drifts of 12" to 18" reported around Lonesome Pine Airport.  A huge contrast between Clintwood & Norton-Wise that highlighted the powerful upslope-downslope couplet.

March 1996
Virginia NCDC Climate Summary
Daily Snowfall For March 16-31, 1996
National Climatic Data Center - Page 23

Although a shift into NW Upslope Flow acted to complicate this event late on March 20 into March 21, with final snowfall totals reaching 18" to 25" in the High Knob Massif from High Chaparral across the main crest zone, the SW Upslope Flow period made it a great winter storm event.

Although snow depths decreased daily during this late season event, reports from early on March 21 revealed the significant contrast across the area.

By dawn of March 21 mean ground accumulations varied from 3"-5" around the communities of Pound, Clintwood, Birchleaf, and Breaks Village, 
to 9" in Big Stone Gap, 8"-12" in the town of Wise, 10"-14" in High Chaparral, and 12"-20" on Eagle Knob of the High Knob Massif where observer Dennis Salyer reported snow drifts of 5 to 6 feet in the gap between High Knob and Eagle Knob. 

Note that snow depths for Wise are officially recorded at 5 PM daily, with morning depths reported by Roy L. Wells, Jr., being greater than those on page 23 of the March 1996 NCDC report
( morning reports via personal communication with Roy ).

Example 2 -- December 1, 2008

December 1, 2008
Flatwoods of High Knob Massif
Heavy Wet Snow Falls Upon The Flatwoods
Public Photograph - WCYB-TV Archive

A more recent example of SW Upslope Flow snow with cold air advection developed at the start of December 2008, to mark the third SW Upslope Flow snowfall event of 2008.

November 30, 2008
NAM Model Initialization At 7:00 PM

December 1, 2008
NAM Model Initialization At 7:00 AM

Decmber 1, 2008
NAM Model Initialization At 7:00 PM

While no snow accumulated across northern Wise County, and most all of Dickenson County north of the Tennessee Valley Divide, it became deep across the High Knob Massif. 

By 8:45 a.m., December 1, Darlene Fields measured 4.5 inches of snow depth in the High Chaparral community of High Knob.  At around the same time, Wayne & Genevie Riner measured 2.2 inches on the Long Ridge of Sandy Ridge at Nora 4 SSE.  By contrast, nothing was on the ground in Clintwood, Pound, and Clinchco-Birchleaf with downslope flow.

Snow continued to fall with sticking and accumulation on a cooling upslope flow rising upward through the High Knob Landform and into adjacent portions of the Tennessee Valley Divide 
( i.e., Black Mountain, Wise Plateau, Sandy Ridge ) during the daylight hours.

Meanwhile, melting, non-sticking snow of a lighter nature ruled downslope locations to the north and northeast of the High Knob Massif with little to no accumulation during the afternoon in places such as the South Fork of Pound, Darwin, and McClure.

By 3 p.m., December 1, Darlene Fields measured 
7 to 8 inches of snow depth in her High Chaparral yard at 3300 feet above sea level.  At the same time, around 3 inches of depth was on the ground amid the Head of Powell Valley at the home of Elizabeth & Addison Stallard ( 1940 feet above sea level ).

A wind shift toward the west-northwest continued lighter snow showers and flurries into the early hours of December 2, with some accumulation in other locations.

Final Snowfall Totals
December 1-2, 2008

Clintwood 1 W:  0.7"

( FAA Radar Station )
Black Mountain, Ky.:  1.9"

Wise 3 E:  2.2"

Long Ridge of Sandy Ridge:  4.1"

City of Norton Water Plant:  4.9"

High Chaparral of High Knob Massif:  8.0"

Eagle Knob of High Knob Massif:  10.0"

The snowfall distribution by elevation 
within the High Knob Landform was:

< 1900 feet…less than 3 inches

1900 to 2700 feet….3 to 5 inches

3000 to 4223 feet….6 to 10 inches.

Locally less snow fell across portions of the Wise Plateau, where downsloping leeward of the High Knob high country became more of a factor ( During earlier events, on January 22 and February 29 of 2008, the Long Ridge section of Sandy Ridge also got caught within the downslope from the High Knob Massif.  In this case, the SW flow streamed across the lower eastern end of the massif and there was not as much downsloping into the Long Ridge area ).

Warm Air Advection Type
SW Upslope Flow Snowfall

Example 1 --- November 27, 1977

November 27, 1977 At 1200 UTC
850 MB Geopotential Height & Temperatures

A classic example of SW Upslope Flow snow with orographic enhancement, amid an atmosphere cold enough to support widespread snowfall, was observed during November 1977.

Snowfall developed with isentropic upglide of warmer air over an arctic dome, and became enhanced by orographic forcing as strong low-level southwesterly winds pushed into the High Knob Massif and adjacent high terrain along the Tennessee Valley Divide.

Public snow depth reports of up to 16" were received from Big Stone Gap, in lowlands of the Powell River Valley, with 11" to 14" depths reported from the Norton-Wise area northeast to Hazel Mountain along the Tennessee Valley Divide ( * ).

Although no reports are available for the High Knob Massif from this event, it is almost certain ( based upon many events since this time ) that snow depths were much deeper, especially above 3000 feet.

Snow Depths Reported In Virginia
Outside The SW Upslope Zone
November 27-28, 1977

Blacksburg 3 SE:  2"

Big Meadows:  2"

Monterey: 2"

Roanoke: 2"

Burkes Garden: 7"
( 12.5" of total snowfall )

Clintwood 1 W:  7"

Mountain Lake Biological Station:  7"
( 7.0" of total snowfall )

*An outstanding signature of this type of event is the difference in snow depths between Clintwood, on downsloping air flow with SW winds, and the Powell River Valley where 11" was reported in Pennington Gap and 16" in Big Stone Gap on SW winds upsloping through the High Knob Landform toward its remnant massif.

Example 2 -- January 22, 2008

January 22, 2008 at 10:00 AM
Heavy Snow Falling In Big Stone Gap
Sheila Durham Photograph - WCYB Archive

A typical forecast before WAA Events:

400 AM EST TUE JAN 22 2008


One problem prior to my climatic research on 
the High Knob Landform is that SW air flow trajectories were never fully recognized as being orographically enhanced flows with distinct upslope-downslope couplets in Virginia 
( i.e., like NW Upslope Flows ).

During CAA types when air is cold enough from bottom to top in the atmosphere to support snow, these SW Upslope Flow events result in distinct areas of enhanced snow amounts relative to what is forecasted and relative to locales outside of the main SW Upslope Flow zone.

Likewise, they result in areas of reduced snowfall
amounts via associated inverse forcing or downsloping.

During WAA types, when air may only be marginally cold and seemingly unsupportive of snow, SW Upslope Flow snowfall events result in unforecasted falls that often have fast hitting, high impacts upon travel.

A second, major problem is that SW Upslope Flow snowfall events occur less often than NW Flow events and are poorly handled by forecast models, especially those of the WAA type.

There are many cases of enhanced snow on SW Upslope Flow in the High Knob Massif area that may not be fully developed, or typical, such that snow accumulates to the floor of Powell Valley and the Powell River Valley.

When SW Upslope Flow of the WAA type becomes fully developed, accumulating snow levels reach the floors of Powell Valley and the Powell River Valley.

January 22, 2008
Warm Bullseye Over Heavy Snow Zone
NAM Forecasted Surface Temperature At 6 Hours

For example, during the January 22, 2008 event the NAM Model was forecasting a warm bullseye right over the SW Upslope Flow corridor that had the greatest low-level cooling.

In reality, moderate to heavy snow continued into much of the afternoon as adiabatic cooling on the upslope flow maintained a column of freezing air through the vertical depth of the precipitating atmosphere ( a nearly isothermal layer at lower elevations = BIG flakes ).

January 21, 2008
NAM Model Initialization At 7:00 PM

January 22, 2008
NAM Model Initialization At 7:00 AM

January 22, 2008
NAM Model Initialization At 7:00 AM

Snow depths of 3" to 4" were widespread from the floor of Powell Valley into the City of Norton and windward slopes of the High Knob Massif.

This event had a high impact upon the U.S. 23 and Alternate 58 corridors in Wise and Lee counties, as well as the extreme northern portion of Scott County.

The upslope-downslope couplet was active with only 0.5" of snow at Nora 4 SSE on Long Ridge and 1.5" in Wise which were again in the downslope wake of the High Knob Massif.

No snow to only a dusting occurred in downslope locations across much of the Russell Fork & Levisa Fork basins from Pound to Clintwood, Haysi, and Grundy.  In fact, this was mostly a non-event for the entire region outside of this favored SW Upslope zone.

Example 3 -- February 29, 2008

February 29, 2008
Heavy Snow Falling In Norton At 1600 Hours
Photograph Courtesy of Mr. Smith - WCYB Archive

NWS Forecast Discussion Before Event:

400 AM EST FRI FEB 29 2008



Forecast models prior to this event indicated that the vertical temperature profile would remain at or below freezing from around the 850-825 mb level on up through the atmosphere, such that at least some snow was expected to fall upon the highest mountain summits.

February 28, 2008
NAM Model Initialization At 7:00 PM

February 29, 2008
NAM Model Initialization At 7:00 AM

February 29, 2008
NAM Model Initialization At 7:00 PM

The morning began with a light coating of snow from passage of an overnight warm front, with 0.1" to 0.5" of accumulation being the general range from Clintwood and Wise south into the 
High Knob Massif.

An overnight minimum of 19 degrees at Clintwood 1 W climbed to 25 degrees by around sunrise, as the warm front passed with its light dusting.  

Increasingly gusty S-SSW winds were observed during the 0700-1200 hour period, in wake of the warm front.  A period of partial clearing allowed mid-morning sunshine and rapid temperature rises into lower-middle 40s across lower elevations of northern Wise and Dickenson counties 
( warming enhanced by downsloping winds ).

Temps struggled, by contrast, to reach mid-upper 30s in middle elevations ( 2000-3000 feet ) of the High Knob Landform - Tennessee Valley Divide corridor, from the Wise and Sandy Ridge plateaus southwest through the City of Norton into 
Lee County, on upsloping S-SW winds 
( colder at highest elevations ).

February 29, 2008
850 MB Vector Wind Composite Mean

Although James & Carol Bolling, who live on Little Mountain of the High Knob Massif just south of Big Cherry Dam, reported that the first snowflakes began falling by 1000 hours at their elevation of 3430 feet ( 4.0 air miles SW of High Knob peak ), 
it was early afternoon before any precipitation of significance spread across the area.

Snowfall became heavy across the upslope cooling zone by 1400-1500 hours, with low visibilities, as rain fell on downsloping into the Russell Fork and Levisa Fork basins from Pound to Grundy. 

Northern Scott County of High Knob Massif
Lorens Camp of Osborne Ridge At 5:00 PM
Photograph courtesy of Christy Lawson - WCYB Archive

The Bolling family measured 2.5" of snow on their truck by 1540 hours, with 6.5" drifts, as driving SW winds blew across the Big Cherry Basin.

Snowflakes were huge, indicative of a nearly isothermal temperature profile, with hazardous road conditions developing from Norton-Wise southwest into Powell Valley, Appalachia, Stonega, Keokee, and adjacent communities in Wise, Scott, Lee counties.

Numerous accidents were reported in the impact zone.  A white pickup truck rolled over onto its side to block a portion of U.S. 23 just outside of Wise, with several vehicles and a school bus sliding off State Route 706 of High Knob, between Tacoma and Robinson Knob, amid this "surprise" snow.

Darlene Fields, of High Chaparral, drove through the above conditions on Route 706.  She reported that small trees were drooped across the road by the heavy snow.

February 29, 2008
Heavy Snow On The Wise Plateau
Photograph courtesy of Summer Smith - WCYB Archive

This event exemplified what happens when SW Upslope Flow becomes fully developed amid a WAA regime, with 1" to 4" depths accumulating upon the floor of the Powell River Valley and Powell Valley in Lee and Wise counties.

New snow depths of 4" to 8"+ were common 
across the High Knob Massif during this event.

Total snow depths varied widely with old snow and drifting.  A general 1 to 4 feet of snow depth was on the ground across the main crest zone from Eagle Knob into Big Cherry Basin ( deepest on north slopes & drift zones ).

Once again portions of the Tennessee Valley Divide got into the wake of the massif during this event with snowfall totals reaching only 0.8" on Long Ridge of Sandy Ridge and 1.5" at the official measuring site in the town of Wise ( Wise 3 E ).

Most of the remainder of the Mountain Empire had rain with little to no snow outside of the highest elevations where 1" to 3" were reported in places like Burkes Garden, Banner Elk, Beech Mountain, Mount LeConte, and Mount Mitchell in the 3000-6000+ foot zone. 

Differences in measured water equivalent precipitation totals reveal the significance of the upslope-downslope couplet associated with SW flows in this area.

Water Equivalent Precipitation Totals
SW Flow Event of February 29, 2008

Downslope Locations In This Event

Blacksburg: 0.05"

Wytheville 1 S: 0.06"

Bland: 0.15"

Richlands: 0.23"

Clintwood 1 W: 0.30"

Burkes Garden: 0.32"

Lebanon: 0.31"

Grundy: 0.35"

Nora 4 SSE: 0.37"

Upslope Locations In This Event

Pennington Gap: 0.55"

Head of Powell Valley: 0.65"

Appalachia Lake WP: 0.67"

Big Stone Gap WP: 0.67"

City of Norton WP: 0.70"

Robinson Knob of High Knob Massif: 0.73"
( Robinson Knob IFLOWS: 0.56" )

Stickleyville of Wallen Creek Basin: 0.76"

*Big Cherry Dam of High Knob Massif: 0.76"

*From automated IFLOWS gauge.  Otis & Nancy Ward measured 0.73" in Robinson Knob verses the IFLOWS total of 0.56", suggesting the actual total was around 0.99" at Big Cherry Dam ( 23% more than IFLOWS ).

While SW Upslope Flow snow events are certainly a unique part of Virginia climatology, and can be simply wicked at times in the High Knob Massif, 
in particular, they only rarely attempt to rival the more potent and extreme TIM Circulatons already highlighted on this website.

High Impact Snowfall & TIM Circulation of February 2012

MEGA-Disaster of December 2009 & TIM Circulation

One rival to TIM events like those documented during January 1998 and December 2009, may have been the Great Thanksgiving Snowstorm of November 1950.

If old weather charts are correct, SW Upslope Flow would have played a prominent role in that massive snow event across the High Knob Landform.

This would have been a CAA type analogous to the March 1996 episode highlighted previously, but stronger and much more prolonged in nature with respect to its SW Upslope Flow snow.  Wow!

With respect to Powell Valley these phenomena, unique to Virginia, are polar opposites.  Like Dr. Jekyll and Mr. Hyde for snow lovers.  Powell Valley can not buy snow on a fully developed TIM Circulation, while it gets plastered on a fully developed SW Upslope Flow trajectory.  Amazing!

February 11, 2013
Mountain Waves Galore
A Golden Sunset From Long Ridge
Photograph by Wayne Riner - © All Rights Reserved.

Wayne Riner Photograph Thoughts...
"There were only the sounds of nature with the occasional bird making his final song of the day and wind was seen in the bare trees."

A simply AWESOME way to end this section!