122217 Forecast

Mountain Area Forecast ( Dec 22-25 )

My Forecast & Alerts With Later Verification Images Added

Upcoming And Current Alerts

 A Sharp Temperature Drop Is Expected Christmas Eve Night Into Christmas Day With Widespread Flurries & Snow Showers Tonight Into Christmas Morning As Air Temperatures & Wind Chills Turn Bitterly Cold.  

Light Accumulations Will Be Likely, With Most Significant Amounts At Upper Elevations.

The odds of having enough snow for an “official” white Christmas will be greatest at upper elevations in the High Knob Massif, and generally higher in locations along and upstream of the massif and Tennessee Valley Divide ( including communities such as Clintwood, Wise, Norton, Big Laurel, Banner Mountain, Herald, Carrie, Maple Grove, Big Ridge, Caney Ridge, Hill Ridge and Long Ridge as only a few examples of many ) versus locations lying downstream in river valleys of the Clinch, Powell, and Holston.

Snowfall Forecast ( Christmas Eve-Morning )

1″ or less below 2000 feet

1-2″ from 2000 to 3000 feet

2-3″ above 3000 feet

*Little to no snow accumulation is expected in downslope locations of the Clinch, Powell, and Holston river valleys.  Greatest amounts are expected above 3000 feet in the High Knob Massif.
High Knob Massif Webcam – University of Virginia’s College At Wise
Superintendent Andrew Greear, of the City of Norton Water Plant, reported 1.5″ of morning snowfall ( 1-2″ on the ground ) at the base of the High Knob Massif ( elevation 2342 feet ).
Darlene & Joe Fields reported 2″ of Christmas Morning snow depth in the High Chaparral community of the High Knob Massif.
Reference my 54-Year Christmas History below for a review of many past Christmases that possessed a similar distribution, with northern slopes within the high country of the High Knob Massif possessing one of the greatest probabilities ( 64% ) of having at least 0.5″-1″ of snow on the ground on Christmas Morning along the entire expanse of the central-southern Appalachians. 

Reference History Of Christmases Past

High Knob Lake Recreation Area – December 16, 2017

Former Alerts

ALERT For Strong SSW-SW Winds From Midnight To Noon Saturday For Middle To Upper Elevations And Lower Elevations In The Pound-Clintwood Corridor

A couple waves of moderate-heavy rain will begin to impact the mountain region Friday afternoon.  A low-level jet, with strong winds will develop between the heaviest periods of rain by late Friday Night into Saturday Morning.  Wind gusts of 30-50+ mph will become possible across middle-upper elevations.  The lower terrain has been added due to downward momentum transfer.

This verified well with a low-level jet developing along the western slopes of the Appalachians.

European Model 850 MB Analysis At 7:00 AM on December 23, 2017

Peak Reported Wind Gusts

49 MPH
*Lonesome Pine Airport

53 MPH
Black Mountain Mesonet

53 MPH
Flatwoods Mountain Mesonet

*Reported in between recorded AWOS observations.  Localized power outages were reported across the area.  No official NWS advisories were posted prior to this event.  This despite predicted formation of a SW flow jet ( not SE mountain wave jet ) along the western slopes of the southern Appalachians.  Emphasis on the strongest winds was placed on the wrong side of the mountain chain by forecasters, with a wind advisory being issued only following development of this high wind event ( speeds at the upper elevations would have justified a High Wind Warning ).  Numerous tree limbs, and some trees, were downed.
Miles of Road Debris In Wake of High Wind Event – High Knob Massif on Dec 24
Miles and miles of roads looked like the above following the high wind event of December 23.  Residents had to cut a few larger trees which completely blocked several roadways.
*Any forecaster who reads statements like above are wrong if they assume these are criticisms.  One of the biggest obstacles to forward progress and learning is such erroneous assumptions, as only with a mutual respect can forecasting in complex terrain be advanced ( respect between researchers and forecasters ).  For myself, personally, forecasting is only a by-product of my core interest which is the climate system and its components.  This website and the High Knob Landform were started as a means to document conditions in complex terrain that had previously been undocumented.  If advancement of forecasting through learning is a byproduct then it will be only one of many that arises from the undergraduate research program at the University Of Virginia’s College At Wise.
GFS Model 850 MB Wind Speed-Trajectory Forecast For 7 AM Dec 23, 2017

Strong Rises On Creeks And Ponding Of Water In Low-Lying, Poor-Drainage Locations Will Become Possible Into Saturday

A second wave of moderate-heavy rain, with possible thunder, will impact the mountain region Saturday.  Accumulative amounts on already wet ground will set the stage for strong rises on streams, especially those draining the High Knob Massif-Black Mountain corridor where rainfall amounts will be enhanced by orographic forcing on moderate-strong upslope flow during Saturday.

A general 1.50″ to 2.50″ of rain fell in Virginia-Kentucky border counties ( 2.15″ in Clintwood to 4 PM December 23 ), with locally higher amounts within the High Knob Massif-Black Mountain corridor.

Dropping Cloud Bases With Dense Fog Formation Will Be A Concern For Mid-Upper Elevations Along & North Of The High Knob Massif-Tennessee Valley Divide By Saturday Night Into Sunday Morning On Development Of Northerly Upslope Flow.  Freezing Fog Will Become Likely In Upper Elevations.

Rime From Freezing Fog In High Knob Massif – December 24, 2017
High elevations in the High Knob high country, into Christmas Eve morning, were rime coated but clouds remained so dense that it was impossible to get photographs to show the extent beyond close-ups.
In the above view Hawthorn ( Crataegus spp. ) trees, which here are Pleistocene relicts, are coated by an icy, glassy-type of rime which underwent deposition at temperatures in the 28-32 degree range.
A wet low-level atmosphere will combine with cold air transport on developing northerly upslope flow to drop cloud bases across middle elevations between 7 PM Saturday and 10 AM Sunday, in locations along and north of the High Knob high country and the Tennessee Valley Divide.  Very low visibilities will impact the busy U.S. 23 corridor between Powell Valley and Pound Gap within Wise County, as well as all mid-upper elevation roads and communities from extreme northern Scott County across Wise County into Dickenson County and southern portions of Buchanan County.
High Knob Massif Webcam – University Of Virginia’s College At Wise
Saturday evening ( December 23 ) cloud bases have been variable between 2500-3000 feet, and solid above 3000 feet, with sudden changes in visibility in the variable layer.  Temperatures are below freezing at highest elevations with freezing fog.  Drizzle has been falling at lower-middle elevations.
Lonesome Pine Airport – Prolonged Dense Fog
High Knob Massif Webcam – University Of Virginia’s College At Wise
Caution is advised for travelers along the U.S. 23 corridor and on all higher elevation roadways into Christmas Eve morning.


Detailed Forecast Dec 22-25

Overnight Into Friday Morning

Mostly cloudy.  S-SW winds 10-20 mph, with higher gusts, on middle-upper elevation mountain ridges-plateaus.  Low clouds ( dense fog ) at highest elevations High Knob Massif and Black Mountain.  Temperatures varying from 30s in the colder, sheltered valleys to the mid-upper 40s.  Wind chills in the 30s & 40s ( coldest in upper elevations ).

Friday Morning Through The Afternoon

Mostly cloudy.  A chance of drizzle or scattered light rain showers into early afternoon, then rain becoming likely.  Low clouds, dense fog at high elevations in the High Knob Massif early, then areas of fog developing with rain across the area.  Winds SSE-SW at 10-20 mph, with higher gusts, along mountain ridges-plateaus.  Temperatures varying from 40s in upper elevations to the low-mid 50s.  Wind chill factors in the 30s at highest elevations.

Friday Night Into Saturday Morning

Rain or Periods of Rain.  Heavy at times. Windy at upper elevations, then becoming windy at middle elevations by morning.  Winds S-SSW at 5-15 mph increasing to 15-35 mph, with higher gusts, at elevations below 3000 feet.  Winds SSW-SW 15-25 mph and increasing to 25-35 mph, with higher gusts, on mountain ridges above 3000 feet.  Temps steady or slowing rising in the upper 40s to middle 50s.  Wind chills in the 30s at highest elevations.

Saturday Afternoon

Showers. Thunder possible.  Rain may be heavy at times.  Windy.  SSW-WSW winds 10-25 mph, with higher gusts. Temperatures in the 50s to near 60 degrees, dropping during mid-late afternoon.

Saturday Night Into Sunday Morning

A chance of showers to drizzle.  Turning colder.  Dropping cloud bases with dense fog development possible at mid to upper elevations along and north of the High Knob Massif and Tennessee Valley Divide.  Winds shifting NNW-NNE and diminishing to generally 10 mph or less.  Temps dropping into the 30s, varying from upper 20s to around 30 degrees at highest elevations to mid-upper 30s.

Sunday Afternoon

Cloudy.  Colder.  A chance of snow showers & flurries, especially at upper elevations ( mix possible mid-lower elevations ).  W-WNW winds 5-15 mph, with higher gusts.  Temperatures in the 30s to lower 40s ( coldest at highest elevations ).  Wind chills dropping into 10s & 20s at high elevations.

Christmas Eve Into Christmas Morning

Snow & snow showers during the evening, then a chance of snow showers and flurries.  A snow burst possible during the predawn.  Turning bitterly cold.  Windy.  WNW to NW winds 10-20 mph, with higher gusts.  Temps dropping into the 10s to around 20 degrees, except single digits at highest elevations.  Winds chills falling into the single digits to low 10s, except 0 to -15 below zero across upper elevations above 3000 feet.  Rime formation in upper elevations.

Snowfall Forecast ( Christmas Eve-Morning )

1″ or less below 2000 feet

1-2″ from 2000 to 3000 feet

2-3″ above 3000 feet

*Little to no snow accumulation is expected in downslope locations of the Clinch, Powell, and Holston river valleys.  Greatest amounts are expected above 3000 feet in the High Knob Massif.

Christmas Afternoon

High clouds & cold.  WNW winds 5-15 mph, with some higher gusts.  Temperatures varying from 10s to lower 20s in upper elevations to the upper 20s to lower 30s.  Wind chills in the 10s and 20s, except single digits at highest elevations.

The potential for a significant winter storm is being monitored for late in Christmas Week toward New Year’s Weekend.  Stay tuned for later updates.


Weather Discussion ( Stormy Holiday )

Saturday Afternoon Update

High Knob Massif Webcam – Welcome To The Christmas Holiday
Sometimes this UVA-Wise webcam amazes even me, with sun rays showing lingering orographic clouds capping the massif along the horizon saying to all, Welcome To The Christmas Holiday!

To coin a phrase from a Rambo movie, of all things, the High Knob Massif will “draw First Blood” in terms of wonderland transformation into winter tonight into Sunday morning as riming and freezing fog engulf the high country.

The past 28 years shows that is actually more common than not there, but the problem for many lies in the drop of cloud bases to below the elevation of Wise to impact many folks traveling locally and along U.S. 23 ( a major north-south route ) between southern and northern states.  I posted this a couple days in advance, so hopefully it will benefit a few.

The good news, cloud bases will lift off middle elevation terrain by mid-morning Christmas Eve day as air flow trajectories change in advance of a upper air wave and arctic front that will bring snow showers and light accumulations Christmas Eve into Christmas Morn.


Early Friday Afternoon Update

High Knob Massif Webcam – University Of Virginia’s College At Wise

An orographic enhancement precipitation event is about ready to get underway, with long-lived, persistent clouds engulfing upper elevations of the High Knob Massif on a moderate SSW inflow.

*During my past 3 decades of research one of the most important signals of an orographic enhancement event has been the feeder cloud development in advance of a system ( as seen above ).
There are many important ingredients, with another being a moderate-strong inflow.  In this case a positive mountain torque will be generated as the atmosphere pushes against the terrain.
*With orographic enhancement events why does Doppler radar under-estimate precipitation amounts?  One reason is that the radar beam overshoots the orographic cap cloud environment which enriches the amount of precipitation ( rain and/or snow ) reaching the ground as it often falls out of higher altitude seeder clouds which the beam detects.  Precipitation at the surface is often heavier than the radar indicates as elements ( hydrometeors ) pass through the moisture rich cap clouds.
Why do rain gauges typically under report amounts?  A bulk of precip falling during orographic forcing events is wind driven, horizontally, generating often large rain gauge undercatches.  These strong winds likewise cause the rain, like snow, to “drift” such that surface amounts vary greatly over short distances ( as can be seen with snow ).  Rainfall drifts and is impacted by surface drag just like snow in the high country. 
As I have always stated, since I came to understand this aspect, the ultimate challenge is accurately recording and representing the true amount of precipitation which falls in a place like the High Knob Massif. 

There are a ton of weather changes upcoming between Friday and Christmas Morning, and I have tried to outline the major ones with headlines above the forecast.  Chances of a white Christmas remain low, with this being another example where just barely enough snow may fall for some places to officially have a white one ( but for most folks, it does not matter if it is “official” or not as long as some snowflakes are falling and sticking ).

I wish everyone a Happy Holiday & Many Blessings!


Previous Discussion

A stormy period of weather conditions is taking shape for later Friday through Christmas Eve, with a major transition from mild to bitterly cold air.

MODIS Terra Image For Thursday – December 21, 2017
A large variation in weather conditions was on display Thursday, with a notable upslope-downslope couplet across the High Knob Massif and Black Mountain area on S-SW winds.  Afternoon temps varied from around 40 degrees at summit levels of the High Knob Massif to lower 60s in the adjacent foothills of eastern Kentucky.
The high country of the High Knob Massif was engulfed in clouds throughout the day, with wind chills making conditions feel like 30s ( enhancing above noted differences with adjacent lowlands ).
High Knob Massif Webcam – University Of Virginia’s College At Wise

An orographic forcing setting is taking shape for later Friday through Saturday, with strong winds and wind driven rainfall ( especially at mid-upper elevations ).

NAM 12 KM Model Total Precipitation Forecast To 7 AM Sunday – Dec 24

Both the NAM and GFS are reasonably close in the position of the main rain band, and IF this positioning verifies then amounts within upper elevations of the High Knob Massif will be significantly higher than models are predicting due to moderate-strong orographic forcing and a pre-existing feeder cloud ( orographic pilatus ).

GFS Model Total Precipitation Forecast To 7 AM Sunday – December 24, 2017

The potential for strong rises on creeks, as well as for ponding of water in low-lying locations, will have to be respected if this setting verifies as predicted by current forecast model runs.

While antecedent conditions have been much drier than average since November 1, totals have been significantly greater than in the Tennessee Valley with 3.32″ at the City of Norton Water Plant and around 4.50″ on Eagle Knob of the High Knob Massif during the November 1-December 16 period.
NAM 3 KM Model Surface Wind Trajectory Forecast At 7 AM Sunday ( Dec 24 )

After the threat of significant rainfall wanes the first main concern will be a drop in cloud bases with cold air advection and development of northerly upslope flow by late Saturday Night into Sunday Morning.

This could impact travel along the U.S. 23 corridor across Wise County between the Powell Valley Overlook and Pound Gap.

The first chance for any snowflake action will begin early Sunday at highest elevations, with best chances for middle into lower elevations by late Christmas Eve day into the evening hours ( the period when sticking could occur ).  Amounts continue to look light.