My forecast verified well with respect to temps, wind, and relative humidity levels in the High Knob Massif, with the main problem being related to a rapid break up and dissipation of fog over the Norton Valley.
GOES-16 High Resolution Visible Image At 9:42 AM on October 6, 2018
A solid deck of fog is visible in Powell Valley and along the Clinch River Valley at 9:42 AM, just prior to the beginning of Hellbender 2018, with fog along the Powell River from near Norton through Appalachia.
Fog remained in Powell Valley and the Clinch River Valley at 10:02 AM ( below ), but was dissipating fast outside these locations. I had forecast a fog strip to extend from Powell Valley to just above Norton, along and above the Benges Rock section of the route.
GOES-16 High Resolution Visible Image At 10:02 AM on October 6, 2018
Dry air aloft, which helped high valleys drop well down into the 50s, also aided fog dissipation more quickly over the Norton Valley and a faster rise in temperatures between 8 AM and 10 AM.
High Knob Massif Webcam – University Of Virginia’s College At Wise
Beautiful skies greeted race time in the view looking south from UVA-Wise ( fog in Powell Valley, of course, not being visible from this perspective ).
GOES-16 High Resolution Visible At 3:02 PM on October 6, 2018
The mid-day temperature reached 72 degrees on High Knob, with 70-80% relative humidity, which was also the max for the day as persistent cumulus cloud formation helped hold temperatures down during the afternoon.
Hellbender 10K Race Forecast – 2018
This is a detailed look at the atmosphere during this year’s race, which is highly anomalous for High Knob or any mountain at this latitude in early October.
*Reference my Bottom Line and forecast below to omit this more technical discussion, which some will find interesting for the meteorology-terrain interactions.
The forecast sounding ( below ) at race time Saturday is one featuring a freezing level which is around 14,760 feet above mean sea level or, to put that into better perspective, if the tallest peak in the continental USA ( Mount Whitney ) were standing here the peak would still be just shy of the 0 C or 32 F degree Freezing Level. Simply amazing!
NAM 3 KM Model Forecast Sounding At 10:00 AM Saturday – October 6, 2018
Drier air is forecast to advect over the area aloft, as lower level air remains moist = a good chance for fog formation into Friday night-Saturday morning even though this high resolution NAM 3 KM Model is not forecasting a complete saturation near the surface, one of several adjustments which must be made to such models to more accurately depict weather conditions in the mountains.
Observe that the RH ( relative humidity ) in the 300-850 MB layer is forecast to be in the 35-40% range, over top of air that is 100% saturated near the surface ( in reality, not quite on the model ).
NAM 3 KM Model Forecast Sounding At 11:00 AM Saturday – October 6, 2018
A conditionally unstable atmosphere will be in place, which means it will be stable while unsaturated and unstable if it becomes saturated. The lower right inset shows Theta-E or Equivalent Potential Temperature, which decreases with increasing height to indicate that any layer becoming saturated will develop convective instability.
This is one reason that hit-miss showers and thunderstorms must remain in the forecast; although, with luck any local development will not occur until after the race is completed. The European and other models are forecasting a chance of localized development between 8:00 AM and 2:00 PM.
A low-level boundary layer inversion is expected to form into the overnight-Saturday morning with a combination of radiational cooling and drainage of cooling air downward from higher elevations in the High Knob Massif into the Norton Valley and adjacent Powell Valley.
Warmer air over cooler air is stable in the valley fog layer, but there will be a considerable amount of mixing near the top of this layer. Runners beginning in downtown Norton by 10:00 AM may be just beneath a fog layer, and depending upon how fast it can mix out could be running upward into a corridor of fog before climbing above the fogginess with increasing elevation.
NAM 3 KM Model Forecast Sounding At 12:00 ( NOON ) Saturday – October 6, 2018
Due to vertical mixing, the relative humidity along higher sections of the race course is not expected to drop below 70 or 80%; although, it should feel notably better than near saturated to saturated conditions at lower levels.
A transition from mountain to valley air flow will be aiding this vertical mixing process during the post-sunrise to mid-day period ( centered on mid-morning ).
Bottom Line, Forecast & Race Timeline
High Knob Massif Webcam – University Of Virginia’s College At Wise
The early evening prior to race day ( above ) features a notable layer of haze beneath clear skies ( drier air aloft ) which will be increasing overnight into Saturday morning to help generate formation of fog in valleys. Fog will attempt to grow in depth vertically into the predawn-early morning hours Saturday.
Vertically tall clouds above, and some localized showers, arising from within the moist boundary layer. Such will also be the case during this weekend.
An unseasonably mild and humid atmosphere will be in place for Hellbender 2018, with light winds. This is relative to what is more typical for early October.
There will be humidity changes vertically along the race course, with near saturation to saturation at lower levels versus less humid air with mixing at higher levels of the course ( but still humid for this time of year ).
Cooler air will be featured in the morning near the base with fog, or layers of fog, expected in between downtown Norton and the Flag Rock & Upper Norton Reservoir junctions with State Route 619.
Fog will mix out over time, and although the timing of this is unknown it is expected that air will be humid and close to saturation ( if not saturated ) in lower portions of the race course.
While valleys will be cooler than the summit level in the morning, this will reverse during mid-morning into mid-day Saturday as the low-level inversion mixes out and warms to unseasonable levels.
Higher sections of the race course are expected to feature notably drier air, versus saturation below, and more pleasant conditions into mid-day with temperatures in the 60s to around 70 degrees.
*An overnight update features the addition of possible fog formation at the summit level into morning with 4 AM RH values near 100%. If this occurs and does not mix out then higher sections of the course will have more humid air. Drier air aloft may still be able to keep it mixed out?
Friday Night Into Saturday Morning
Chance of a localized evening shower or thunderstorm, then becoming partly-mostly clear. Dense fog developing during the evening-overnight, especially in mountain valleys such as Powell Valley and the City of Norton ( and Clinch-Powell river valleys ). The fog layer may build vertically to include the Wise Plateau ( a possibility that has to be noted ).
Light S-SW winds, except 5-10 mph with some higher gusts on upper elevation mountain ridges. Temperatures varying from middle 50s to lower-middle 60s ( coolest high valleys ).
Saturday Morning Into The Afternoon
Partly to mostly cloudy with a chance of hit-miss showers and thunderstorms, especially during the afternoon. Winds S-SW at generally less than 10 mph. Temperatures varying from the upper 60s to the low-mid 70s ( coolest at highest elevations ) in the High Knob Massif, with upper 70s to lower 80s in surrounding lower-middle elevations.
Race Timeline
8:00 AM: 59 degrees in City of Norton with fog or low cloud bases ( or a fog layer just above downtown ).
Low-mid 50s in cooler high valleys of the High Knob Massif.
60 to 62 degrees at the summit level of High Knob with breezy S-SW winds. Chance of low clouds & dense fog.
10:00 AM: 63 degrees in Downtown Norton with a fog layer or breaking low cloud base above the city.
63 to 65 degrees at summit level of High Knob with partly cloudy skies as fog layer begins breaking on light to breezy S-SW winds.
A mixing layer in between downtown Norton and the summit level will be marked by fog that is beginning to break up and dissipate. Air flow along the massif will be undergoing transition (change) from nocturnal mountain (downslope) to daytime valley (upslope) air flow with increased vertical mixing.
This period can sometimes result in rapid vertical cloud development over the massif, and trigger showers, but with some luck localized shower or thunderstorm development will hold off until after the race is over ( however, this has to be noted and kept in mind ).
12:00 NOON: 76-78 degrees in Norton with partly cloudy skies. Light S-SW winds.
68 to 70 degrees at summit level of High Knob with partly cloudy skies ( vertically building clouds ). Light to breezy S-SW winds.
Unseasonably mild conditions will return to dominate the next 1-2 weeks, with another trend toward above average precipitation developing as well during this extended 5-10+ day range ( remember that October is climatologically the driest month of the year ).
The anomalous warmth of September is exemplified by a 68.5 degree average daily maximum on Eagle Knob of the High Knob Massif, which just beat the 68.4 degree average daily max observed during August!
How often are average September high temperatures warmer than August? A question to be researched, but a quick look through the Wise database from 1955 to 2012 reveals NONE. NADA. No year had a September with warmer mean highs than August!
Signs of a major pattern change are beginning to show up in the far extended range, by mid-late October into November as a late developing, central-Pacific based El Nino ( +ENSO ) continues to form and exerts more influence upon the synoptic-scale flow fields across the Northern Hemispere ( along with other factors ).
Overnight Into Monday Morning
Partly cloudy then increasing clouds toward morning. Areas of dense valley fog. Winds S-SW at 5-10 mph with higher gusts on mid-upper elevation mountain ridges. Temps varying from lower 50s to the low 60s ( coolest in mountain valleys at upper elevations ).
Monday Afternoon
Partly-mostly cloudy. Chance of hit-miss showers and thunderstorms. Light SSW to SW winds generally less than 10 mph. Temperatures varying from mid-upper 60s to the mid-upper 70s ( coolest in upper elevations ).
Monday Night Into Tuesday Morning
Mostly cloudy. Chance of a shower. SW-W winds 5-10 mph with some higher gusts on mid-upper elevation mountain ridges. Temperatures in the upper 50s to middle 60s. Areas of valley fog.
Tuesday Morning Through The Afternoon
Chance of showers & thunderstorms. SW-W winds 5-15 mph, with some higher gusts on mountain ridges. Temps varying from the 60s to the middle 70s ( coolest in upper elevations ).
Tuesday Night Into Wednesday Morning
Partly-mostly cloudy. Chance of a shower. Areas of dense fog. Winds WSW-WNW at 5-10 mph on mid-upper elevation mountain ridges. Temperatures varying from the middle 50s to the middle 60s.
Reference the High Knob Hellbender 10K section for a forecast specifically designed for this race in coming days ( my Cloudspitter 100 forecast will be featured during coming weeks in advance of this race ).
Weather Discussion ( More Of Same )
A brief cooling trend which came just in time for the 12th Annual High Knob Naturalist Rally will become a memory through coming days.
High Knob Lake Recreation Area – High Knob Naturalist Rally 2018
A buoy line can be seen across the lake in the far distance to keep kayaks and canoes safely away from the overflowing High Knob Lake Dam. Up to 3.50″ of rain were reported in the area immediately prior to the Naturalist Rally.
Temperatures in the 50s to lower 60s were observed during the time of this year’s High Knob Naturalist Rally ( 7:00 AM to 5:30 PM below ), with morning low clouds and fog slowly giving way to some welcomed afternoon sunshine.
Eagle Knob of High Knob Massif ( Time UTC )
Temperatures in the 50s during much of the rally were in rather dramatic contrast to 70s-lower 80s in the Tri-Cities, with some visitors seen shivering ( and talking about the chill ).
Beautiful Water Flowing Into High Knob Lake – 2018 Naturalist Rally
Mean averages during the next week to 10 days will be lower given decreasing sun angles, but nothing close to reality for this point in the year ( see graphics below ).
Approaching Sunset – Upper Norton Reservoir – September 29, 2018
While trees are changing again in spurts, the combination of atypical mildness + a lack of frost + anthracnose fungi impacts are making it slower and duller so far. The final result yet to be determined; however, clearly these ingredients are far from ideal and have already caused some significant leaf drop ( especially at the higher elevations above 3500 feet ).
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 1-5
A deepening western USA upper trough will turn flow more S-SW across the eastern USA over time, renewing the above average precipitation pattern.
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 6-10
While some signs of a major change are beginning to show up in the far extended range, the next 1-2 weeks are looking anomalously mild at this present time.
European 51-Member Ensemble Mean 850 MB Temp Anomalies: Days 1-5
Warm anomalies in the 6-10 day range ( below ) increase due to both a combination of deeper southerly flow from the tropics and to climatology, given temperatures should be declining ( in the mean ) moving through October.
European 51-Member Ensemble Mean 850 MB Temp Anomalies: Days 6-10
This could be setting the region up for a HUGE temperature crash once a change finally occurs, and this pattern flips from current upper air ridging into upper troughing.
An ALERT for redevelopment of low clouds and dense fog overnight through Saturday Morning.
Abundant low-level moisture will support dense fog formation, and low clouds, through the overnight into Saturday morning. Caution is advised for travelers.
Former ALERT
ALERT Continues For High Water Levels On Creeks Draining The High Knob Massif Into Friday Afternoon
As of 9:00 AM ( September 28 ) Big Stony Creek was dropping from an overnight crest of around flood stage, with a continuation of ROARING water levels.
Significant overflow had developed at Big Cherry Dam with ROARING water levels on South Fork of Powell River ( which remained below flood stage ).
Caution is advised along & downstream of these steep creeks for swift water and slick banks, this includes Little Stony Creek and numerous others along the Wise-Scott border area, through Friday.
Big Stony Creek of High Knob Massif
At 9:00 PM Thursday creeks were near flood stage, with around 3.00″ of total rainfall during this event at upper elevations in the High Knob Massif. Caution Is Advised in locations along and downstream of these roaring creeks.
High Knob Massif Webcam – University Of Virginia’s College At Wise
Wednesday Night Into Thursday Morning
Humid with a chance of rain showers. Thunder possible. Low cloud bases with areas of fog, dense at times, especially above 2500 to 3000 feet. Winds NW to NE at 5-10 mph, with some higher gusts. Temperatures dropping into the upper 50s to middle 60s.
Thursday Morning Through The Afternoon
Cloudy with periods of rain. Thunder also possible. Local downpours. Variable winds at generally less than 10 mph. Temperatures from around 60 degrees ( highest elevations ) to mid 60s to 70 degrees. Low cloud bases. Areas of fog, dense at upper elevations.
Thursday Night Into Friday Morning
Showers. A chance of thunder. Downpours possible, especially during the evening. Winds WNW-N at 5-15 mph, with higher gusts. Areas of fog, widespread and dense at upper elevations. Temperatures falling through the 50s, with 50-55 degrees at high elevations.
Friday Morning Through The Afternoon
A chance of drizzle or local showers. Partly-mostly cloudy. Winds NW to NE at mainly less than 10 mph. Temperatures varying from upper 50s to the upper 60s.
Friday Night Into Saturday Morning
Chance of drizzle, low clouds and fog redeveloping, dense and widespread fog above 2500-3000 feet. NW-N winds at generally less than 10 mph. Temperatures in the 50s, with upper 40s to low 50s in cooler mountain valleys.
Saturday Morning Through The Afternoon
Low clouds with areas of dense fog and possible drizzle through the morning. Rising cloud bases with breaks by mid-late afternoon. Light NNE-ENE winds. Temperatures in the mid-upper 50s to mid-upper 60s.
High Knob Naturalist Rally ( Sept 29 )
Looking Across High Knob Lake Basin – September 22, 2018
High Knob Naturalist Rally Forecast
Dense fog and low clouds over saturated ground is expected to be present through the morning, followed by rising cloud bases with breaks to partly cloudy skies during the afternoon.
Conditions will remain cool on light NNE-ENE winds. Temperatures will mainly be in the 50s at High Knob Lake ( be sure to dress for chilly conditions ) and may rise above 60 degrees if sunshine becomes abundant.
Friday – September 28 Temperatures at High Knob Lake
*University Of Virginia’s College At Wise Research Station National Weather Service calibrated temperature sensor ( Data Period: November 19, 2016 to Present )
*The average daily maximum during September 1-22 was nearly as warm as observed during July ( 73.7 degrees ), much above average for this time of year, and was warmer than the average summer maximum at High Knob Lake in 2018 ( 72.4 degrees ). The highest summer temperature reached 80.9 degrees ( 150 total minutes at or above 80 degrees during 2018 at High Knob Lake ).
A seemingly endless summer weather pattern is expected to continue through this week, and perhaps through the first week of October, per the latest trend of the European 51-member ensemble mean. The only exception being a brief period with notably cooler air this weekend, just in time for the Naturalist Rally!
Some of the coolest air will be Saturday into early Sunday as northerly upslope flow helps to bring a touch of autumn to the high country just in time for the Naturalist Rally.
Unfortunately, for those looking for true autumnal chill that will last it is just not in the cards. Not yet.
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 1-5
The only change in the short-term is a small drop in heights and minor weakening of the upper ridging before it builds back again.
The latest trend in the 6-10 day ( below ) is to maintain anomalous upper air ridging over the eastern USA to keep temperatures running well above average.
Note that significant chill at this time of year would be that which features mountain valley frost and freezes, especially in the high country. While air will cool some in upcoming days it will not be anything like typical for this time of year and may not be able to equal what has already been observed in August ( frost occurred during August 24 in Alder Swamp of Dolly Sods, Wv., where the lower dewpoint air was able to do its thing with drainage ).
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 6-10
This type of upper air pattern equates to much above average warmth for this time of year, with any cooler air in coming days being short-lived as a boundary stalls and lifts back northward once again.
European Model 850 MB Temperature Anomalies Forecast: Days 1-5
While most of Alaska has shifted back to unseasonable warmth ( above ), the bulk of Canada has turned chilly.
Significant changes are being noted in the 6-10 day range ( below ), with cold air building and pooling along the eastern side of the northern Rockies ( but with weaker anomalies than forecast a week ago ).
European Model 850 MB Temperature Anomalies Forecast: Days 6-10
This latest trend will shear away cold air building along the eastern side of the northern Rockies as it slides southeast into a rebounding upper air ridge.
Eventually, chilly air in Canada will be able to spread southeast but perhaps not until the second week of October? Stay tuned for updates.
Wetness Continues
High Knob Lake on September 22, 2018
*Cloud bases were engulfing highest ridges at the time this view was captured, with bases soon dropping to also engulf High Knob Lake Basin where every September day has featured RH-Dewpoints which have reached saturation. A trend observed during much of this growing season and likely responsible, at least in part, for Anthracnose fungal infections impacting many tree species at upper elevations ( especially maples and northern red oaks ).
Continued warmth will also support an above average rainfall trend, with showers & downpours in thunder-storms increasing in coverage. Again, the potential for locally heavy to excessive rainfall will need to be monitored through upcoming days.
Although heaviest rains with Florence remained to the east, September has been another wet month with 22 of the past 24 days featuring measurable rain in the official rain gauge at the City of Norton Water Plant.
This boosted 2018 precipitation to 55.59″ ( M ) with a general 59.00″ to 66.00″+ in upper elevations across the high country of the High Knob Massif.
( M ) = Missing moisture during February with a rain gauge spill.
Recap of Florence Rainfall Totals
A general 1.00″ to 3.00″ fell along the Cumberland Mountains, with much heavier amounts to the east and southeast ( as expected ).
Mount Mitchell SP: 14.32″
Meadows of Dan 5 SW: 7.99″
Whitetop Mountain: 7.08″
Boone NWS Cooperative: 6.22″
Grayson Highlands SP: 5.70″
NWS Precipitation Analysis During September 14-21
Although rainfall totals came in within or very close to the ranges on my forecast graphic they were held down somewhat by a more northerly turn of the low center, which tracked east of the official NHC track and model mean. This especially impacted the south-western portions of the mountain chain, where only 1.44″ were measured at Newfound Gap and 3.10″ on Mount LeConte ( atop the Great Smokies ). That was the big error on my graphic, with the 14.32″ not far away on Mitchell being on target ( illustrating how minor track changes can create a huge difference ).
Compare the NHC Official Forecast Track:
National Hurricane Center Official Forecast Track For Florence
To the Actual Inland Path followed by Florence:
Actual Florence Track Plotted On Google Earth
The Great Smokies and most of the High Knob Massif were to the left ( west ) of the track center. Heaviest rains fell mainly east of the track line. This created huge rainfall differences ( 11.22″ ) between Mitchell and Mount LeConte ( 14.32″ versus 3.10″ ).
*Weather stations on Mount Mitchell ( 6240 feet ) and Mount LeConte (6400 feet ) are only different by 160 vertical feet.
They are radically different; however, with respect to air flow trajectories and mean prevailing winds in terms of orographic forcing. The track difference with Florence illustrated this.
*A general 2″ to 4″ of rainfall is currently expected across much of the Cumberland Mountains. Greater totals will also be possible at upper elevations. Strong water levels rises will occur and flooding can not be ruled out should totals end up near, or above, the higher end of this forecast range.
Rainfall Totals During September 15-18 Period
*Flooding rainfall amounts are expected along and east of the Blue Ridge province, with widespread totals of 4″ to 10″ . Locally heavier amounts, with potential for up to 18″+ will be possible at higher elevations along the Blue Ridge ( e.g., Grandfather Mountain and Mount Mitchell ).
Lesser 1″ to 4″ rainfall amounts are expected across adjacent zones, with locally higher amounts possible at upper elevations in the Cumberland Mountains.
A chance of showers & thunderstorms Saturday will give way to increasing wind-rain into overnight hours of Saturday-Sunday as the remnants of Florence begin impacting the Mountain Empire.
Florence is currently beneath a weak wind field, but is expected to begin moving fasting in coming days. This motion will be critical to rain amounts as noted below.
Orographic forcing will be a factor with enhanced rain amounts on windward slopes-crests. The current forecast track will generate inflow changes over time, complicating the rainfall forecast over mountainous locations within the Mountain Empire.
*NOTE that eventual rain amounts will be dependent upon the speed of movement of these remnants, with slower movement generating heavier amounts than forecast and an acceleration resulting in lesser amounts than currently forecast.
Stay tuned to NOAA Weather Radio and your favorite media sources for updates on Watches and Warnings which will be issued during this evening.
The main concern for the mountains is how far inland will the remnants of Florence get + how fast will they move. The National Hurricane Center has been going with the European Model which has been, by far, the most consistent with the track.
Main jet stream cores are far to the north, and while there is some SW flow over the area now that is likely to weaken with large-scale subsidence in advance of Florence by later this week.
GOES-16 Water Vapor Image – Evening of September 10, 2018
While I think it will be Wednesday into Thursday before confidence on the inland track and speed increases by a significant amount, it is possible to discuss some of the possibilities ( for planning ).
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 1-5
The 51-Member European Ensemble Mean ( above ) shows Florence moving beneath a 500 MB upper air ridge axis during the next 5 days, which has been responsible for recent intensification.
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 4-8
The 4-8 day period, during September 14-18 above, keeps the main jet stream cores far to the north and a large, elongated upper ridge over the eastern USA.
The break or weakness in the ridge ( above ) shows where the remnants of Florence are likely to be.
Worst And Best Case Scenarios For The Cumberland Mountain Range
It appears nearly certain that Florence will turn into a disaster, perhaps a Mega-Disaster, for portions of the middle Atlantic. Historical odds would favor locations along and east of the Blue Ridge for worst conditions.
With the above noted, at this point in time, major flooding can not yet be ruled out for the Cumberland Mountains and surrounding Mountain Empire.
*While the European Model has been most consistent, individual runs and ensemble members have been widely varied on MAX rainfall amounts with up to 48.00″ ( 4 Feet ) in the worst case scenario being predicted for portions of Virginia and North Carolina along and east of the Blue Ridge. Anything remotely close to that would generate historic, deadly flooding ( of course, anyone knows that ).
Individual runs of the operational European, as well as its ensemble members, can be expected to continue to vary on rainfall amounts during the next couple of days despite a rather consistent trend of bringing a major hurricane into the Atlantic coast. A problem is with weak winds aloft the remnants will begin to slow down once it loses forward momentum and begins to feel frictional drag of the land.
Here I will briefly outline what would be the best and worst case scenarios for the Cumberland Mountains, where this website is mainly focused upon.
Best Case Scenario
The best case scenario to watch for would be that the remnants turn north following landfall and remain far to the east, keeping the Cumberland Mountains and Mountain Empire amid the subsidence zone of sinking air around the periphery of the core.
With a system like this one must begin to talk about orographic forcing, such that the best case setting for the Cumberland Mountains with the remnants moving far inland would be for them to move toward northern Georgia, southwestern North Carolina to maintain a southeasterly flow into southwestern Virginia and eastern Tennessee. This scenario, of course, would be the worst case for western North Carolina.
Worst Case Scenario
The worst case scenario to watch for would be for the remnant core to move toward northern North Carolina and southwestern Virginia, east of the Cumberlands, with a wrap-around northerly upslope flow generated into the local mountans with a stalling system. The orographics would then favor excessive rainfall over the local mountains and near the core of the remnant low ( especially on enhanced nocturnal convergence ).
There are many other possible scenarios, of course, but these are just ones mainly focused upon the Cumberland Mountains ( and based upon past climatology ).
