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 ).
