Mountain Area Forecast ( Sep 26-29 )

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.

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.

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 )

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

AM Minimum: 50 degrees
PM Maximum: 65 degrees

Previous Weeks In September:

High Knob Lake

*September 1-22, 2018
Elevation 1074 Meters ( 3523 feet )

Average Daily Maximum: 73.2 degrees
Average Daily Minimum: 61.1 degrees
MEAN: 67.2 degrees
Highest Temperature: 78 degrees
Lowest Temperature: 59 degrees

*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.

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 ).

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.

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 ).

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

*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.

City of Norton WP
( September 1-24 )

1). 0.30
2). 0.00
3). 0.02
4). 0.35
5). 0.02
6). 0.01
7). 0.02
8). 0.17
9). 0.13
10). 0.07
11). 0.57
12). 0.02
13). 0.04
14). 0.03
15). 0.16
16). 0.06
17). 2.28
18). 0.60
19). 0.03
20). 0.02
21). 0.02
22). 0.00
23). 0.90
24). 0.63

Total: 6.45″
( Rain 22 of 24 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″

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:

To the Actual Inland Path followed by Florence:

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.