Recap Of Forecast

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.

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.

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.

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 ).

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!

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 ).

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.

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

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.

Good luck and best wishes to all participants.