My Forecast For Today ( February 21 )

ALERT For Areas of Dense Fog & Low Cloud Bases Along And Southwest Of The High Knob Massif & Tennessee Valley Divide Overnight Into Sunday On SW Flow

*As of 12:30 AM on February 21 dense fog was widespread at elevations above 2800-2900 feet ( but will be locally lower in favored upslope locations on gusty SW winds ).

Dense fog ( orographic clouds ) has formed on SW Upslope Flow tonight and will be most favored for locations along & southwest of the High Knob Massif and Tennessee Valley Divide into Sunday as rainfall develops ( e.g., from the Wise area southwest along the U.S. 23 corridor toward Big Stone Gap where funneling of SW air flow tends to lower bases into Little Stone Mountain Gap and the Powell Valley Overlook section.  Caution is Advised for travelers ).

Thunderstorms Will Be Possible Today, Embedded In The Rain Shield.  Caution Is Advised For Lightning.

 Strong Rises Will Be Possible On Steep Creeks That Drain The High Knob Massif, Where Snow Melt Has Stream Levels Above Average At The Current Time.

ALERT For Dense Fog Formation From Late Sunday Night Into Monday At Middle-Upper Elevations Along And North Of The High Knob Massif-Tennessee Valley Divide On NNW-NE Upslope Flow

While any location could have fog after rain develops Sunday, the above ALERT is for widespread drops in cloud bases with northerly upslope flow behind a cold front late Sunday Night into Monday.  

Very dense fog is expected to develop along and northward of the High Knob Massif and Tennessee Valley Divide toward Midnight into the overnight-sunrise period of Monday.

Overnight Into Sunday Morning

Low clouds.  Areas of dense fog & drizzle.  A chance of light rain developing.  SW winds 5-15 mph, with higher gusts, on mountain ridges-plateaus below 2700 feet.  SW winds 10-20 mph, with higher gusts, along upper elevation mountain ridges.  Temperatures varying from the middle 40s to the lower 50s ( coolest at higher elevations and in sheltered valleys with light winds ).  Wind chills in the 40s, except some 30s at highest elevations in gusts.

This Morning Through This Afternoon

Rain.  A chance for thunder.  Locally heavy rain possible.  Rain becoming showery in nature late.  SW-WSW winds at 10-20 mph, with higher gusts, along mid-upper elevation mountain ridges & plateaus.  Areas of fog.  Temperatures varying from the upper 40s to upper 50s.

Tonight Into Monday Morning

Rain & showers tapering to drizzle.  W-WSW winds 5-15 mph, with higher gusts, shifting NNW-NNE.  Cloud bases dropping to obscure middle elevations in dense fog ( chance for freezing fog-drizzle at highest elevations amid the High Knob Massif by morning ).  Temperatures dropping into the lower 30s to lower-middle 40s by morning ( coldest at the highest elevations ).

A Major Winter Storm system will impact the mountain region during the February 24-26 period with strong winds, rain and a potential for significant NW Upslope Flow snowfall.  Stay tuned for updates on this developing storm system.

Reference my latest 022016 Extended Outlook for more details.

 

Weather Discussion ( February 20-21 )

An interesting setting was on display Saturday afternoon as widespread cloudiness along-south of the High Knob Massif was in contrast to partly sunny skies to the north.

Upslope flow across the still snow covered High Knob Massif allowed cloud bases to obscure upper elevations and form a very nice and persistent capping cloud mass.

Conditions inside the capping cloud mass featured dense fog and air temperatures in the mid-upper 40s.  Snow cover remained solid and deeper across northern slopes, with a little bare ground being visible along wind swept crest lines ( as on Eagle Knob below ).

Continuing melt of the previously 10″ to 20″ snowpack is keeping stream levels elevated, above average, on steep creeks draining the High Knob Massif tonight.

While forecast models predict the heaviest rain today to remain north of the area, along the surface low pressure track, any downpours ( especially if convective in nature ) could quickly raise these already elevated stream levels.

There will be potential for orographic enhancement on SW-WSW flow into the High Knob Massif area, as suggested by the NAM 4 KM Model along the Appalachians ( it tends to under-estimate enhancement in the High Knob Massif ).

The Bottom line – While no flood watches are officially in effect it will be wise for everyone living and driving along these already elevated steep creeks to monitor water levels today ( especially if rainfall becomes heavy with thunder ).

The focus by later tonight into Monday will be on a drop in cloud bases with upsloping northerly air flow that will be forced to rise upward from the Kentucky foothills into the High Knob Massif and Tennessee Valley Divide.

Depending upon how long the NW-NE air flow persists, low cloud bases & dense fog could be a factor for Wise and many other sites across Wise, Dickenson, and extreme northern Scott counties well into Monday ( worst case scenario being all day into the evening ).

Have a great Sunday.