033117 Forecast

Mountain Area Forecast ( Mar 31-Apr 2 )

Chilly Conditions Are Expected To Continue Through Saturday Into Sunday Morning

Overnight Into Friday Morning

Showers & thunderstorms developing.  Downpours likely.  Windy.  SSE to SSW winds 10-25 mph, with higher gusts, shifting SW by morning.  Temperatures in the 50s to lower 60s, dropping into the upper 40s to middle 50s by morning.  Coolest at highest elevations.

Friday Afternoon

Mostly cloudy and cooler.  Chance of hit-miss showers.  Low clouds ( fog ) at the highest elevations.  Winds WSW-WNW 10-20 mph, with higher gusts.  Temperatures in the 50s to around 60 degrees at lower-middle elevations and in the 40s to around 50 degrees at upper elevations ( along and northwest to north of the High Knob Massif-Tennessee Valley Divide ).

Friday Night Into Saturday Morning

Cloudy and chilly.  A chance of light showers or drizzle.  Low clouds with dense fog at upper elevations.  WNW-NW winds 5-15 mph, with higher gusts.  Temperatures dropping into the low-mid 30s to low-mid 40s ( coolest within the highest elevations ).  Wind chills in the 20s and 30s along mid-upper elevation mountain ridges.

The potential for low-level temperature inversion development is being monitored for Saturday.  An inversion would hold low clouds ( dense fog at upper elevations ) over the mountain area through the day Saturday, with unseasonably cold conditions.
If the inversion mixes out ( breaks up ) conditions will turn partly cloudy and temperatures will be somewhat milder with sunshine.

Saturday Afternoon

Low clouds ( dense fog at upper elevations ).  Chance of drizzle.  Unseasonably cool.  NW to NNW winds 5-10 mph, with higher gusts.  Temperatures hovering in the 30s and 40s to near 50 degrees.  Coldest at highest elevations.

Saturday Night Into Sunday Morning

Becoming partly cloudy to clear.  Areas of dense fog at low-middle elevations.  Frost and freezing conditions in higher mountain valleys ( above 2500-3000 feet ).  Winds N-NE at 5-10 mph, with higher gusts, on middle to upper elevation mountain ridges.  Temperatures varying from 20s in colder valleys at higher elevations to readings rising into the 40s along highest mountain ridges ( otherwise, temperatures widespread in the 30s ).

*The potential for an unseasonably cold, wintry pattern is being monitored for the April 6-10 period.  Stay tuned for updates.


Weather Discussion ( Changeable )

The dawn of mid-spring, with April marking the middle month of Meteorological Spring, is looking to feature a changeable weather pattern.  Everything from spring thunderstorms to snow could occur in the mountains.

Bloodroot ( Sanguinaria canadensis ) Begins Blooming On March 29, 2017
Certainly such radical swings in weather conditions are typical in the mountains at this time of year.  Past climatology is full of all weather types, from record warmth to big falls of snow…such as observed during the great snowstorm of April 2-5 in 1987.

The next few days are likely to serve up quite a range in weather conditions, from warm winds and overnight showers and downpours in thunderstorms to chilly air Friday night through Saturday into Sunday morning.

HRRR Model Rainfall Forecast Next 15-Hours ( To 11:00 AM Friday – March 31 )

Beyond the potential for some thunderstorms to be strong or locally severe during the overnight, the most uncertain aspect of this short-term forecast period will be Saturday when some high resolution models are showing a rather classic low-level inversion setting.  If this develops it will trap low clouds over the mountains, with reinforcement by low-level N-NE upslope flow into the Cumberland range, to generate unseasonably cool ( cold ) conditions.

NAM Model Forecast Sounding Above Norton At 11:00 AM Saturday
Observe how the RED temperature line meets the GREEN dewpoint line on the left side of this forecast sounding ( above left ), with a SHARP turn to the right by the RED line.  This sharp right turn is a rise in temperature to mark the inversion whose bottom is shown just above the 850 MB level ( the top being around 800 MB to make the inversion layer at least 50 MB thick or 1600 feet in this case ).
By 8:00 PM Saturday ( below ) the RED-GREEN temp-dewpoint line meet only within a thin layer, increasing the chance that by this time ( before or after ) the cloud layer will mix out or break up.  All the dry air above signals that high mountain valleys will be prone to frosty conditions into Sunday morning, with lower to middle elevation valley frost dependent upon whether fog forms or not.
NAM Model Forecast Sounding Above Norton At 8:00 PM Saturday
Morning lows in the 30s to lower 40s ( 41 degrees in Clintwood ) into morning hours of March 30, within colder mountain valleys, signals that air cold enough for frost and sub-freezing conditions could be felt by Saturday Night into Sunday morning; however, at this time it looks most likely in higher valleys where formation of fog will be less likely ( at elevations above 2500-3000 feet ).  This will need to be updated for valleys at lower elevations.
European 51-Member Ensemble MEAN 500 MB Height Anomalies: Days 6-10

A temporary flip in the pattern across North America is looking more likely by the 6-10 day forecast period, with unseasonably cold conditions possible.  This is a trend that will need to be monitored through coming days as it would mean widespread sub-freezing conditions and even some late season snowfall ( i.e., should it evolve as currently shown by the Ensemble Mean ).

European 51-Member Ensemble MEAN 850 MB Temp Anomalies: Days 6-10

There is plenty of time for changes to occur in this extended pattern that might move it away from such a cold solution, so be sure to check back for later updates.