112916 Forecast

Mountain Area Forecast ( Nov 27-29 )


ALERT For High ( ROARING ) SSE-SSW Winds Monday Into Monday Night.  Wind Gusts Of 40-60+ MPH Will Become Likely By Late Monday.  Caution Is Advised.

Tune Into NOAA Weather Radio And Your Favorite Media Sources For National Weather Service Watches, Warnings & Advisories.
Another period of STRONG winds will become likely Tuesday Night Into Wednesday.  Check back for updates.
Rainfall amounts by late Wednesday Into Thursday ( November 30 to December 1 ) could be enough to cause strong rises along creeks and streams, with enhancement expected to be greatest in favored orographic forcing zones along the Cumberland Mountains and the adjoining Cumberland Plateau into Tennessee ( esp. Wednesday ).

Overnight Into Sunday Morning

Mostly clear.  Cold.  Winds becoming light & variable, except along upper elevation mountain ridges where WSW-WNW winds of 5-10 mph will occur.  Temperatures varying from the 10s to mid 20s ( 10-15 in colder valleys versus steady or slowing rising temperatures along highest ridges into the 30s overnight into morning ).

Sunday Afternoon

Partly-mostly sunny ( high clouds ).  Milder.  Light SSW-SW winds increasing to 5-15 mph by sunset.  Temps from the mid-upper 40s to the mid-upper 50s ( coolest at highest elevations ).

Sunday Night Into Monday Morning

Increasing mid-high altitude clouds.  S winds 5-15 mph, with higher gusts, along mountain ridges below 2700 feet.  Winds SSW-SW 10-20 mph, with higher gusts, along upper elevation mountain ridges.  Temperatures varying from the upper 20s to lower 30s in colder valleys to the mid-upper 40s along exposed mountain ridges ( wind chills in the 20s and 30s on ridges ).

Monday Afternoon

Mostly cloudy.  Becoming windy.  SSE winds 15-25 mph, with higher gusts, below 2700 feet.  Winds SSE to S 25-35 mph, with higher gusts, on mountain ridges above 2700 feet.  Winds could gust over 50 mph at high elevations and with any mountain waves that develop.  Temperatures varying from 40s in the upper elevations to the 50s at lower-middle elevations.

Monday Night Into Tuesday Morning

 Cloud bases lowering-thickening with rain developing.  Periods of locally heavy rain possible.  Windy.  Winds SSE-S at 20-40 mph, with higher gusts, shifting SW by morning.  Temperatures steady or slowing rising in the 50s.  Winds could gust over 50 mph at high elevations and with any mountain waves that may develop ( esp. Monday Night ).

A second wave of heavier rainfall is currently expected to impact the mountain area on Wednesday.  Rainfall amounts may need to be closely followed, with strong rises possible along streams.  Stay tuned for later updates on this heavy rainfall potential.


Weather Discussion ( Significant Rain )

Sunday Evening Update

NAM 12 KM Model Total Rainfall Forecast
NAM 12 KM Model Total Rainfall Forecast – Sunday Morning Run

While there remains some run-to-run differences on rainfall amounts, models have settled on a significant rainfall event during the Tuesday-Wednesday period.

NAM 12 KM Model Total Rainfall Forecast
NAM 12 KM Model Total Rainfall Forecast – Sunday Evening Run

Orographic forcing will enhance amounts in favored places, such as the High Knob Massif where forecast trajectories are close to the long-term MEAN climatological air flow within the 925-850 MB zone ( esp. into Wednesday ).

*Although some models are splitting rainfall nearly evenly between the two waves, the second wave is likely to be most productive given that the atmosphere will ( by then ) be wet, saturated in nature and more unstable than initially.


Previous Discussion

Although Saturday temperatures struggled to break the freezing point at high elevations in the High Knob Massif, following morning riming on high peaks, the air mass will be changing in coming days as temperatures-dewpoints rise in advance of a couple waves of significant rainfall.

NW Flow Mountain Waves - November 26, 2016
NW Flow Mountain Waves – November 26, 2016
Air rises and the cloud thickens amid the ridge of each wave, while the cloud thins as air sinks into the trough of each wave ( think of oceans waves, except these are flowing through the fluid atmosphere ).
NW Flow mountain waves were prolific on Saturday, before moisture decreased by later in the day, with a couple dozen or more being counted on NASA visible imagery across the main generation zone from the VA-KY border to the TN-NC border.

Meanwhile, with clear skies and decoupled winds many mountain valleys will drop into the 10s by Sunday morning, with coldest valleys already in the 10s as of Midnight.  This is in contrast to temperatures which are rising into the 30s along higher mountain ridges ( from evening 20s ).

NAM 12 KM Model Total Rainfall Forecast
NAM 12 KM Model Total Rainfall Forecast Up To 7 AM Wednesday ( Nov 30 )

The main story this week will be the shift into a wet pattern that brings a couple waves of significant rainfall.  Heaviest rains are expected on Wednesday, just beyond the time of the above graphic.  It will be important to tune back in as this event comes into range of short-range models.

The European Model and its Ensemble MEAN has been very consistent in showing the heaviest wave of rain developing Wednesday into early Thursday, boosting totals.  Although precipitation spreads are large, varying from just under 1.00″ upward to 6.00″ on the 51-Members at the Wise ( KLNP ) gridpoint, the MEAN is around 2.00″ to imply that local amounts will be greater ( as also is well supported by local climatology ).

The development of ROARING SSE-SSW winds later Monday into early Tuesday will signal the upcoming rain event.