120916 Forecast

Mountain Area Forecast ( Dec 6-9 )

A Blast Of Bitter Cold Air & Wind Chills Will Strike The Mountains With Falling Temperatures Thursday Into Friday Morning.  Some Flurries And Snow Showers Will Be Possible But Any Accumulations Look Light.

Overnight Into Mid-Morning Tuesday

Cloudy.  Low cloud bases & dense fog at highest elevations.  Rain developing.  Downpours possible by the predawn and early morning.  Areas of fog becoming more widespread.  SE-S winds 5-10 mph, with higher gusts, along mountain ridges-plateaus below 2700 feet.  Winds SSE-SSW 10-20 mph, with higher gusts, on mountain ridges above 2700 feet.  Temperatures widespread in the 40s.  Wind chill factors in the 30s to around 40 degrees.

Mid-Morning Into Tuesday Afternoon

 Rain, with local downpours, giving way to showers during the mid-late afternoon.  Areas of fog.  Winds shifting SW to WNW at 5 to 15 mph, with higher gusts, at elevations below 2700 feet.  Winds SW-WNW 10-20 mph, with higher gusts, along mountain ridges above 2700 feet.  Temperatures varying from upper 30s to upper 40s.  Wind chill factors in the 30s ( locally below freezing on highest peaks in gusts ).

Tuesday Night Into Wednesday Morning

Cloudy and colder.  Cloud bases dropping to obscure mid-upper elevations along & north of the High Knob Massif and Tennessee Valley Divide.  Fog becoming freezing fog with riming in upper elevations ( above 3300 feet ).  NW-N winds 5-10 mph, with some higher gusts.  Temperatures dropping into the mid 20s to mid 30s ( coldest highest elevations ).

Wednesday Afternoon

Skies becoming partly to mostly sunny ( high clouds possible by mid-late afternoon ).  Light & variable winds.  Temps varying from low-mid 30s in upper elevations to the low-mid 40s ( warmer south into the Great Valley ).

Wednesday Night Into Mid-Morning Thursday

  High clouds early giving way to lowering clouds with a chance of valley rain showers-mix and mountain snow showers by morning.  Winds WNW-NNW 5-15 mph, with higher gusts, along mid-upper elevation mountain ridges.  Mountain valleys dropping into 20s before rising overnight toward morning with increasing clouds.  Mountain ridges falling to around freezing in mid-elevations and into the middle 20s in upper elevations.  Wind chills in 10s & 20s.

Thursday Afternoon

Becoming partly to mostly sunny.  Steady to slowly falling temperatures.  Winds WNW-NW at 10-20 mph, with higher gusts.  Temperatures dropping into the middle-upper 20s to lower-middle 30s by late afternoon, except into upper 10s to lower 20s atop highest peaks by late.  Wind chills in the 10s and 20s, except single digits on upper elevation mountain ridges ( milder leeward of mountains into the Great Valley ).

Thursday Night Into Friday Morning

Becoming mostly cloudy.  Turning bitter cold.  Chance of flurries and snow showers.  Winds WNW-NW 5-15 mph, with higher gusts.  Temperatures varying from single digits to lower 10s at highest elevations to the 10s to lower 20s.  Wind chills in the single digits & 10s, except locally below zero in gusts on highest mountain ridges.  Riming on upper elevation mountain ridges ( mainly above 3300 feet ).

 A dusting up to 1″ of snow will be possible, with some slick patches.  As of 5:30 AM Friday the air temperature was 9 degrees on Eagle Knob of the High Knob Massif ( wind chills of -5 to -10 degrees below zero are being reported in gusts above 4000 feet ).
Clouds, flurries and snow showers will remain likely into mid-morning before beginning to dissipate.


Weather Discussion ( Arctic Blast )

Tuesday Night Update

While my forecast was very good through Tuesday, I’ve had to do some major surgery on the next few days as models struggle with this first major arctic blast.  Small changes could result in some accumulating snow, but right now the consensus is for little to no accumulation as arctic air hits.

Meanwhile, another heavy rainfall event of up to 2.67″ atop Eagle Knob of the High Knob Massif since Sunday AM has whitewater rolling out of the massif, with the stream gauge on Big Stony Creek peaking at just 13″ below the flood stage.  This all has fallen following a literal flat-line ( below ) through Autumn 2016, with little variations on steep creeks.

A general 7.00″ to 8.00″ of total rainfall since November 26 in the massif has generated around 6 vertical feet of water level rise on Big Cherry Lake, and it is still rising.
Big Stony Creek Stream Gauge Since September 1, 2016
Big Stony Creek Stream Gauge Since September 1, 2016

Most of 2016 had abundant precipitation, with many surges in whitewater to ROARING levels during the January 1 to September 1 period ( below ) prior to the flat-lining.

Big Stony Creek Stream Gauge
Big Stony Creek Stream Gauge – January 1 to September 1, 2016
The biggest water flows coming with rain + melt down of winter snowpacks early in the year ( during Winter 2015-16 ).

Precipitation for 2016 has now reached into the 60.00″ to 65.00″+ range in upper elevations of the High Knob Massif, from Big Cherry Lake basin into High Knob Lake basin.


Previous Discussion

Another soaking rain Tuesday will give way to a brief shift into upsloping NW-N winds Tuesday Night into Wednesday Morning that will lower clouds bases once again along the windward slopes of the High Knob Massif-Tennessee Valley Divide, with another round of light riming possible at high elevations above 3300 feet.

Majestic Rime In High Knob Meadow - December 3
Majestic Rime In High Knob Meadow – December 3, 2016

Meanwhile, the HRRR Model seems to be doing best at picking up the orographic enhancement along windward slopes of the Cumberland Mountains ( High Knob Landform and the Tennessee Valley Divide ), Cumberland Plateau and Blue Ridge overnight into Tuesday.  Rainfall amounts in the favored upslope locations should range in the 1.00″ to 1.50″ category for this event ( potentially heavier, at least locally, pending the influence of upper dynamics ).

HRRR Model Rainfall Forecast
HRRR Model Rainfall Forecast Up To 3:00 PM Tuesday – December 6, 2016

The main focus during this forecast period is on a blast of arctic air pouring south from northwestern Canada into the USA, with arrival time here set for Thursday into Friday.

European Ensembles MEAN Sea Level Pressure
European Ensembles MEAN Sea Level Pressure Anomalies – 7 AM Thursday

This has now been well advertised for some time, especially by the European Ensembles, with a sprawling 1050 MB High Pressure across northwestern Canada.  Although relatively short-lived, this will be real deal arctic cold and will mean business for the time in which it grips the Appalachians.

NAM 12 KM Model Total Snowfall Forecast
NAM 12 KM Model Total Snowfall Forecast Up To 7 AM Friday

While cold is certain, the amount of snowfall remains in question with the best current thinking being for upper elevations to have the best opportunity for 1″ or more of accumulation.  Little to no accumulations are currently expected across lower elevations ( especially below elevations of 1500-2000 feet ).

Stay tuned as this potential will be updated.