030616 Forecast

My Weekend Forecast ( March 5-6 )

Reference my 030416 Forecast for details on this past day.

ALERT For Dense Fog & Freezing Fog At Mid-Upper Elevations Along & North Of The High Knob Massif Tonight Into Sunday AM – Mainly Above 2700 Feet

Some freezing fog coated higher elevations around Norton-Wise into Saturday morning, with another round of dense fog expected to develop overnight into Sunday morning with freezing levels at the 2000 to 2500 feet elevation by morning ( new models tonight have lowered the freezing level by a few hundred vertical feet ) as deep northerly flow develops into Sunday morning.  This will also support some snow showers across upper elevations and drizzle and/or freezing drizzle-snow-mix at middle elevations and just drizzle at lower elevations ( mainly north of High Knob Massif ).
*This will develop on northerly upslope flow with downslope sites mainly having dry and mostly cloudy conditions.
New Snow Accumulation Saturday PM on Eagle Knob
New Snow Accumulation Saturday PM on Eagle Knob – March 5, 2016
*Snow fell hard, with big flakes, between 3:00 to 4:00 PM and covered roads at highest elevations for a time before melting  some, as the temperature hovered between 32 to 33 degrees.
While a rain-snow mixture fell in Norton-Wise during Saturday afternoon, mostly all snow fell at summit levels of the High Knob Massif with around 0.5″ accumulating on Eagle Knob through late afternoon ( new snow accumulation shown above ).  Tonight very dense fog ( freezing fog ) has settled into the high country with dropping cloud bases expected into middle elevations after Midnight into Sunday morning.  Slow down and take it easy.

Saturday Forecast

Mostly cloudy skies overnight will carry into this morning, with some breaks possible.  This has allowed dense fog to develop with temperatures below freezing.  Light northerly winds will shift SW-SSW by morning on middle to upper elevation ridges and will eventually help dissipate the fog.

Any sunshine will be limited today as mid to high altitude clouds begin increasing in advance of the next fast moving system.  Morning temperatures in the 20s to near 30 will have a chance to rise into the 40s across much of the area before afternoon rain showers develop.  The exception will be at higher elevations in the High Knob Massif where 30s prevail, with snow or a rain-snow mix being possible there.

*As it turned out sleet & snow, with a little rain mixed, fell in the 3000-3500 foot elevation zone with nearly all snow above 3500 ft.

Saturday Night Into Sunday Morning

Eagle Knob of High Knob Massif at 11:00 PM
Eagle Knob of High Knob Massif at 11:00 PM – March 5, 2016
Following late afternoon-early evening melting off roads, it took little time for snow to recover roadways at high elevations in the High Knob Massif during Saturday Night with another burst of heavy snow ( with riming in clouds and temps in the 20s on N winds producing wind chills as cold as the low-mid 10s ).

Winds will shift NW-NNE behind a cold frontal passage on Saturday evening, with rain showers becoming mixed with or changing to snow in middle elevations, and all snow at upper elevations.  Any snow accumulations, with up to 2″, look to be mostly above 2700-3300 feet in elevation.

A lowering of cloud bases will need to be watched for overnight into Sunday morning on northerly upsloping winds of 5-15 mph, with higher gusts, across mid-upper elevation mountain ridges-plateaus ( in typical locations along and north of the High Knob Massif and Tennessee Valley Divide…such as Wise, Sandy Ridge and adjacent communities which typically have dense upslope fog ).

Freezing fog will be possible at elevations above 2700 feet, with drizzle-freezing drizzle and/or some snow-mix at the lower-middle elevations and snow showers above 3000 ft.


Mid-Morning Sunday Through Sunday Afternoon 

Cloud bases are expected to lift and drier air is currently predicted to overspread the area into the afternoon with skies becoming sunny to mostly sunny.

Winds will become light and temperatures should rise into the 40s to low-mid 50s ( upper 30s to lower 40s over a little snow at highest elevations in the High Knob Massif ).


Sunday Night Into Monday Morning

Some mid-high clouds will be possible as winds will be shifting SSE-SW at 5-15 mph, with higher gusts, across middle-upper elevation mountain ridges & plateaus.

This wind shift marks the beginning of a long awaited warming trend, with temperatures rising at highest elevations overnight into Monday morning.

*Due to an increase in wind chills, this initial warming will not really be felt along mountain ridges ( that comes next week ).

Updated at 9:45 PM on Sunday – March 6, 2016

A large vertical temperature spread, as I originally expected, will develop through tonight into Monday morning with readings varying from frosty, cold 20s  within mountain valleys to upper 30s & 40s across exposed mountain ridges & plateaus ( where the off-setting factor will be an increase in wind chills, especially amid upper elevations where SSE-SSW winds are already gusty ). 


Weekend Summary

Seasonably cold conditions will continue to be felt through most of this weekend before a prolonged warming trend develops next week.

Clouds will remain abundant through Sunday AM, with another fast moving disturbance expected to spread rain and snow showers across the area from Saturday afternoon into Saturday night.

Any sticking snow is likely to be restricted to highest elevations, above 3300 feet in elevation ( dusting up to 2″ or so will be possible at these highest elevations ).

A period where cloud bases will drop needs to be respected by the Midnight-Sunrise period Sunday, when northerly upslope flow will develop.

A period of dense fog, with freezing fog above 2700 feet, will become possible at mid-upper elevations along and north of the High Knob Massif during a period between 10 PM Saturday & 10 AM Sunday.

The elevation of cloud bases ( dense fog ) and the freezing level will need to be updated later as this period gets closer in time.
The main idea being that cloud bases will drop again on upslope flow during late Saturday evening into Sunday morning, with riming and dense fog at upper elevations along and north of the High Knob Massif-Tennessee Valley Divide which may drop into middle elevations ( below 3000 feet ) for a period of time.

Cloud bases are expected to lift and finally dissipate  to produce mostly sunny to sunny skies into Sunday afternoon.  This will allow temperatures to rise into lower-middle 50s in milder locations, with 40s most likely across upper elevations ( coolest over snow at highest elevations and northern slopes within the High Knob Massif ).

A large vertical temperature spread will be likely to develop Sunday Night into Monday morning as winds shift southerly to begin a long awaited and prolonged warming trend.  This will be indicated first at highest elevations where temperatures will tend to rise, after any initial evening declines, overnight into Monday.  Mountain valleys, by contrast, will have temp drops and develop much colder conditions than breezy to gusty ridges ( the offsetting factor for high ridges being an increase in wind chills into Monday AM ).


Extended Look At Next Week

An unseasonably warm period of weather, via a major shift in the upper air flow regime across the USA, is on tap for next week.  Eventually, this will include rises in humidity-dewpoint ( moisture ) levels and showers-thunderstorms ( by late next week-next weekend ).

European Ensembles MEAN 500 MB
European Ensembles MEAN 500 MB Height Anomalies: DAYS 1-5

The eastern USA trough is going to be replaced by ridging as the western ridge breaks down and gives way to troughing.

European Ensembles MEAN 500 MB Height Anomalies Forecast
European Ensembles MEAN 500 MB Height Anomalies: DAYS 6-10

This will bring needed precipitation to California and will set up a pattern featuring an excessive rainfall potential across the Lower Mississippi Valley.  The eastward extent initially being blocked by ridging in the Atlantic; however, over time this will likely give way enough to allow for rains to move into the Ohio-Tennessee valleys and Appalachians.

European Ensembles MEAN 850 MB
European Ensembles MEAN 850 MB TEMP Anomalies: DAYS 1-5

This will be such a warm period that it should trigger the first woodland wildflowers of the season to emerge, if not already in milder locations outside the mountains, such as Coltsfoot ( Tussilago farfara ) and Trout Lily ( Erythronium americanum ), along with a few other species.  Enjoy.

European Ensembles MEAN 850 MB
European Ensembles MEAN 850 MB TEMP Anomalies: DAYS 6-10

For those who suffer from pollen, it should also begin to increase some early tree pollens ( such as maples and the willows ) at lower-middle elevations.

Have a great weekend.