022216 Forecast

My Forecast For Today ( February 22 )

The Alert for Dense Fog has been cancelled due to drier air working into the lower-level northerly flow today.  Lowering clouds again are likely into this evening with a chance for some showers.

Overnight Into Mid-Morning Monday

Rain & showers tapering to drizzle.  W-WSW winds 5 to 15 mph, with higher gusts, shifting NNW to NNE.  Cloud bases dropping to obscure middle elevations in dense fog.  Temps dropping into the upper 30s to middle-upper 40s by morning ( coldest at the highest elevations ).

Mid-Morning Through This Afternoon

Mostly cloudy ( cloud bases may lift off middle elevations ), with a few breaks possible.  Light N-ENE winds at generally less than 10 mph.  Temperatures varying from low-mid 40s to the low-mid 50s ( coolest at highest elevations ).

*High-resolution Models continue to ease the rain shield farther north and northwest tonight, such that I have updated again for the widespread development of rain ( steady, soaking rainfall ).

Tonight Into Tuesday Morning ( Updated 8:00 PM )

Rain developing.  Becoming steady and soaking into the overnight, especially along and southeast of the VA-KY border.  Winds becoming ESE to SSE at 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges.  Temps widespread in the 40s ( dense fog developing in upper elevations – patchy fog other locations ), with some upper 30s to near 40 degrees atop the High Knob Massif.

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 snowfall.  Preliminary indications for heaviest snowfall amounts are at middle-upper elevations from Wednesday Night through Friday ( starting at highest elevations with snow levels dropping over time ) on SW to W-NW winds.
Low pressure will intensify & become very strong as it moves from Texas toward New York State and the eastern Great Lakes between Tuesday AM and Thursday AM.  Multiple facets with this powerful winter storm system include strong winds ( with mountain wave formation possible on SE-SSE flow ), heavy rain, and a transition to snow in the backside circulation.  No snowfall amounts have been forecast yet, and the “Major” aspect is due to this being the winter season with a potent low pressure formation, so yes, any way this is dissected, it will be a Major Winter Storm System.  Details are yet to be worked out, including specific snow amounts.  Stay tuned.


Weather Discussion ( February 21-22 )

Mid-Morning Update

A look at low-level moisture this morning reveals that drier air has worked into the area northwest of last night’s front, and my update is to cancel the dense fog advisory.

High Knob Massif Webcam
High Knob Massif Webcam – University Of Virginia’s College At Wise
Dissipation of low clouds has locally occurred to actually reveal summit levels of the High Knob Massif at 10:28 AM ( above ).
NASA Visible Image At 9:45 AM
NASA Visible Image At 9:45 AM on Monday – February 22, 2016

A look at the NAM Model sounding above Wise at 7 AM found most of the vertical column to be unsaturated, except right at the surface which has now been able to mix out.  An array of mid-high clouds remain aloft.

NAM Model Sounding Above Wise At 7 AM
NAM Model Sounding Above Wise At 7 AM on Monday – February 22, 2016

While cloud bases will drop again by this evening, with luck this will offer some breaks for hazy sunshine and somewhat milder PM temperatures that may break above 50 degrees at lower-middle elevations ( I have opened the range a little ).

Big Stony Creek Stream Level
Big Stony Creek Stream Level Up To 8:30 AM Monday – February 22, 2016

The latest stream level shows that steep creeks continue to gush with whitewater this morning in wake of recent snow melt and rainfall, with Big Stony Creek being near the 4.0 foot RED Alert Stage.  While levels should begin to drop by later today, caution is advised around slippery-rocky banks of these roaring creeks.


My Overnight Discussion

A damp and gloomy Sunday graced the mountains with rumbles of thunder, to boot, well in advance of a frontal boundary that is just now pushing across the Virginia stateline at 12:10 AM ( February 22 ).

An old mountain saying states…if it thunders in February it will frost on the same day in May!  So mark that down now, and time will tell how close it is to reality this year.
High Knob Massif Webcam
High Knob Massif Webcam – University Of Virginia’s College At Wise

Upper elevations in the High Knob Massif have been amid the clouds for the better part of 30 hours now, with many more hours to go before this dense fog will clear for any prolonged period of time.  High-resolution models are somewhat less aggressive in holding moisture in today, with only shallow moisture available that might have, given some luck, a chance to break up for a while.

NAM 12 KM Model Surface Map
NAM 12 KM Model Surface Forecast Chart At 1:00 PM This Afternoon
A problem, of course, in telling exactly how today will play out arises since this frontal boundary stalls out over the mountain region today.  One reason model runs tonight are a little milder than last night with the boundary barely clearing the High Knob Massif area into this afternoon ( being just east-southeast ).
NAM 4 KM Model Mean Sea Level Pressure Forecast
NAM 4 KM Model Mean Sea Level Pressure Forecast – 7 AM Wednesday ( Feb 24 )

The big show, of course, that will dominate this week will be an intense low pressure that rapidly deepens ( gets strong ) as it lifts out of Texas into the Ohio Valley.

This will be one of the strongest storm systems of the entire winter season, and presents classic formation.

NAM 12 KM Model 300 MB Forecast
NAM 12 KM Model 300 MB Forecast At 7 AM Wednesday – February 24, 2016

Doing some old school hand analysis, the phasing region for intense cyclogenesis really shows up well at 300 MB by 7 AM on Wednesday, with coupling between the Left Front Exit region of a Sub-tropical Jetstreak & the Right Rear Entrance sector of a Polar Jetstreak.  Large-scale divergence aloft will be evacuating mass, which by atmospheric compensation is replaced by inflow of air at low-levels where convergence and spin-up occurs amid intensifying low pressure.

Uccellini and Johnson Jestreak
Uccellini and Johnson Jestreak Schematic
The Interaction of Jet Streak Circulations during Heavy Snow Events
along the East Coast of the United States

For those wanting to learn more about how this works, the classic winter storm generation paper by Louis Uccellini and Paul Kocin from back in 1987 is a good point to start.

Uccellini and Johnson, 1979: The
Uccellini and Johnson, 1979: The Coupling of Upper-Lower Tropospheric Jetstreaks
Uccellini, L.W., and D.R. Johnson, 1979: The Coupling of Upper and Lower Tropospheric Jet Streaks and Implications for the Development of Severe Convective Storms.  Mon. Wea. Rev. 107, 682-703.

The isallobaric component of this ageostrophic wind equation, above, which I mathematically derived from scratch some time ago is an important part of driving this:

NAM 12 KM Model 850 MB Wind Field Forecast
NAM 12 KM Model 850 MB Wind Field Forecast – 7 AM Wednesday ( Feb 24, 2016 )

This monster winter storm system is going to become a wind machine, which means orographic forcing is going to crank ( remembering with forcing there is both positive and negative forcing generated ).  The setting above, being for a strongly positive Mountain Torque force as the mountains push back against the atmospheric wind field.

NAM 12 KM Model 850 MB
NAM 12 KM Model 850 MB TEMP-Wind Forecast – 7 PM Wednesday ( Feb 24 )

Cold air surges in from the southwest with rain changing to snow at higher elevations Wednesday Night.  Given plenty of low-level moisture and strong forcing there is no doubt significant snow will fall across upper elevations in the High Knob Massif with winds also later shifting W-NW.

NAM 12 KM Model Relative Humidity-Wind Streamline
NAM 12 KM Model Relative Humidity-Wind Streamline Forecast – 7 PM Feb 24
If this low had tracked farther south and eastward, instead of west and northwest, it would have been like the February 1985 Blizzard which required my friend Carl Henderson of Wise to be air lifted off Eagle Knob of High Knob after the storm ended.
*The late Carl Henderson was an electrical engineer at the Blue Ridge Public Transmitter Station on the summit.  Carl was a wonderful person and luckily had snowshoes, which he wore to reach a clearing where an Apache-Jet Helicopter landed to pick him up.  The extraction was needed since Carl was a diabetic and running out of medication ( plus he was also getting cold with minimal heat in the building ).  I’ve written about his adventure, which also was documented by newspapers.  I can not say enough good things about this man and his wife.  He made a positive difference in the world, and surely that is the best we can hope for.

Meanwhile, this will be no February 1985 blizzard but it will be a very intense & interesting ( dare I say ) storm to follow through coming days.

Have a great Monday.

My dense fog ALERT for Middle Elevations appears to have been right on target.  Please slow down and take it easy my friends!
High Knob Massif Webcam
High Knob Massif Webcam – University Of Virginia’s College At Wise