My Forecast For Today ( February 24 )

ALERT For A Major Winter Storm Impacting The Mountain Region Wednesday-Friday Morning With Strong Winds, Rain, Possible Thunderstorms, And Significant Snow-Rime At Mid-Upper Elevations

The General Order For This Event

Rain showers & rain increase during the overnight.  Downpours will become possible, especially along upslope favored locales on SE to SSE winds.

Wind speeds increase at mid-upper elevations with potential for mountain wave development and impacts in valleys leeward of the High Knob Massif, Clinch Mountain, Pine & Black mountains in the overnight-morning hours of Wednesday.

A broken or solid line of downpours, with possible thunderstorms, is roughly timed to arrive from southwest to northeast during the sunrise to mid-day period ( around 8-9 AM for Norton-Wise ).

Any break then gives way to redevelopment of showers, with possible downpours ( thunder can not be ruled out ) along and just ahead of the surface cold front during Wednesday afternoon.

A sharp temperature drop occurs as winds become very strong and gusty ( ROARING ) across the area between 4:00 PM and 7:00 PM as the cold front passes.  I can not STRESS ENOUGH that WINDS Will ROAR along and behind this cold front.

Rain showers change to wind driven snow by late afternoon into the evening for locations along the Virginia-Kentucky border, with sticking starting first at highest elevations and working downward into middle-lower elevations over time.

Significant snow ( with riming in upper elevations ) is expected Thursday-Thursday Night into the predawn hours of Friday for middle-upper elevations.

Threat for severe thunderstorms remains relatively low, but shear will be so strong that a severe thunderstorm can not be ruled out ( with increasing threat for severe storms across central-eastern Virginia into the Carolinas today ).  

Due to such strong gradient winds and shear the main threat today, whether with thunder or not, remains wind damage for all locations in the mountain area.  This raises the potential for power outages and local tree damage.

Reference my 022316 Forecast for details which remain valid.

Overnight Into Mid-Morning Wednesday

Rain showers.  Becoming very windy along middle-upper elevation mountain ridges ( and in mountain wave zones ).  Downpours possible, with a chance of lightning-thunder into morning.  SE-SSE winds increasing to 10-25 mph, with higher gusts, on mountain ridges-plateaus below 2700 feet.  SSE winds 20-35 mph, with gusts 40-50+ mph, on upper elevation mountain ridges.  Unseasonably mild with temperatures in the 40s to middle 50s.

Mountain waves will become possible into Wednesday morning, with strong to locally severe wind gusts in favored breaking zones from Powell Valley in Wise County to the Clinch Valley of Russell-Tazewell counties ( and immediately next to the Kentucky side of Pine Mountain and Black Mountain ).  Some questions remain as to how an atypically low inversion level will impact these waves.

Due to 1.00″ to 1.50″ of rain during the past couple of days, any prolonged moderate rain or downpours will need to be respected through today until colder air arrives ( ponding of water in low lying and poor drainage areas, rises on streams, will need to be followed closely until after the cold front passes ).

A dramatic weather change will occur this afternoon along and behind a strong cold front, with ROARING winds as a very strong pressure gradient begins driving and funneling SW flow upslope through the High Knob Landform into the Norton-Wise area and adjacent locations.  This will be the windiest period for the entire area as a whole, with strong winds extending into the evening.

Mid-Morning Through This Afternoon

Showers redevelop following any brief break.  A chance for downpours.  Thunder possible.  ROARING WINDS develop in all locations along and behind a strong cold front.  Showers of rain change to snow late.  Winds shifting SSW-SW at 20-40 mph, with higher gusts.  Temps plunge from the 50s to around 60 degrees into the 30s to around 40 degrees by sunset to early evening.  Wind chills dip into the 20s.

Blowing snow and drifting will develop overnight into Thursday amid upper elevations in the High Knob Massif, along with rime formation at elevations above 3000 to 3500 feet.

Tonight Into Thursday Morning

Any rain showers changing to snow showers during the evening.  Snow overnight, heavy at times ( especially along and southwest of the High Knob Massif & Tennessee Valley Divide ).  Windy.  SW to W winds 15-30 mph, with higher gusts, at elevations below 2700 feet.  SW-W winds 20-35 mph, with higher gusts, along upper elevation mountain ridges.  Temps varying from lower 20s to lower 30s by morning ( coldest at highest elevations ).  Wind chills dropping into 10s & 20s, except single digits at high elevations in the High Knob Massif.

Snowfall Forecast For The February 24-26 Period

Target Snowfall of 4″ in Norton-Wise ( +/- ) 1.5″ Spread Potential.  This implies snowfall totals from 2.5″ to 5.5″ will be possible with variations expected on the ground due to an unfrozen, wet state day-time settlement-melting, and blowing by strong winds.

A general 4″ to 8″ of snow is expected above 3000 feet amid the High Knob high country, with locally higher totals possible.  Large ground depth variations are expected due to blowing and drifting at the highest elevations ( with significant rime formation ).

*In general this is expected to be an elevation biased event, with increasing snow depth with increasing elevation.  Snow squalls and/or snowstreaks that may develop Thursday could locally skew this general trend.

 

Weather Discussion ( February 23-24 )

Late Afternoon Update

It has been quite a weather day across the mountain area, with ROARING winds and ROARING water.  As of 6:00 PM it has gotten cold enough for the first flakes of snow to begin falling atop the High Knob Massif ( at summit levels ).

However, most of the snow will begin to come in later during the evening and into the overnight period and Thursday morning.

Meanwhile, it is very dangerous around trees as gusts are making them pop and crack.  I was just outside to hear it first hand, so please use caution in these high winds.

The only update to my forecast late this afternoon being to ease wind speeds up even more, than I had them before, for tonight.

Sustained winds between 20 and 30 mph have been common at middle to upper elevations this afternoon, with gusts topping the 50 mph barrier atop the High Knob Massif and Black Mountain.

Outside of any mountain wave gusts and roaring winds along high mountain crest lines, the real ROAR began in most places along and behind a mid-morning squall line with heavy rain that passed through the Norton-Wise & Clintwood-Pound area during the 9:15-10:15 AM period.

Winds have truly been a ROAR with many twigs, limbs, and other debris scattered across the area, including some trees.  Power outages have so far been localized ( thankfully ).

More than 1.00″ of rain since Midnight, upon already wet ground, has pushed steep creeks draining the High Knob Massif into a pounding ROAR.

As of 3:15 PM the Big Stony Creek stream gage showed the level was just 14″ below flood stage.  Similar conditions are occurring on South Fork of the Powell River and adjacent steep creeks from Clear Creek to Little Stony Creek.

With colder air now pouring into the mountain area, and showers of rain that will change to snow tonight at mid-upper elevations, these high stream levels should gradually drop ( but please use caution around these creeks and their slick-rocky banks ).

 

My Overnight Discussion

A beautiful array of mountain wave clouds developed along the High Knob Massif during Tuesday afternoon, even if the high winds aloft had not yet reached the surface in valleys.

I have labeled a few views to illustrate the different types of orographic clouds being generated.

It was magical to watch how the massif interacted with air flow to generate these magnificent clouds ( these views not doing them justice, as would seeing them via your eyes ).

While some clouds changed continuously with air flow rushing over the massif, other clouds held their forms and were long-lived in nature ( e.g., the orographic cap cloud mass and standing wave cloud which varied little in position over time ).

Observe the long-tail which developed around sunset on the wave cloud capping the massif ( below ).

This cloud later developed a fish-tail form, and it was a shame to see darkness fall with such beautiful wave clouds taking on these majestic shapes.

The CAM switched into IR Model for better night vision.

Focus now shifts to a powerhouse winter storm system that will impact weather into Friday.  Models have not changed much locally from what I highlighted in my discussion last night, with an increasing risk for severe thunderstorms and possible tornadoes from central-eastern Virginia south into central-eastern portions of the Carolina’s.

However, this area will have to closely watch a squall line of downpours ( with possible thunderstorms ) that is currently timed to move across far southwestern Virginia during the 7:00 AM to 10:00 AM period.

The 1:00 AM run of the High-Resolution Rapid Refresh ( HRRR ) Model has the squall line over Norton-Wise at 9:00 AM.  Timing could, of course, be off some but this is the current trend.

Downpours of heavy rain and strong to potentially severe gusts of wind will have to be watched for during this time given such strong winds roaring across the high mountain summits ( and aloft ).

There remains a period today when models want to allow some surface based convective available potential energy, called SBCAPE, to develop amid still strong shear.

It is the lack of instability through this morning that will greatly limit the severe potential ( and a inversion layer aloft ) relative to what it would be with this ( below ) if significant instability was present to form surface based convection ( which in this type of high shear environment would easily be capable of developing rotating updrafts ).

Shear and the magnitude of helicity relative to how a storm updraft could be driven to rotate becomes simply extreme by the predawn-morning hours of today, but instability is lacking ( thankfully ).  Still this does not rule out a severe thunderstorm developing into this morning and will tend  to increase the risk of strong-severe winds along a squall line which may move across the area this morning.

Models say that the southern portion of the Tennessee Valley will have the greatest severe thunderstorm potential heading into this morning, with the best overlap of shear and instability.

As time passes, we will have to see if this potential may work northeastward up the Great Valley and into the Mountain Empire in advance of the surface cold front to provide one more period where severe thunderstorms ( outside any morning squall line ) and/or severe downdrafts in showers will be possible.

Clearly the best overlap of shear and instability will be developing east of the mountains by later this afternoon-evening into central portions of Virginia & the Carolina’s.

A severe outbreak could develop there as snow begins to fall atop the High Knob Massif, which, by no coincidence, has happened during past events as well documented by climatology.

One change from yesterday is that models are a little faster in bringing in the cold air, with the 0 degree ( 32 F ) freezing line overspreading far southwestern Virginia between 4 PM and 7 PM, on simply ROARING SW winds along and behind a strong cold front.  It would not be impossible to go from rain & thunder to snow in just a short time.

From this point onward it will be all about the wintry side of this storm system, with strong orographic forcing continuing into the Thursday Night-Friday AM period.  The flow being better for the City of Norton to get more snow than Wise, but time will tell about that ( as regards Norton vs. Wise snowfall totals ).

Stay tuned to NOAA weather radio for any possible warnings that may be needed through today.

Make it a great Wednesday.