My Forecast For Today ( February 15 )

A Major Winter Storm Will Impact The Mountain Area With Multiple Threats Through Today Into Tuesday.  A Second Disturbance Will Then Renew The Chance For Significant Snow Late Tuesday Into Tuesday Night.

Let’s Try To Lay Out What Is Upcoming In Headlines:

Bands of moderate to heavy snow will give way to mixed precipitation into Monday AM to mid-day.

*Timing on the change from snow to mix-rain varies from the predawn to between sunrise and early afternoon.  This will be important to snow amounts, as a new wave of moisture over western-middle Tennessee & Kentucky moves into the area.

A change to all rain will become possible, with the potential for moderate-heavy rainfall  by later today.

*The potential for freezing rain will exist in any locations that remain below freezing ( of course ), and could even occur on surfaces which are very cold from 5+ days of sub-freezing conditions where air temperatures go above freezing.

*Other concerns that will need to be monitored include rainfall amounts and absorption by snow on roof-tops where significant weight could be added into tonight and Tuesday.  In addition, if rainfall becomes heavy, run-off issues could arise and this will need to be closely followed later today into tonight for poor drainage locations, roadways, and for rises on streams. 

A change back to snow, especially at middle to upper elevations above 2000 feet, will become possible by Tuesday Morning.  A period of heavy, wet snow will be possible during the morning, with greatest amounts expected at the highest elevations ( more than 3″ ).

*A surface low pressure will be intensifying along the eastern side of the Appalachians late tonight into Tuesday morning.  Models are not yet together on exactly how this plays out, but potential for a change to heavy, wet snow must be respected…especially from the Cumberland Mountains westward and northeastward.

It should be noted that the NAM Model is showing the type of development that is climatologically favorable for heavy snow in the Cumberland Mountains.  This has to be updated and followed very closely on new runs in coming hours.

A second system dropping into the mountain region will renew a threat for significant snow late Tuesday into Wednesday.

*If the above were not already enough, a second clipper system is forecast by models to race southeast into the base of this eastern USA upper air trough to renew the threat for a period of moderate to heavy snow late Tuesday into Tuesday night-Wednesday.

Overnight Into This Morning

Snow & blowing snow.  Heavy at times.  Possibly becoming mixed with sleet or freezing rain. SSE winds 5-15 mph, with higher gusts, on mid elevation mountain ridges-plateaus.  SSW-SW winds 15-25 mph, with higher gusts, along upper elevation mountain ridges.  Temps rising and becoming widespread in the 20s.  Wind chills in the 10s & 20s on exposed mid-upper elevation ridges & plateaus ( single digits in gusts along mid-upper elevation ridges ).

This Morning Through This Afternoon

Snow changing to rain ( possibly freezing in some places and upon very cold surfaces ).  SSE winds 5-15 mph, with higher gusts, on mid elevation mountain ridges-plateaus.  SSW-SW winds 15-25 mph, with higher gusts, along upper elevation mountain ridges.  Temperatures struggling to rise above freezing, especially over snow in valleys & along the highest windward ridges in the High Knob Massif ( mildest along exposed middle elevation ridges & plateaus ).

The forecast for tonight has been updated to include the increase in wind speeds shown by models.  Stay tuned for possible additional updates later tonight regarding snow potential for the predawn-sunrise period on Tuesday.

Tonight Into Tuesday Morning

Rain.  Heavy at times.  Rain may change to heavy, wet snow by morning ( especially mid-upper elevations ).  SSE winds increasing to 10-20 mph, with higher gusts, below 2700 ft.  SSE-SSW winds increasing to 20-35 mph, with gusts 40-50+ mph along upper elevation mountain ridges this evening.  Wind shifting WNW-NW in the predawn at 10-20 mph, with higher gusts.  Temperatures rising in the evening with 30s to lower 40s, then dropping during the predawn-morning back into the 20s to lower 30s.  New snow accumulations of 1″ to 3″ below 3000 feet, with 3″ or more above 3000 feet, along and north to northwest of Cumberland Mountains.

Many valleys outside of the mountain wave breaking zone will have much lighter winds.  Some could, in fact, remain under the current inversion which has dense fog and chilly temperatures over the snowpack.

At 7:45 PM the current official NWS temperature is 32.0 degrees in Clintwood.  Cold air has settled below an inversion layer through mountain valleys of this area, with fog and very light winds.

 

Weather Discussion ( February 14-15 )

My Afternoon Update

A break in the action this afternoon lets me see where we are at up to this point in the winter storm.  Yes, this point, there is much more to come ( especially for some ).

Observe the nice orographic wave clouds above the High Knob Massif this afternoon, with the summit level ( and back side in general in northern Scott County ) engulfed in the clouds.

At 2:00 PM a report from Joe & Darlene Fields finds 10″ of snow on the ground, with 6.0″ of new snow, at their home  in the High Chaparral community ( 3300 feet elevation ).

Around 7.5″ of new snow has fallen up at the summit level, with well over a foot of snow depth ( 12-18″ looks common ).  It has been a struggle to break above freezing.

Down below, in the City of Norton, snowfall was atypically less than often reported ( but well fits past climatology ), with Scott Craft & Caleb Ramsey measuring 3.7″ of new snow to 9:00 AM this morning ( 8″ of total snow depth ).

City of Norton Water Plant: 3.7″ new snow ( 0.43″ water content ) with 8″ of mean snow depth at 9:00 AM on February 15, 2016.

Up to 3:30 PM the PM MAX temperature had been 35.6 degrees at the City of Norton Water Plant.

In this case the 925-850 MB wind field was SSE-SSW across the High Knob Massif, with enhanced sinking air downward into the City of Norton.  Locations on the Scott County side of the massif have reported more, at lower elevations, than higher valleys on the Wise County side since low-level air was rising upward toward the massif from the SSE.  This helped enhance snowfall from Nickelsville to The Pines & Fort Blackmore of the Clinch River Valley.

Anna Hess reports 4.2″ of snow in The Pines area of the Clinch River Valley.

*The above setting being directly opposite to what occurs during NW Flow settings when enhanced snowfall is common in Norton with very little ( typically ) in the Clinch River Valley corridor.

Up to 10:00 AM today, my friend Chris Allgyer measured a total of 4.3″ of snowfall in Big Stone Gap.  While this was a “good” amount of snow for Big Stone Gap verses many NW and especially easterly ( when they truly get robbed ) flow settings, it was still significantly less than measured farther southwest along the Powell River Valley.

*Southwest of a Big Stone Gap to Pennington Gap corridor a SSE low-level flow undergoes much less sinking into the Powell River Valley as the southwestern flank of the High Knob Landform gets narrow and much lower in elevation ( i.e., Powell Mountain and Newman Ridge, with the interior Wallen Ridge also possessing a break southeast of The Cedars in Lee County ).

My friend Rodney Parsons measured 3.0″ of snow depth during Sunday up to the evening break.  He swept that off and by 10:00 AM Monday had 5″ new to bring the storm event tally to 8.0″ at his location near St. Charles.

Up to the north, in Clintwood, a total of 4.7″ of new snow has been measured so far during this event ( 6″ of depth ).  As of 4:50 PM the temperature in Clintwood is 34 degrees, down from a PM MAX of 36 degrees.  It is very foggy.

Wayne & Genevie Riner measured 5.8″ of snow up through their morning observation on Long Ridge of Sandy Ridge

Focus now shifts to what is next, with moderate-heavy rain expected tonight.  This will raise numerous concerns as the headlines at the top note.

Mainly adding weight to many roof-tops now having 4-8″ or more of depth, and the aspect of run-off into snow clogged drains, ditches, and roads where there could be enhanced ponding.  A flood watch is in effect through tonight.

In addition, models have increased wind speeds with very strong winds expected in upper elevations of the High Knob Massif and in mountain wave breaking zone amid localized places from Powell Valley in Wise County to Clinch Valley in Russell & Tazewell counties.  Wind gusts could top 50 mph in these places tonight.

There will be a transition to heavy, wet snow on the backside of the storm rain shield tonight into Tuesday morning.  This will begin in central Kentucky and wrap back into the Cumberland Mountains by morning.

The NAM Model has the snow band farther west, the GFS Model farther east, with the main idea being that rain will change to heavy, wet snow for a period of time along back of the rain shield into Tuesday morning.  This will need to be closely followed and updated again later tonight.

The best chance for significant snow on Tuesday Morning will be along and northwest to northeast of the Cumberland Mountains.

 

My Overnight Discussion

Reference my 021416 Forecast discussion for more details.

The most complex weather system of the 2015-16 winter season is making it hard on forecasters and models alike with large-scale rising motion over retreating arctic air.

Instead of coming together as one consolidated storm, this system is in open wave form with embedded disturbances that may finally congeal enough by late today to develop a more distinct area of low pressure ( as another upstream piece of energy dives southeast to continue the mayhem ).

The track of a developing surface low on the NAM Model, as well as the new European 16 KM Model, is one favoring the development of significant snow in the local mountains.

Should this occur, the window for purely rain will close rapidly as rain changes back to snow ( of course, assuming snow falling now makes the predicted transition to mix-rain into today, which all models currently agree upon ).  Whether all temperatures at the surface can rise above freezing is another story, that only time will determine.

Surface temperatures over snow are always problematic, with tendency toward inversion formation.  Only if strong winds aloft, and along the high mountain crest lines, can mix downward with vigor can most all surface temperatures rise above freezing.

The NAM Model predicts the entire area to be well above freezing by 1:00 PM today, with a CAD ( cold air damming ) wedge of low-level cold air hanging along eastern slopes of the mountains chain ( with warmer air aloft above that ).  Typically, with extensive snow cover, it is often not that clear cut and simple in this complex terrain.  Time will tell.

Temperatures over snow, with strong upsloping, into highest elevations of the High Knob Massif have also always been very problematic in these settings ( i.e., a struggle to get above 32 ).

The wave diving into the backside of this system looks rather impressive on the NAM Model, with strong upper diffluence ( divergence aloft ) and vorticity advection by late Tuesday into Tuesday night.  The European Model is a little slower than the NAM in digging this into the area.

The GFS Model has beat the NAM Model up to this point in the storm with respect to total snowfall.  It predicts that snowfall at the Wise gridpoint will increase by 4.9″ from this morning into early Thursday ( bulk coming during the Monday Night-Tuesday Morning transition back to snow ).  This is, of course, just a single model’s prediction.

One thing seems certain, an axis of heavy precipitation will develop by late today into tonight such that either way ( be it heavy rain or heavy rain to more heavy snow ) it will not be pleasant.  Stay tuned for updates later today.

It should be noted that the snowfall pattern during this event has been dominated by meso-scale snow bands, with indications of gravity waves ( linear features inside them ) as very strong winds aloft interact with the mountains and jet streams ( jet streaks ) aloft.

While I did not take time to draw a new snowfall map, my previous map holds as most places will be coming in amid upper portions of the ranges ( especially if more snow falls late tonight-Tuesday ).

Please try not to travel overnight into this morning if possible, giving VDOT time to work and temperatures time to rise from current levels well below freezing.