Mountain Area Forecast ( March 13-15 )
ALERT For Accumulating Snowfall For Monday Night Into Tuesday AM At Elevations Above 2000-2500 Feet
Rain & snow will develop across the mountain area Monday night, followed by a change to all snow from the top down into Tuesday morning. Snow levels are expected to drop toward 2000-2500 feet. This will be a high density ( wet ) snow, with rain-snow mix or rain expected across lower elevations.
ALERT For Bitterly Cold Temperatures-Wind Chills And Intense Bursts Of Heavy Snow Late Tuesday Into Wednesday Morning With NW Upslope Flow
Colder air and widespread snow showers and local snow squalls are expected to develop Tuesday afternoon into Wednesday AM. Bursts of heavy ( whiteout type ) snow is likely Tuesday Night into Wednesday AM with NW Upslope Flow and very cold air aloft. This will be a low density ( dry ) snow at all elevations. An additional 1″ to 4″ of snow will be possible ( areas along the upslope side of the mountains which missed the wet snow into Tuesday AM will have accumulations Tuesday night into Wednesday ).
Overnight Into Monday Morning
Partly cloudy ( high clouds ). SSE winds increasing to 5-10 mph, with higher gusts, along mountain ridges-plateaus below 2700 feet. SSE-SSW winds 10-20 mph, with higher gusts, along mountain ridges above 2700 feet. Temps from around 20 degrees in colder locations to around 30 degrees. Wind chills in the 10s & 20s along higher mountain ridges.
Monday Afternoon – Updated
Becoming cloudy. Winds SE to SSE at 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges & plateaus. Temperatures varying from upper 30s to lower 40s at the highest elevations to the lower-middle 50s.
Monday Night Into Mid-Morning Tuesday
Rain changing to heavy, wet snow above 2000-2500 feet. Rain & snow at elevations below 1500-2000 feet. Light and variable winds shifting WNW to NW and increasing to 10-20 mph, with higher gusts, by morning. Temps dropping into the lower 20s to lower 30s ( coldest at highest elevations ). Wind chills from single digits & 10s at upper elevations to the 20s at middle and lower elevations.
Tuesday Afternoon-Early Evening
Mostly cloudy. Colder. A chance of snow showers-flurries. Temperatures steady or slowly falling into the 20s at mid elevations, into the 10s at upper elevations, and to around freezing at low elevations by late afternoon-early evening. Winds NW at 10-20 mph, with higher gusts. Wind chills plunging into the single digits & 10s by late afternoon, except below zero at highest elevations.
Tuesday Night Into Mid-Day Wednesday
Widespread snow showers, flurries and snow squalls. Bursts of intense snow possible. Turning bitterly cold. Winds NW at 10-20 mph, with higher gusts. Temperatures dropping into the single digits at highest elevations and into the 10s at middle-lower elevations ( along and north to northwest of the High Knob Massif-Tennessee Valley Divide, somewhat milder lee of mountains into the Great Valley ). Wind chills from 0 to 15 degrees below 3000 feet and from 0 to -15 degrees below zero above 3000 feet.
Becoming sunny. Cold. WNW-NW winds 10-20 mph, with higher gusts. Temperatures varying from the 10s in upper elevations to the 20s to around 30 degrees at middle-lower elevations. Wind chills in the single digits and 10s, except below zero in gusts at upper elevations ( above 3000 feet ).
*Snow Depth Forecast ( March 13-15 )
2″ or less below 2000 feet
( along upslope side of mountains )
2″ to 4″ at 2000 to 3000 feet
4″ to 8″ above 3000 feet
Little to no accumulation is expected lee of mountains into river valleys of the Clinch, Powell & Holston, with possible exception of cold air ( instability ) supported snow bursts.
Target snow depth of 3″ in Norton-Wise ( +/- ) 1″ error potential. This implies that 2″ to 4″ will be possible in the Norton-Wise area above 2000 feet elevation, with lower amounts below this level.
*Total snowfall amounts will be greater than snow depths in most all places due to melting, settlement, compression and other factors.
Weather Discussion ( Winter Storm )
Tuesday Overnight Update
Sticking snow levels dropped, as expected, down into the 2000 to 2500 foot elevation zone into the overnight with mountain ridges in Dickenson County and much of central-southern Wise County having accumulations.
The greatest accumulations occurred at upper elevations in the High Knob Massif where up to 4″ or more of snow stuck at highest elevations ( especially in the woods & on grass ).
New snow showers and flurries will develop in coming hours but the main action is looking to develop by late Tuesday into Wednesday morning when very cold air aloft and moderately strong NW Upslope Flow will combine with Great Lake moisture to generate widespread snow showers and snow squalls, with intense bursts of snow likely, as both temperatures and wind chills plunge to bitter levels.
Monday Evening Update
Wet snow has been pouring down on Eagle Knob of the High Knob Massif through the evening with the greatest amounts sticking to the grass and leaves.
As of 10:00 PM roads on Eagle Knob and High Knob are snow covered ( roads were last to have sticking ), with this view above looking across the roadway on Eagle Knob.
*As of Midnight several inches of snow accumulation has been reported atop the High Knob Massif. And it is pouring down!
Monday Afternoon Update
I have updated the forecast to account for latest model trends and conditions which show a slower development of precipitation and warmer afternoon temperatures.
The only other change includes a slight downward adjustment in forecast snowfall amounts & depths.
Forecasters in the southern Appalachians have had a rough time trying to pin down this late season winter storm. It is now coming as a hybrid Miller B + Miller A storm that will transition into a 977 mb ( 28.85″ ) bomb by late Tuesday along the New England coastline.
At this time of year a notable factor in most winter storms is elevation, with an elevation bias expected to dominate the first part of this event when wet snow will develop by late Tuesday into Wednesday morning. This is likely to be heavy, wet snow.
There remains a considerable spread in model forecast snow amounts, with little snow being predicted by the GFS Model west of the Eastern Continental Divide. This solution is for now being rejected given close agreement between the NAM and European models as well as past climatology of similar hybrid to bomb events.
*A similar storm with a hybrid A+B to bomb evolution during March 2013 resulted in a general 2″ to 6″ of snow across the area. That system was weaker and the Great Lakes not as free of ice.
With dry air currently in place there will be a considerable evaporative cooling potential with onset of virga and then precipitation later Tuesday.
There still remains a considerable error potential during this event, more than I have allowed for in forecast snow depths given a couple of factors:
Phase 1 – The Wet Snow Period: While heavy, wet snow is nearly certain at upper elevations, above 3000 to 3500 feet, the bottom limit or level of accumulating snow during this period remains only a best estimate. Right now I am going with the idea of wet snow sticking above 2000 feet.
However, if a northerly component develops in low-levels this could combine with significant +UVV ( upward vertical motion aloft ) to drop snow levels more than I indicate for locations along and north of the High Knob Massif where low-level air will be forced to rise ( if that happens then locations like Pound and Clintwood could get into sticking snow Tuesday Night into Wednesday morning versus only rain-snow and little to no accumulation ).
Phase 2 – The Dry Snow Period: This period is easiest with respect to precipitation type as air will be turning bitterly cold and all elevations will have precipitation which falls in the form of snow.
The wild card or unknown during this time period is the amount of Great Lake moisture reaching the mountains. Are forecast models resolving the fact of the Great Lakes being completely ICE FREE. If not, then snowfall amounts during this period could be more than I have indicated. At the least, it is nearly certain that snow will be widespread along the upslope side of the mountains with respect to NW flow during Tuesday Night into Wednesday morning.
Embedded within widespread snow showers and flurries will be snow squalls and the potential for streaks of snow. Given a combination of steep lapse rates with very cold air aloft + moisture in the prime dendritic snow crystal growth zone + moderate ( at least ) orographic forcing…the result will be bursts of intense snow. Local thundersnow would certainly not be out of the question in this type of setting.
The other big story will be the COLD. This is going to be a very cold week versus average for March, with the core of greatest temp anomalies centered over the Ohio Valley and southern-central Appalachians. “Shiver all me timbers.”