My Forecast For Today ( January 29 )

ALERT For Snow Shower & Local Snow Squall Development Overnight Into This Morning

Visibility will be reduced in heavier snow showers and any snow squalls which develop.  Roads in affected locations could quickly become slick & hazardous.  Remain Alert.

*State Route 619 remains extremely icy.  Chains are recommended if traveling across the High Knob Massif from the City of Norton to Fort Blackmore.  Hazardous conditions remain on other routes.

Overnight Into Mid-Morning

Lowering cloud bases with flurries and snow showers developing overnight into morning.  Snowstreaks and snow squalls possible.  Winds SW to WNW-NW at 10-20 mph, with higher gusts on middle-upper elevation ridges and plateaus.  Temperatures dropping into the upper 10s to upper 20s by sunrise to mid-morning.  Wind chill factors in the single digits and teens ( coldest at highest elevations ).

Snowfall Forecast For Friday

Upslope Side of Mountains
0.5″ to 3.0″

Downslope Side of Mountains
Dusting to 0.5″

Target snowfall of 1.0″ at Wise, ( +/- ) 0.5″ Error Potential.  This implies 0.5-1.5″ possible in the Norton-Wise area.  Extremes of a dusting up to 2-3″ will be possible across the area, with greatest snow amounts expected along upslope side of mountains with respect to WNW-NW air flow trajectories ( i.e., least snow likely ESE-SE of the High Knob Massif and Tennessee Valley Divide ).

This Afternoon

Any snow showers & squalls tapering to flurries & ending.  Cloudy skies becoming mostly sunny.  Cold.  WNW winds 5-15 mph, with higher gusts.  Temperatures varying from 20s to low 30s high elevations to the middle-upper 30s.  Milder south into river valleys of the Clinch, Powell, Holston and Great Valley of the Tri-Cities. Wind chills 10s & 20s.

Tonight Into Saturday Morning

Becoming mostly clear to partly cloudy.  A large vertical temperature spread developing between colder valleys and milder mountain ridges.  WNW winds shifting S to SSW at  5-10 mph along mountain ridges-plateaus below 2700 feet. SW-WSW winds 10-20 mph, with higher gusts, along upper elevation mountain ridges ( especially by morning ).  Temps dropping into the 10s to low 20s in colder valleys with calm winds verses rising readings through the 30s along mid-upper elevation ridges ( mainly above 2700-3000 feet ).

*Strong SW winds of 10-20 mph, with 30-40+ mph gusts, will become possible Saturday into Saturday Night across mid-upper elevation mountain ridges as warmer air is transported into the Cumberland Mountains ( conditions will feel much cooler than generally forecast, especially at higher elevations ).

 

Weather Discussion ( January 28-29 )

My Afternoon Update

This afternoon update documents my first missed snow forecast of this winter season ( it will remain above and be saved for later reference ).  The only current change was to update afternoon temperatures since with more sun and less cloudiness they have trended a little higher.

Even though this was to be a very weak event, a dusting to 0.5″, at the very most, is all that occurred along the upslope side of the mountains.

I typically look at a dozen or more different parameters when forecasting NW Flow snowfall.  However, of them all moisture is perhaps most critical since regardless of how good other factors are you can simply not get snow without sufficient moisture.

Moisture along and upstream of the high north-northwest facing slopes and crestlines is especially important in the generation of orographic snow on NW flow.  At 10:00 AM above, as one point selected, the 87% RH value came in well below the 96% value predicted by the 7 AM run of the NAM model this morning ( the GFS Model being very similar ).

The air never did saturate completely with orographic pilatus being limited and of short-duration during the morning, which limited riming.  Riming is a very important factor in enhancement of snowfall across upper elevations in the High Knob Massif where it adds to snow volume, in addition to its deposition and growth upon trees and other exposed objects ( as a secondary source of moisture that is visible until its drop…the rime enhancement of snowfall is visible only via close analysis and inspection ).

A major reason, of course, for the lesser amount of low-level moisture is that a calculation of backward air flow trajectories into Wise up to 7:00 AM reveal a miss with incoming air from a continental source region instead of the Great Lakes ( the above plot set for 500 meters above ground level with a 100 meter plot streaming in from mid-continent to an even greater extent ).

Vigorous morning snow showers moved through the Charleston area of West Virginia.  From space the difference is small between Wise & Charleston; however, on the ground the difference this AM was large since air flow into Charleston crossed the Great Lakes upstream ( illustrating, as has been well known here for decades, how important the Great Lakes are to NW Flow ( upslope ) snow in absence of wrap-around and all other moisture sources ).

Moisture streams off the Great Lakes are notoriously narrow in nature along the Lakes, and can remain that way downstream.  Hitting any given point from 400 air miles away then becomes a challenge if flow across the Lakes is not strong and vigorous and cyclonic in nature.

 

My Overnight Discussion

A significant spread in temperatures were observed across the mountain area during Thursday, as past climatology has dictated, with PM MAXS varying from low-mid 30s over the snowpack atop the High Knob Massif to middle 40s on SW downslope flow at Clintwood and upper 40s in Grundy.

A period of afternoon clouds featured more nice waves visible above the High Knob Massif area, with gusty SW winds making conditions feel like winter ( for certain ) across the higher terrain.

MAX temperatures in the upper 30s to lower 40s were common in the Norton-Wise area, in contrast to mid-upper 40s from Pound and Clintwood to Grundy.

NW winds tonight have been gusting over 30 mph recently along our high mountain crestlines.

This has occurred as the temperature begins to drop and moisture begins to increase ( below ).

Focus now shifts to the final cold air push of January 2016 which has been a relatively cold month in the mountains, with increasing overnight moisture to bring a final snow.

The NAM Model now predicts that the 925-850 MB flow field will come into alignment to bring a period of Great Lake moisture into the High Knob Massif area during the predawn to mid-morning period of this TGIF ( flow now being predicted to come farther south into the area verses previous model runs ).

Snow showers and flurries will develop with potential now for local squall and snowstreak development given this increased moisture in low-levels amid the upslope lifting zone.

The GFS Model streamline forecast predicts the same basic flow, which will be short-lived but potentially productive during a 6 hour or so period from the predawn into mid-morning.

I increased my previous snowfall forecast only slightly for the area in general, leaving my target snow forecast for Wise alone given uncertainty associated with where squalls and any narrow snowstreaks may hit ( the upslope area having widespread snow, but with embedded heavier bursts which are impossible to pinpoint since they are yet to form on Doppler ).

Snow flakes began falling on Eagle Knob of the High Knob Massif during the 2:00 to 2:30 AM period as an upper air disturbance passed and the atmosphere began to moisten.  The best low-level moisture not arriving until the predawn to mid-morning period when Doppler will begin to show a more classic upslope development of echoes as air rises upon approaching the Virginia-Kentucky border area.

With widespread old snow remaining on the ground, the upcoming day will be cold so bundle up, as this fresh batch of cold air arrives.

For those wanting a warm up, the good news is that cold air will begin retreating as soon as this upcoming overnight-Saturday morning period along highest mountain ridges of the Cumbelands; but, the bad news, is with increasingly strong winds from the SW which will drop chill factors to effectively delay true sensible warming for our middle-upper elevations until the late weekend and/or Monday.

As long as snow cover remains widespread it is hard to get really warm.  A major storm system next week still looks to generate a potential for strong winds ( and mountain waves ) along with the chance of strong-severe thunderstorms as the warmest air arrives by Tuesday ( February 2 ).  Stay tuned for updates.

 Have a great TGIF.