ALERT For Moderate To Heavy NW Upslope Flow Snowfall Monday Night Into Mid-Morning Tuesday
A upper air wave and significant moisture transport from the Great Lakes is likely to generate heavy upslope snowfall during Monday Night into Tuesday, especially along & west northwest of the Cumberland Front ( High Knob Massif and Tennessee Valley Divide ).
Locations along the west-northwest side of Clinch Mountain, as well as the secondary lifting zone from Mount Rogers southwest along the Tennessee-North Carolina stateline to the summit level of the Great Smokies are also included; however, the most widespread impacts will occur along and to the northwest of the Cumberland-Allegheny Front. Reference the end of this page for Mesoscale-Synoptic notes.
Bursts of intense snow are expected to reduce visibility and create hazardous driving conditions Monday Night into the overnight of Tuesday. Please use extreme caution.
Cold Air Is Expected Tuesday Into Wednesday Morning
Temperatures are currently expected to drop into the 10s to around 20 degrees on Tuesday Morning, with single digits to around 10 degrees at highest elevations. Wind chills will be significantly lower at mid-upper elevations.
The potential for the coldest temperatures to occur in mountain valleys is being monitored for Tuesday Night into Wednesday AM, with single digits and 10s. Local below zero readings will again be possible within coldest mountain valleys at upper elevations of the High Knob Massif ( especially if snow is on the ground ).
Sunday Night Into Monday Morning
Periods of Drizzle. Dense fog at mid-upper elevations above 2000-2500 ft, then cloud bases lifting at upper elevations. Areas of dense fog possibly developing or reforming at low-middle elevations. NNW-NNE winds 5-10 mph with higher gusts. Temperatures dropping into the 20s to around 30 by morning, coldest upper elevations. Wind chills dropping into the 20s to around 30 degrees, except 10s at highest elevations in gusts. Freezing fog at the highest elevations into overnight prior to clouds lifting.
Monday Morning Through The Afternoon
Low clouds giving way to a mid-high cloud-sun mix before increasing clouds during late afternoon. A chance of snow flurries or sprinkles late. WNW-NW winds 5-15 mph, with higher gusts. Temperatures varying from upper 20s to low 30s at highest elevations to the upper 30s to lower 40s. Wind chills in the 20s and 30s, except 10s high peaks.
Snowfall Forecast Through Mid-Morning Tuesday
2″ to 4″ along and north-northwest of the Cumberland Front, with locally higher amounts, especially at upper elevations within the High Knob Massif. A more narrow zone, along the secondary lifting zone, is expected with similar to somewhat less amounts from Mount Rogers southwest along the TN-NC border to the Smokies.
A dusting up to 1″ in downslope locations along the Powell, Clinch and Holston river valleys ( any bursts here being due to instability aloft and not orographic rise ).
Monday Night Into Mid-Morning Tuesday
Turning colder with snow showers & squalls. Bursts of intense snow. NW winds increasing to 10-20 mph, with higher gusts. Blowing-drifting at high elevations. Temps dropping into the 10s to lower 20s at low-middle elevations along and northwest of the Cumberland Front, with single digits to low 10s at upper elevations. Wind chills in the single digits to low 10s, except 0 to -15 below at upper elevations above 3000 feet. Rime formation at high elevations. Widespread hazardous travel conditions developing across the upslope zone.
Mid-Morning Tuesday Through Tuesday Afternoon
Snow showers & flurries gradually ending. Becoming partly to mostly sunny. Cold. NW winds 5 to 10 mph with higher gusts. Temperatures varying from mid-upper 10s to mid-upper 20s to around 30 degrees ( coldest upper elevations ). Wind chills in the 10s to low 20s, except single digits at highest elevations.
Tuesday Night Into Wednesday Morning
Mostly clear through the evening, then increasing mid-high clouds overnight into morning. Large vertical temperature spreads developing between frigid mountain valleys and rising temperatures on mountain ridges. Light & variable winds becoming SSE-SSW at 5-10 mph on ridges. Temps dropping into single digits & 10s, then rising on mountain ridges into the 20s overnight into morning. Local below zero temperatures possible in upper elevation valleys.
The potential for more heavy snow is being watched for the February 1-2 period, with additional waves expected to bring more snow by February 4-5 and beyond into next week. A very snowy period is upcoming for the mountain area.
Weather Discussion ( Very Active )
A very active ( energetic ) winter pattern will be returning to dominate the mountain landscape through coming days.
The initial priority features low cloud bases, drizzle, and dense fog through Sunday Night into Monday on northerly upslope flow and dropping temperatures.
A short break during Monday will feature a dissipation of low clouds as mid-high clouds appear overhead to signal the next weather system rapidly approaching. An increase in clouds will occur later Monday as bases begin to drop once more on increasing NW upslope flow.
Prime conditions develop Monday Night into Tuesday for snow showers & squalls. I expect heavy snow with intense bursts of whiteout type snowfall at times to greatly drop visibility and create hazardous driving conditions.
*There are likely to be many school delays and cancellations by Tuesday morning, especially in counties along and west of the Cumberland-Allegheny Front.
Good orographic forcing will be aided by steepening lapse rates and a passing upper wave to really help intensify the snow showers into squalls. For those unaware, this setting could really catch them off-guard so be warned now if you have travel plans Monday Night into Tuesday Morning.
Albedo will make certain that Tuesday is a cold day with continuation of low sun angles once the snow showers and flurries end and low clouds break. A rather classic setting follows into Tuesday Night with light winds and a plummet in temperatures over snow cover through the evening, this will be enhanced by warm advection aloft with a strong temperature inversion forming above valleys.
A couple examples, of many, from January 2018 of rapid evening temperature drops analogous to what is expected Tuesday evening in high valleys of the High Knob Massif are cited here ( with strong drops in all valleys, these just being part of our high country mesonet ).
Reference my 010618 Forecast in the “Previous Discussion” section to review the above period of time as I was forecasting it to occur. The above data was downloaded during a January 27 Field Trip with research students from UVA-Wise.
At Midnight on January 7 the temp was -8.4 degrees Fahrenheit below zero, with the following regional temperatures reported at the same time courtesy of the WCYB-TV 5 archive.
Beyond Wednesday the main focus will be on upstream waves in the jet stream that will threaten the mountain region with a potential winter storm. Right now it remains only a potential, but the totality of ensemble guidance from the European group suggests that a threat is justified. This should become clear by mid-week, so stay tuned.
The following was written Monday afternoon-early evening, then an internet outage prevented posting until near Midnight on January 29.
Mesoscale-Synoptic Forecast Notes – January 29
From my perspective this was the easiest winter forecast of the season, as it was very clear as to the result. That is far from being true regarding numerous NW flow settings in the southern Appalachians, with the main difficulty being marginal Great Lake air flow trajectories ( which can be calculated in reverse during and after events ).
11:00 PM Update: 2″ to 3″ of snow is on the ground at my official station in Clintwood. This snow was due to the cold frontal band and upper wave. Now the Great Lake moisture follows to continue snow into sunrise to mid-morning Tuesday when dry air will surge into the region to dissipate low-level moisture.
Remember, of course, my elevation is 1560 feet above mean sea level or just a bit higher than Tri-City Airport. The main difference being this location is embedded within the initial lifting zone with respect to NW flow trajectories, the main emphasis of these notes.
It is important to note that my use of terrain features is based upon 30 years of research, during which time the collection of data has demonstrated that the concept of lift should be applied in respect to orographic forcing based on which lifting zone should receive the most emphasis under what atmospheric conditions.
In the middle, bursts of snow, like observed in the Great Valley during this event tend to be dynamically supported via steep lapse rates and/or upper divergence and cyclonic vorticity advection. Once that departs the Great Valley is subjected to inverse forcing, which from an orographic viewpoint = downsloping to be overly simple.
These notes; however, are about orographic forcing and the primary and secondary lifting zones which it generates and some concepts that forecasters need to apply.
It is generally understood, for example, by forecasters that SE air flow streaming into the Blue Ridge generates heavier precipitation along the Blue Ridge escarpment versus more interior locations along the Blue Ridge ( Mount Mitchell and Grandfather Mountain tend to get more than mountains on a northeast-southwest transect through Mount LeConte on this type of flow, and Meadows of Dan tends to get more than Whitetop Mountain ).
Even through Meadows of Dan is significantly lower in elevation than Whitetop Mountain, the initial lifting of moist air along the flank of the Blue Ridge generates the heaviest precipitation on SE air flow trajectories in the MEAN ( there always can be exceptions during any particular weather event ). This is also the reason that southwestern North Carolina contains the wettest terrain in the southern-central Appalachians since it is situated in a position to obtain initial lifting of inflow from both the Gulf of Mexico as well as the Atlantic Ocean ( total mean annual precipitation tending to decrease with increasing distance from the zone of initial lift due in large part to increasing moisture extraction by orographics that force repeated rises and sinking of air along a flow trajectory ).
The Blue Ridge ( and especially its escarpment ) is the primary lifting zone with respect to SE flow trajectories. Leeward sinking generates an enhanced minimum in total precipitation along the Great Valley corridor, followed by an increase in amounts again along the secondary lifting zone of the Cumberland-Allegheny Front on SE flow.
The secondary lifting zone produces less total precip than the primary lifting zone, due in part to mountains being lower in mean elevation but also due to upstream moisture extraction along the primary lifting zone = less total moisture within a vertical column of the atmosphere to be precipitated out ( * ).
*While this is generally true, I have identified a unique winter circulation that appears indigenous to the High Knob Massif which greatly enhances snowfall on SE air flow trajectories under specific conditions. But that is not what these notes are about.
Flip this to NW flow. Since NW flow during winter is often cold, only snowfall will be considered. During NW flow the primary lifting zone is formed by those mountains & their adjacent foothills which are along & west of the southeast flank of the Cumberland-Allegheny Front.
During NW flow the Cumberland-Allegheny Front becomes the focus of the primary orographic lifting, and in the mean the greatest snow amounts with initial lifting ( the towns of Wise and Clintwood, for example, have higher annual snow totals than Big Meadows at the top of Shenandoah National Park even though they are much lower in elevation ).
Shenandoah National Park reports that 43 cm ( 37.0″ ) of snow falls annually in Big Meadows at 3500 feet above mean sea level versus around 112 cm ( 44″ ) at 1560 feet elevation in Clintwood, and up to 196-274 cm ( 77-108″ ) in the 3200-4200 foot elevation zone of the High Knob Massif. Granted all air flow trajectories comprise mean annual snowfall totals, but a significant amount of the annual tally is comprised of NW flow snow and even more is associated with air flow trajectories having westerly components.
A major, major problem in past decades were models that always tended to “model” heaviest snow toward the ECD, or Eastern Continental Divide, on NW Flow snow and most other flow trajectories ( the ”horseshoe” pattern that now shows up well in modeling around the Great Valley was not present during past decades ). Although model resolution has improved, it is still lacking in part because elevation remains a controlling factor + models can not understand or parameterize the initial lifting concept with still poor resolution of important complex terrain features ( ** ).
**This remains a major factor for the Cumberland Front more so than the Allegheny Front, since it becomes part of the Eastern Continental Divide at the latitude of central-northern West Virginia + there are many more NWS Cooperative stations at elevations above 3000 feet which are used as data inputs.
Although much terrain is above 3000 feet along the Cumberland Front, no stations are officially inputting any data into modeling now that the Black Mountain Cooperative has closed.
So initial lifting during NW Flow snowfall events continues to be under-estimated by both models and forecasters, with too much emphasis consistently placed upon what is the secondary lifting zone ( Blue Ridge ) in this type of flow.
I applaud Baker Perry & Charles Konrad for highlighting this fact years ago, yet it seemed to make little difference in the general forecast community to again exemplify the hole of disconnect that exists between operational forecasters in private, commercial and government sectors with those in the field doing on the ground research.
Even this above graphic is MUCH under-estimated since it incorporates no data from the snowiest mountain mass in Virginia where model errors on snowfall of all trajectories, but certainly on the NW Flow snowfall events, are much more than 30.5 cm listed for the Wise NWS Cooperative.
Wise tends to receive 40-60% less snow than upper elevations in the High Knob Massif, which is obvious to anyone in this area who may live or visit the area. Many residents live above 3000 feet on both the Wise & Scott County side of the high country. Leaving the portion in Scott County consistly out of most winter advisories is another problem that needs addressing ( it could be solved easily by joining that portion of Scott County north of the Clinch River with Wise County in winter weather settings such as NW flow ).
Moisture extraction along the initial lifting zone of the Cumberland-Allegheny Front on NW Flow snowfall means there is less moisture in a vertical atmospheric column to be precipitated out along the secondary lifting zone of the Blue Ridge, such that air has to be lifted to higher elevations in order to achieve as much snowfall. That is why it is nearly impossible, if not impossible, to find locations along the Blue Ridge where 75-100″+ of snowfall occurs annually at elevations as low as 3000 to 4200 feet ( *** ).
***Mount LeConte, at 6400 feet above mean sea level, at the summit level of the Great Smokies, on the windward side of the mountain range, has an annual snowfall average of around 100″ .
When Great Lake moisture transport into the initial lifting zone is vertically shallow in nature then it is impossible in many cases, regardless of elevation along the Blue Ridge, to achieve as much snowfall as on the Cumberland-Allegheny Front. If moisture transport is deeper; however, and also if orographic forcing is moderate-strong + upper dynamics are also favorable, then snow amounts reported at higher elevations along the Blue Ridge can match or occasionally exceed those at lower elevations along the Cumberland-Allegheny Front. This is especially true for peaks standing along the front of the Blue Ridge, such as Roan Mountain and Mount LeConte.
For forecast purposes, in particular, forecasters remain too limited and under-estimate the amount and coverage of NW flow snowfall along & west of the Cumberland Front as such events produce widespread accumulations ( # ). While this is of course partly due to a continued need for better terrain resolution by forecast models, it is also due to a fact that despite decades of forecasting and recorded climatology there never seems to be the needed adjustments.
#The widespread snow having enhancements with superposition of snow squalls and snow streaks developing in the 925 to 850 MB flow field to add to the widespread coverage. Leeward of initial lifting, coverage of accumulating snowfall is typically hit or miss and too often this hit-miss nature that is so common in downslope locations ( like the Great Valley ) is applied to the primary lifting zone in forecasts ( when only heavier local amounts should be stressed upon an otherwise widespread accumulation ).
The main focus from my perspective as both a researcher and teacher is this most important fact…the human brain remains the superior forecasting tool and is often forgotten with too much emphasis being placed upon computer model output, statistics, fancy graphics, and zone forecasts. Each forecaster should ideally make their own personal forecast from scratch, using raw model data and past climatology of analogous events, and if it then agrees with other forecast sources then that is great. In other words, do away with copy, slightly adjust, and paste!