Weather Headlines

*ALERT Continues For NW Flow Snow Into Tuesday Morning (December 3)

Update As Of 5:00 PM Monday ( 2 December 2019)

Steady light snow, and occasional heavier snow showers and local squalls, will continue with Great Lake moisture transport through Monday night before ending around mid-morning Tuesday.

Generally 1″ to 3″ of new snow is expected along the upslope side of the mountains into Tuesday AM, with higher amounts possible at highest elevations where blowing-drifting will also continue. Snowfall totals of less than 1″ are expected below 1200 feet (in lowest valleys along the upslope side of the mountains).

A general 2″ to 3″ of snow accumulation occurred above 3000 feet in the High Knob Massif by 8:30 AM Monday. Several more inches accumulated into the afternoon, with 4″-12″+ depths in blowing & drifting on High Knob and Eagle Knob by afternoon.

Locations below 1500 feet elevation had melting during the daylight hours Monday, but sticking will occur again Monday night into Tuesday morning at elevations above 1200-1500 feet on the upslope side of the mountains.

Previous Forecast & Discussion

A upper air disturbance, with very cold air aloft, will cause heavy snow, amid whiteout bursts, to develop Monday with low visibilities at times as temperatures continue to drop on developing WNW-NW upslope flow.

Past climatology and analog settings with these types of parameters have produced intense snow squalls in whiteout conditions. Those traveling, and otherwise expected to be outside should be prepared for periods of near zero visibility. The potential for local thundersnow exists.

Some snow squalls may develop a convective nature, with conditional symmetric instability (CSI) or slantwise columns of elongated clouds capable of supporting this despite low clouds tops (relative to typical convection) in the vertical.

Upslope snow showers will then continue into Tuesday.

Wind chills will also be a factor, especially at higher elevations, where single digits and 10s are expected Monday into early Tuesday, with WCF variations from 10s to lower 20s in more sheltered valleys at the lower elevations to around 0 degrees in gusts on highest peaks.

Final Snowfall Forecast

3″ to 5″ below 2500 feet
(locally higher amounts)

5″ to 7″ above 2500 feet
(locally higher amounts)

6″ to 10″+ above 3000 feet
**(bare ground to 1-2’+ drifts)

1/2″ to 3″ in downslope locations
(Clinch, Powell, Holston valleys)

Target snowfall of 5″ at 2500 feet (+/-) 1″ error potential, suggesting 4″ to 6″ possible at elevations of Norton-Wise with locally deeper depths developing where snow squalls are most intense and where blowing-drifting occurs.

**Blowing and drifting is expected to cause large snow depth differences at highest elevations in the High Knob Massif, with variations from near bare ground to 1-2+ feet in drifts. The potential for some roads, such as Route 237 at Davenport Gap, 238 at High Knob-Eagle Knob Gap, and State Route 619 in Little Mountain Gap, to become impassible will exist due to drifting.

Preliminary Snowfall Forecast

1″ to 3″ below 2500 feet
(locally higher amounts)

3″ to 6″ above 2500 feet
(locally higher amounts)

4″ to 8″ above 3000 feet
**(bare ground to 1-2’+ drifts)

1/2″ to 2″ in downslope locations
(Clinch, Powell, Holston valleys)

Target snowfall of 3″ at 2500 feet (+/-) 1″ error potential, suggesting 2″ to 4″ possible at elevations of Norton-Wise with locally deeper depths developing where snow squalls are most intense and where blowing-drifting occurs.

**Blowing and drifting is expected to cause large snow depth differences at highest elevations in the High Knob Massif, with variations from near bare ground to 1-2+ feet in drifts. The potential for some roads, such as Route 237 at Davenport Gap, 238 at High Knob-Eagle Knob Gap, and State Route 619 in Little Mountain Gap, to become impassible will exist due to drifting.

ALERT For Strong WNW-NW Winds At Middle To Upper Elevations, Above 2500 Feet, With Gusts of 30-40+ MPH Through Monday

Blowing and drifting snow will be a factor at upper elevations where strong WNW-NW winds will continue through Monday into Tuesday. Riming is also expected, with the extent of orographic feeder cloud formation ultimately acting to influence snowfall totals beneath and just downstream of them as snowflakes become rimed to increase total snow volume (*).

*This has been an observed and interesting part of my climatological research in the High Knob Massif, and has been documented in other orographic belts of the world. My predicted snowfall totals are higher above 3000 feet, in part, due to the expected riming of snowflakes falling through and being blown just downstream of orographic pilatus (cap or feeder) clouds forming on WNW-NW upslope flow. Riming of flakes acts to increase the amount of snow that accumulates on the ground over time, with rime drop from trees later adding additional moisture content to the ground snow cover.

A composite of more than 80 models, including all ensembles, is predicting snowfall variations from a Trace to 6″ at the Wise gridpoint. All these are based upon a snow density of 10:1 (snow to water ratio of 10″ of snow per 1.00″ of liquid equivalent).

My actual forecast is going above the mean of 3″ due to strong orographic forcing and the tapping of moisture from the Great Lakes, with lower snow densities (higher ratios) than indicated by models. In addition, a pocket of very cold air aloft will aid initial snowfall with blizzard-like bursts expected. Riming of snowflakes falling through orographic clouds at upper elevations will further enhance snowfall amounts above 3000 feet (**).

**Past climatology and analogs of similar settings support a more aggressive forecast than indicated by the mean of forecast models. While every event is different, and results vary, this can be a powerful tool for prediction of these types of winter events.

Past documented history of snowfall forecasts made since 2014 on the Appalachian Climate Center is verification of this fact, along with additional forecasts made going back to the early 1990s.

Caution For High Water Levels On Steep Creeks Draining The High Knob Massif Into Monday ( 2 December 2019 )

High water levels continue with ROARING creeks draining the High Knob Massif. Extreme caution is advised due to slick banks and high velocity flows.

Caution is also advised near the main-stem rivers. Although warnings are in effect for minor flooding, I think subterranean conduits within the High Knob Massif and along the Clinch and Powell river valleys will be able to take in more water than models predict given near to below average autumn precipitation.

Forecasting precise stream flows are very difficult in this karst area, with Wise, Scott and Lee counties collectively containing the highest cave density in Virginia. This is one of the greatest karst landscapes in North America, with an array of complex conduits at elevations varying from well over 3000 feet in the High Knob Massif to around 1000 feet on downstream valley floors (*).

*A karst landscape possesses a very dynamic, heterogeneous character with large and unknown subterranean features that are continuously changing through space and time, making hydrological predictions more difficult than within non-karstic terrain.

Previous Alerts and Discussions

*ALERT for ponding of water in low-lying locations and along roads, with the potential for rapid water level rises on streams during intervals of heavy rain and downpours.

An average of 3.00″ of rain had fallen across the High Knob Massif as of 4:00 AM on 1 December, with strong rises on creeks draining the upper elevations. Big Stony Creek was only 1/2 foot below flood stage as of 4 AM.

Please use extreme caution near creeks, and monitor water levels through Sunday morning.

*ALERT for strong SSW-WSW to W winds Saturday into Sunday (Nov 30 to Dec 1), beginning at upper elevations early on Saturday and expanding across the area Saturday Night into mid-AM Sunday.

A strong precipitation generated inversion, with cooler temperatures at low elevations versus high elevations, has kept stronger winds (15-30+ mph) along high ridges with calm conditions in lower elevation valleys. This scenario will change Saturday night and (especially) Sunday when vertical mixing will develop and become enhanced by turbulence.

Strongest winds are expected Sunday in most locations as mixing increases in a narrow dry slot, with efficient downward transfer of high momentum air. Strong winds will continue Monday into Tuesday at upper elevations, and in cross-barrier flow along and just lee of the Blue Ridge, in cold air advection on WNW-NW flow.

Reference 112619 Forecast for the previous event.

The next in a series of storm systems will spread rain, with a chance of thunderstorms, across the mountain region Saturday into early Sunday.

Reference Winter 2019-20 for a look ahead at main weather players.

There remains some disagreement in models regarding where bands of heaviest rains will fall, with the NAM and GEM (Canadian) groups being farther north while the GFS and ICON groups are farther south, as examples, with the ECMWF (European) members split among themselves.

As noted below, the latest run of the NAM Model group has trended southwest, more in line with the GFS-ICON models.

Predicted air flow vectors and orographics, combined with past climatology, suggests heavy rainfall will be likely in the mountain area, especially in favored orographic lifting zones along and northwest of the Cumberland-Allegheny Front.

The Cumberland Front typically functions as a weather change boundary, which becomes especially notable during winter when NW flow snowfall tends to be heaviest along and northwest of this boundary. It is otherwise focused along and just northwest of higher elevations of Clinch Mountain and the Blue Ridge (Mount Rogers-Whitetop southwest to the Smokies).

A dry slot of air will cause skies to break around mid-morning Sunday as the warm air advection rain shield lifts out of the region, with windy and relatively mild conditions before clouds increase as the comma-head of this large mid-latitude cyclone begins to wrap into the region to bring cold air advection and a redevelopment of rain and snow showers. A rapid change to snow at high elevations early Sunday evening will occur, with quickly dropping snow levels into middle elevations during the evening.

Cold air aloft generates vertical instability and while perturbation of low-levels with orographic lifting favors snow bursts in NW flow lifting zones, waves generated by the main mountain barriers, local hills, or just local instability, will be able to trigger snow burst development in typical downslope dominated locations.

Due to a pocket of very cold air aloft with an upper air disturbance, bursts of snow will not be restricted to just the typical NW flow orographic belts.

Reference Majestic Rime Opens November 2019

Weather Headlines

Rime formation continues on this Thanksgiving morning for highest elevations in the High Knob Massif (riming for the past 6-hours as of 10 AM). For visitors to the High Knob Lookout, expect wind chills in the single digits and 10s, in gusts, with temperatures in the 20s under a strong low-level inversion.

ALERT For HIGH Winds Continues Along The Blue Ridge In Cross-Barrier Flow

A strong low-level jet streak moving up along the western side of the Appalachians will cause high winds to develop into the predawn to morning hours of Wednesday (27 November).

850 MB Streamline Flow Field_USA

Wind gusts of 40 to 50+ mph will be likely, amid what looks to be a nearly classic high wind setting within a developing dry slot of a strong mid-latitude cyclone.

250 MB Streamline Flow Field_USA

It does not take a meteorologist to tell what directions will be favored if you, your family, or friends are flying across the USA during this Thanksgiving holiday.

Peak reported wind gusts along the Appalachians are likely to reach 60 to 100 mph, with the potential for places like Grandfather Mountain to top 100 mph during this event.

Hurricane force wind gusts will become possible on highest peaks, with hunters in the woods and visitors to places like the High Knob Lookout Tower urged to exercise extreme caution. Dense clouds and wind driven rains will also occur prior to the arrival of dry air within the cyclone’s dry slot.

Due to a unidirectional flow developing aloft, with 100 knot winds at 500 MB and 130+ knot winds at upper-level jet stream levels, I have extended the alert for high winds through Wednesday into the evening due to turbulent mixing enhanced by abundant afternoon sunshine.

The strongest low-level jet winds, blasting high peaks, will be during the 4 AM to 10 AM period, with strong wind gusts mixing downward into all elevations at times during the daylight and early-mid evening hours. High winds with downward transfer from upper jet stream levels and local channeling (such as through the gaps on Grandfather Mountain, Fancy Gap, and High Knob) and wave breaking will become a concern.

Turbulent mixing will begin to diminish after sunset along the western side of the Appalachians, but will continue along the eastern slopes of the mountain chain as a positive mountain torque is strengthened by a developing cross-barrier pressure gradient Wednesday night into early on Thanksgiving day.

Folks traveling north and east should be alert to strong cross-winds on portions of I-81 and I-77 (Fancy Gap), along with other roadways.

**Updated_Actual High Wind Reports

High Wind Reports_NWS And Research Stations
(27 November to 9:00 AM 28 November)

#Grandfather Mountain, NC: 97 MPH

(# 81.2 MPH sustained winds recorded at 4:39 AM 28 Nov)

1 NNE West Jefferson, NC: 71 MPH

2 NNE Snowshoe, WV: 67 MPH

5 E Canaan Heights, WV: 65 MPH

4 WNW Rugby, VA: 64 MPH

1 NE Bent Mountain, VA: 61 MPH

Jefferson, NC: 61 MPH

4 NW Wintergreen, VA: 60 MPH

Pikeville 13S, KY: 57 MPH
(Adjacent to Pine Mountain)

Burkes Garden, VA: 56 MPH

Boone, NC: 56 MPH

1 SE Marion, VA: 51 MPH

Lonesome Pine Airport: 40 MPH

Updated – The Next Snowfall Potential

A Recap Of Recent Wintry Events_Lingering Autumn Color

The potential for significant snow accumulations in the mountains, with snow squalls and bursts of heavy snow, on Great Lake connected NW upslope flow is increasing for the December 2-3 period.

Reference Winter 2019-20 For Major Players

A strong upper air wave, and cold pocket of air aloft, is being monitored for the enhancement of snowfall.

Stay tuned for later updates.

Reference Winter 2019-20 For Major Players

ALERT For Fog & Freezing Fog With Development Of A Deep Saturated Layer Sunday Night Into Monday Morning

Warm air advection centered around 850 MB will strengthen a low-level inversion which developed Sunday over the Great Valley and allow fog and freezing fog to expand in coverage.

A Recap Of Recent Wintry Events_Lingering Autumn Color

A rather interesting setting will feature lowering cloud bases in SW upslope areas of the High Knob Massif-Landform. As low-level temperatures cool ground fog development will become possible until eventually the two layers may be able to combine in a saturated zone through several thousand vertical feet of the atmosphere.

Freezing fog, with riming, is ongoing at upper elevations in the High Knob Massif and Black Mountain on SW flow. The evening-overnight potential will feature lowering of this over time in locations where SW flow rises.

Locations under a persistent cloud cover not subject to rising SW flow may be more protected from widespread fog formation, unless the cloud layer breaks to allow radiational cooling. A complicated setting that will require NOWcasting by forecasters as it evolves.

The 8:00 PM air temperature in Clintwood is 31 degrees but skies are clear. The potential for freezing fog exists but is less than in locations where SW air flow will be rising along the High Knob Landform and Massif (Clinch-Powell basins).

A Recap Of Recent Wintry Events_Lingering Color

The Winter Season Of 2019-20

The dawn of December will mark the beginning of Meteorological Winter 2019-20, so it is time to review some of the main players expected to impact the upcoming season (*).

*The following highlights some major forcing factors, but not nearly all the factors, and is given only as general guidance.

Beginning with the main climate system driver, the sun, Earth is currently within a deep solar minimum as 2019 is now poised to become one of the top years with respect to a lack of sunspots on the surface of the sun.

Track Sun Spot-Less Days On SpaceWeatherLive

*National Center for Atmospheric Research Staff (Eds). Last modified 20 Aug 2013. “The Climate Data Guide: QBO: Quasi-Biennial Oscillation.” Retrieved from https://climatedataguide.ucar.edu/climate-data/qbo-quasi-biennial-oscillation.

A -QBO phase in combination with a solar minimum enhances the potential for stratospheric warmings, with a major Southern Hemispheric warming having already been observed above Antarctica.

The above graphic shows the deviation of actual observed temperatures at 10 MB above the South Pole (black line) versus long-term climatological values (grey line). Warming began suddenly during late August-early September, fitting the name of Sudden Stratospheric Warming (SSW) which in this case was a major event.

This has been responsible, in part, for dryness and wild fires across Australia making current news headlines.

Initial warming above the North Pole during late autumn and early winter 2019-20 ended up being minor in nature, but with notable impacts on the hemispheric pattern.

Reference Early Winter 2019_High Knob Massif for more details.

A renewal of warming in the stratosphere is expected in early January, with time telling if this will be more significant with respect to impacting the Polar Vortex than the early season warming event.

Stratospheric warming is being driven by North Atlantic wave 1 forcing, with upward propagation and wave breaking (releasing mass, momentum, and energy) from the troposphere into the stratosphere in combination with upward wave activity flux (WAF) from Siberian snow cover as highlighted by Cohen to initiate the beginning of troposphere-stratosphere-troposphere coupling through coming weeks.

Judah Cohen highlights in his blog that snow cover extent during October was above average across Siberia, which favors stronger Siberian High Pressure and subsequent weakening of the polar vortex via upward wave activity flux (WAF) and feedback with tropospheric-stratospheric-tropospheric coupling leading to a negative Arctic Oscillation and colder than average conditions across mid-latitudes of the Northern Hemisphere.

Eurasian Snow Cover Variability And Links To Stratosphere-Troposphere Coupling

This is complicated and subject to variations depending upon the nature and positioning of forcing factors, both within and outside the arctic region and across the Northern Hemisphere.

As warming occurs, the polar vortex weakens and wind speeds decrease. During a Sudden Stratospheric Warming (SSW) event the direction shifts to easterly in direction. Warmings and SSW’s increase meridional flow across the Northern Hemisphere, enhancing transport of arctic air southward.

Although there is no official El Nino or La Nina running in the equatorial Pacific Ocean, the Southern Oscillation Index (SOI) has been consistently in decline as above average sea surface temperature (SST) anomalies are concentrated mostly in the central Pacific Ocean (versus eastern Pacific in classic +ENSO).

A rise in the daily SOI occurred through early December with a lag time correlated to a milder pattern developing in the eastern USA during mid-late December 2019.

A renewed and stronger mid-late December drop in the SOI may be signaling the return of a colder pattern in the eastern USA by early January 2020.

This is a Modoki El Nino (+ENSO) signal which has, from a climatological perspective, favored colder than average conditions in eastern North America and the eastern USA.

A positive Indian Ocean Dipole (+IOD) phase acts to enhance any positive ENSO that may be present during the same time.

The PNA has mostly been in its positive phase (+PNA) during November, which has been anomalously cold, following the mainly -PNA phase of October 2019 that featured much above average temperatures.

The most recent PNA trend has been negative and associated with milder conditions in the eastern USA. This trend is predicted to change back to positive as January 2020 approaches.

Warm sea surface temperatures, relative to average, within the Gulf of Alaska favors a positive PNA oscillation pattern and downstream troughing across the eastern USA, but the positioning and extent of western Pacific ridging is critical.

The December 1-19 pattern has been split between colder than average and near average to milder than average conditions across the southeastern USA.

The general December 1-19 pattern featured near to a little above average temperatures across much of the continental USA.

Blocking near the Aleutians and across Greenland was a persistent feature through Summer 2019 to the present, which contributed to major melting of the Greenland ice sheet (continental glacier).

The continuation of warm sea surface temperatures around Greenland would favor high latitude blocking to continue over this region of the North Atlantic.

Snow and ice extent across North America and Eurasia are near decadal averages, which is now ready for southward expansion of a more long-lived nature. Expansion across the northern USA will aid southward movement through the end of 2019, with initially wet and stormy conditions (featuring mainly rain) in the south.

If positive snow cover anomalies develop, as models currently predict, across eastern and southeastern Canada into December this will be a strong signal for later wintry conditions across the eastern USA and Appalachians versus if the main positive snow cover anomalies were to develop across western Canada.

Feedback associated with positive snow cover anomalies force a natural southward progression of the baroclinic zone (and main storm track) over time, since storm systems feed upon thermal contrasts developing across snow cover-bare ground gradients.

The Bottom Line

Many factors currently favor a colder than average winter season during 2019-20, with stormy conditions across much of the nation (especially in the Great Lakes to Appalachians corridor of the eastern-northeastern USA).

The potential for severe winter periods are likely given highlighted factors, but this will depend upon how the forcing from each of these different teleconnections (Modoki +ENSO, -QBO, SST Anomalies, Polar Vortex changes, snow cover, and more not highlighted here) interact at any given time during coming weeks to dictate the magnitude and extent of these periods.

Long-term forecasts remain elusive given complex feedbacks within and between components of the climate system, with short-term events in both space and time acting to alter conditions immediately that then can force subsequent changes which may skew a month or season away from a prediction made prior to development of the short-term event(s).

This is an evolving situation, as always during the Holiday season, so check back for later updates as conditions change across the Northern Hemisphere.

Weather Headlines

ALERT For A Rapid Temperature Drop Saturday Evening Into Sunday Morning With Rain Showers Changing To Snow Showers Amid Strong SW To NW Winds

Local downpours along a strong cold front will cause a gusty wind shift from SW-WSW to WNW-NW winds and rapidly dropping temperatures this evening into the overnight hours of Sunday morning.

Rain changing to snow showers will redevelop during the evening into the overnight as a upper-level disturbance passes across the southern-central Appalachians. Heaviest snow amounts with this vorticity maximum will occur to the north in West Virginia, especially in the central-northern highlands of WV where Great Lake moisture will enhance amounts, but some sticking snow is expected in higher elevations of the southern Appalachians.

Expect snowfall accumulations of less than 1″ below 3000 feet, with 1-2″ possible above 3000 feet, into the predawn hours of Sunday (24 November). Little to no accumulation is expected below 1800 feet.

The worst conditions are expected to develop at elevations above 3000 feet, with temperatures at highest elevations dropping into the low-mid 20s by Sunday morning. Wind chill factors will plunge into the single digits and 10s at upper elevations, with upper 10s & 20s chills at middle-lower elevations.

Some rime formation is expected above 3000 to 3500 feet into Sunday morning in the High Knob Massif and Black Mountain.

Former Alert

*ALERT For A Period Of Dense Fog Friday Evening As Cloud Bases Drop Into Middle Elevations Along And North Of The Tennessee Valley Divide And High Knob Massif

*While fog will be mainly present at upper elevations, above 3000-3300 feet, into early Sunday amid orographic capping pilatus (feeder clouds), a period of dense fog will also be possible into middle elevations (below 3000 feet) as cloud bases lower for a period Friday night on northerly upslope flow along and north of the High Knob Massif.

The longevity of any fog forming in middle to lower elevations Friday night into early Saturday will be dependent upon a developing inversion, and if it may be able to maintain fog near the surface in places where fog develops.

A Recap Of Recent Wintry Events_Lingering Color

A stormy and much wetter pattern is now looking to develop through the last week of November into the first week of December 2019.

Ensemble members show locally lesser and higher amounts, with much higher amounts on some individual members. This pattern has the potential to refill water supply reservoirs, serving the High Knob Massif area, during the next several weeks.

The GFS Model is now coming into alignment with the European Model group in predicting a series of storm systems, with significant precipitation, to impact the mountain region and Tennessee Valley during the final week of November and the first week of December.

While the majority of this precipitation is currently expected to be in liquid form, dual blocks over the Northern Pacific and North Atlantic (southern Greenland) will have to be monitored for the potential of lower heights and colder air that could contribute to additional frozen types at times despite a warmer, mean flow pattern.

A southwesterly flow regime, in the mean, across the southern-central Appalachians and Tennessee Valley will transport significant amounts of moisture from the Pacific Ocean and Gulf of Mexico.

Orographic forcing, as recently observed, will be a notable player as the orographic forcing season gets underway with vigor through coming weeks. Since precipitation recording began at Big Cherry Dam in 2007-08, in the High Knob Massif, December has been the wettest month of the year.

This has been associated with the annual increase in orographic forcing that develops during the Thanksgiving-Christmas Holiday period, when storm systems feeding upon thermal differences develop pressure gradients that drive strong winds into the mountains with development of positive-negative forcing couplets and mountain torques.

The mountains are not static, but push back against the atmosphere to generate torques that influence the magnitude and spatial distribution of precipitation and temperatures, such that orographic forcing is a vector phenomenon endemic to mountainous and hilly landscapes across planet Earth. They extend their influence and communicate to other portions of the atmosphere through waves that develop and ripple outward from their orographic forcing zones with transport of mass, energy, and momentum to places removed (sometimes very far removed) from their forcing.

The Winter Season Of 2019-20

The dawn of December will mark the beginning of Meteorological Winter 2019-20, so it is time to review some of the main players expected to impact the upcoming season (*).

*The following highlights some major forcing factors, but not nearly all the factors, and is given only as general guidance.

Beginning with the main climate system driver, the sun, Earth is currently within a deep solar minimum as 2019 is now poised to become one of the top years with respect to a lack of sunspots on the surface of the sun.

*National Center for Atmospheric Research Staff (Eds). Last modified 20 Aug 2013. “The Climate Data Guide: QBO: Quasi-Biennial Oscillation.” Retrieved from https://climatedataguide.ucar.edu/climate-data/qbo-quasi-biennial-oscillation.

A -QBO phase in combination with a solar minimum enhances the potential for stratospheric warmings, with a major Southern Hemispheric warming having already been observed above Antarctica.

The above graphic shows the deviation of actual observed temperatures at 10 MB above the South Pole (black line) versus long-term climatological values (grey line). Warming began suddenly during late August-early September, fitting the name of Sudden Stratospheric Warming (SSW) which in this case was a major event.

This has been responsible, in part, for dryness and wild fires across Australia making current news headlines.

A strong stratospheric warming, with temperature increases of up to 80+ degrees Fahrenheit at 10 MB above the Northern Hemisphere, is being predicted by the GFS Model group heading into the first week of December 2019.

Stratospheric warming is being driven by North Atlantic wave 1 forcing, with upward propagation and wave breaking (releasing mass, momentum, and energy) from the troposphere into the stratosphere in combination with upward wave activity flux (WAF) from Siberian snow cover as highlighted by Cohen to initiate the beginning of troposphere-stratosphere-troposphere coupling through coming weeks.

Judah Cohen highlights in his blog that snow cover extent during October was above average across Siberia, which favors stronger Siberian High Pressure and subsequent weakening of the polar vortex via upward wave activity flux (WAF) and feedback with tropospheric-stratospheric-tropospheric coupling leading to a negative Arctic Oscillation and colder than average conditions across mid-latitudes of the Northern Hemisphere.

Eurasian Snow Cover Variability And Links To Stratosphere-Troposphere Coupling

This is complicated and subject to variations depending upon the nature and positioning of forcing factors, both within and outside the arctic region and across the Northern Hemisphere.

The Polar Vortex is now predicted to weaken, with magnitude and extent of this yet to be determined along with resulting impacts for any given region.

As warming occurs, the polar vortex weakens and wind speeds decrease. During a Sudden Stratospheric Warming (SSW) event the direction shifts to easterly in direction. Warmings and SSW’s increase meridional flow across the Northern Hemisphere, enhancing transport of arctic air southward.

Although there is no official El Nino or La Nina running in the equatorial Pacific Ocean, the Southern Oscillation Index (SOI) has been consistently in decline as above average sea surface temperature (SST) anomalies are concentrated mostly in the central Pacific Ocean (versus eastern Pacific in classic +ENSO).

This is a Modoki El Nino (+ENSO) signal which has, from a climatological perspective, favored colder than average conditions in eastern North America and the eastern USA.

A positive Indian Ocean Dipole (+IOD) phase acts to enhance any positive ENSO that may be present during the same time.

The PNA has mostly been in its positive phase (+PNA) during November, which has been anomalously cold, following the mainly -PNA phase of October 2019 that featured much above average temperatures.

Warm sea surface temperatures, relative to average, within the Gulf of Alaska favors a positive PNA oscillation pattern and downstream troughing across the eastern USA, but the positioning and extent of western Pacific ridging is critical.

Blocking near the Aleutians and across Greenland was a persistent feature through Summer 2019 to the present, which contributed to major melting of the Greenland ice sheet (continental glacier).

The continuation of warm sea surface temperatures around Greenland would favor high latitude blocking to continue over this region of the North Atlantic.

Snow and ice extent across North America and Eurasia are near decadal averages, which is now ready for southward expansion of a more long-lived nature. Expansion across the northern USA will aid southward movement through the end of 2019, with initially wet and stormy conditions (featuring mainly rain) in the south.

If positive snow cover anomalies develop, as models currently predict, across eastern and southeastern Canada into December this will be a strong signal for later wintry conditions across the eastern USA and Appalachians versus if the main positive snow cover anomalies were to develop across western Canada.

Feedback associated with positive snow cover anomalies force a natural southward progression of the baroclinic zone (and main storm track) over time, since storm systems feed upon thermal contrasts developing across snow cover-bare ground gradients.

The Bottom Line

Many factors currently favor a colder than average winter season during 2019-20, with stormy conditions across much of the nation (especially in the Great Lakes to Appalachians corridor of the eastern-northeastern USA).

The potential for severe winter periods are likely given highlighted factors, but this will depend upon how the forcing from each of these different teleconnections (Modoki +ENSO, -QBO, SST Anomalies, Polar Vortex changes, snow cover, and more not highlighted here) interact at any given time during coming weeks to dictate the magnitude and extent of these periods.

Long-term forecasts remain elusive given complex feedbacks within and between components of the climate system, with short-term events in both space and time acting to alter conditions immediately that then can force subsequent changes which may skew a month or season away from a prediction made prior to development of the short-term event(s).

This is an evolving situation, as always during the Holiday season, so check back for later updates as conditions change across the Northern Hemisphere.

ALERT For Snow & Hazardous Conditions Developing During The Predawn-Sunrise Period Of Tuesday (12 November)

A change from rain to heavy snow is expected during the predawn hours of Tuesday, with plunging air temperatures and a strong wind shift to NW-N upslope flow for locations along and north of the High Knob Massif and Tennessee Valley Divide. A transition to snow will occur across the mountain area, but heaviest snow amounts and worst conditions are anticipated in the above noted zone.

Widespread hazardous road conditions are expected to develop during the predawn to post-sunrise period of Tuesday. This will NOT be a slick spot type of scenario, but a setting that produces widespread snow covered roadways (especially secondary roads). Caution is advised.

A combination of low-level convergence and upper-level divergence into the right-rear quadrant of a strong 200-300 MB jetstreak will combine with orographic lift to generate heavy snowfall Tuesday morning. The potential exists for higher snowfall amounts than I am forecasting, with a notable model trend of increasing amounts.

While the greatest snow depths will tend to be on above ground objects, a rapid temperature drop and a long stretch of cold November nights will aid sticking of snowfall given rates of fall are expected to become intense as orographics and dynamics phase Tuesday morning.

Final Snowfall Forecast

A general 2″ to 4″ of snow are expected along and north of the High Knob Massif and Tennessee Valley Divide, with locally higher amounts possible above 3000-3500 feet in the High Knob Massif

*Target Snowfall: 3.0″ (+/-) 1.0″ Error Potential for Norton, Wise, Clintwood, and Nora 4 SSE, suggesting 2″ to 4″ snowfall potential during the period from 2:00 AM to 2:00 PM Tuesday (Locally higher amounts)

*The average of approximately 80 forecast models, when including all 72 members of the European and GFS ensembles, forecasts a mean of 3.2″ at the Wise gridpoint with a spread from 1.7″ to 5.5″ being given across all members.

Updated_11:00 PM Monday: A Winter Weather Advisory is now in effect for the Tri-Cities through Tuesday AM, which I think is an excellent decision by the MRX National Weather Service Forecast Office given expected snowfall rates, timing, and dropping temperatures.

ALERT For Bitterly Cold Air Temperatures And Wind Chill Tuesday With Record Cold Expected Wednesday AM (13 November)

Temperatures are expected to drop into the 0 to 10 (F) degree range into Wednesday morning, with potential for sub-zero minimums in colder mountain valleys if winds calm and skies can clear over snow cover.

Major Arctic Blast

A major blast of arctic air, which has now been long advertised by models, especially the European Group, will strike the Appalachians early next week with bitter air temperatures-wind chills and accumulating snow.

The current cold can be used as a guide, with temperatures early next week expected to be 10-15 degrees colder than today and tonight (November 8-9). Temperatures today (Nov 8) varied from mid-upper 10s to mid-upper 20s on High Knob, and from the low-mid 20s to low-mid 30s in Norton-Wise. Wind chills, however, will make conditions feel much colder next week.

The coldest 24-hour period, from 7 AM Tuesday to 7 AM Wednesday, of November 12-13, will feature the coldest air mass in the entire Northern Hemisphere, relative to climatological means, over the Appalachians from the Cumberland Mountains northeast to the Alleghanies.

Air temperatures are expected to drop to around 0 degrees at the summit level of the High Knob Massif, with readings plunging toward 10 degrees in Norton-Wise.

Snow cover could potentially make temps even colder, and this will need to be updated later. Irregardless of snowfall, wind chill values will be brutal for this time of year.

While there remains time for some adjustment in the magnitude of this cold blast, a strong arctic high and cross-polar flow will no doubt make it plenty bitter enough irregardless of exact values which are ultimately obtained.

Accumulating snow is expected to begin prior to sunrise Tuesday, November 12, with hazardous conditions likely to develop with falling temperatures and wet road surfaces.

Updated Late Week Potential

Majestic Rime Opens November 2019_High Knob Massif

A non-phasing scenario has been recently shown by forecast models of the European group, but a late week storm still looks to develop. At this time it appears to be just a little too far off toward the south and southeast to impact the Appalachians, but not the Atlantic Coast.

This, of course, remains outward into time so changes remain likely and potential for a storm impacting the Appalachians can not yet be written off as dead.

Stay tuned for later updates.