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.

ALERT For Lowering Cloud Bases And Dense Fog Development During Monday Afternoon Into Tuesday In Locations Along And North Of The High Knob Massif & Tennessee Valley Divide (At Elevations Above 2000-2500 feet)

The first strong cold front of the autumn season will lower cloud bases and spread rain across the mountain landscape Monday into Tuesday, with temperatures falling through the 50s Monday afternoon into Tuesday in locations along and north of the High Knob Massif and Tennessee Valley Divide.

Surface Wind Streamline Trajectories

Update_Monday Evening_7 October 2019

Air flowing south across the Ohio River and upward into the Cumberland Overthrust Block is generating low cloud bases and very dense fog, with near zero visibility at times, across large areas of Wise & Dickenson counties. Please slow down and use extreme caution.

Dense fog will develop on northerly upslope flow, with dropping cloud bases into middle elevations (below 3000 feet) by later Monday into Tuesday. Caution is advised.

Mountain Area Forecast (Monday-Tuesday)

Overnight Into Monday Morning

Cloudy. Chance of a shower or drizzle. Gusty SSE-SSW winds 5-15 mph, with higher gusts, at elevations below 2700 feet. Winds S-SE at 10-20 mph, with higher gusts, above 2700 feet. Low clouds with dense fog at highest elevations. Temperatures varying from mid-upper 50s to the lower-middle 60s (coolest highest elevations).

Monday Afternoon

Rain developing. Chance of thunder and local downpours. Turning much cooler. Lowering cloud bases with dense fog development from upper elevations into the middle elevations by late afternoon. Scattered fog in other locations. Winds shifting NNW-N at 5-15 mph with higher gusts. Temperatures dropping into the 50s by mid-late afternoon from Norton-Wise north-northeast, warmer south of the High Knob Massif.

Monday Night Into Tuesday Morning

Periods of light rain and drizzle. Cool. Dense fog at mid-upper elevations. Winds N-NE at 5-15 mph with higher gusts. Temperatures varying from mid-upper 40s to the low-mid 50s, coolest highest elevations, milder toward the south into the Great Valley.

Live Interactive Doppler Radar

Tuesday Morning Through The Afternoon

Dense fog through the day at upper elevations, with cloud bases slowly lifting or partially lifting off middle elevations. Chance of light rain and drizzle. Winds N-NE at 5-15 mph with higher gusts, especially along mountain ridges. Temperatures mainly in the 50s to around 60 degrees (40s to low 50s at highest elevations), warmer across river valleys of the Clinch, Powell, and Holston.

Mainly Dry Pattern With Dorian Subsidence

Dorian is approaching the theoretical upper limit of its wind speed based upon sea surface temperatures, despite a barometric pressure higher than would be expected. This is partly due to its compact, small size and the conservation of angular momentum. As sea surface temperatures continue to warm with changing climate, the potential wind speed of such storms will tend to increase over time (at least, theoretical limits of wind speed will rise).

Surface Streamline Flow Field

Although much more complicated, of course, since temperature differences force pressure differences that generate pressure gradients which drive the wind, the atmospheric area in which Dorian will tend to move can be seen on this extracted example (above) from a point in space and time. The best chance, as has been forecast from the MEAN of the 51-member ensemble group of the European Model, of a mainland landfall will be along the coastline of North Carolina. Note this would be an official landfall, as due to expansion of the wind field over time the impacts will be felt all along the coast even without official landfall.

500 MB Streamline Flow Field

If you have been following this in previous days you observed a trough in the flow field in advance of Dorian, stretched along and just east of the Atlantic Coastline (the suggested pathway for Dorian to follow).

As the storm circulation of Dorian lifts northward the flow field of the storm overwhelms this visible trough, although, an area of lower pressure often remains (actually develops) in advance of low pressure systems (relative to the surrounding atmosphere). Such changes, and associated height falls, along with axes of theta-e (representing available potential energy) are used in combination with many other parameters to help forecast future storm movements (both tropical cyclones as well as mid-latitude cyclones). Improved forecasting over time being largely driven by vast increases in computing power, via supercomputers, and a vast increase in the amount of data available to be put into models. Due to the non-linear nature of fluxes and feedbacks between interconnected components of the climate system, the challenge of accurately forecasting these events remains significant, to say the least, and no one should get overly confident that the next big storm will also follow the predicted pathway as closely as Dorian up to this point (the storm event is NOT over by a long-shot at the time of this writing for the Carolinas, on 5 September 2019 at 0730z, with many long hours remaining).

This is merely for educational purposes, as this pathway is NOT set in stone and only small westward shifts could greatly change impacts along the Atlantic Coast. It should also be noted that the future storm track may come into alignment with the Gulfstream Current, such that future intensity changes become more uncertain.

Gulf of Mexico-Atlantic Gulfstream Current

Updated_6 PM_4 September 2019: Observe that a recent increase in the strength of Dorian is occurring as the storm moves more in alignment with the high energy content of the Gulf -Stream Current, as I suggested a couple days ago.

Although some local showers and downpours in thunderstorms will be possible Monday afternoon, and possibly on other days, mainly dry conditions are currently expected across most of the mountain area for most of the time through this week as potent Hurricane Dorian moves along the Atlantic Coast, with increasing subsidence around its periphery. Building heights and warmth is expected in Dorian’s wake by this weekend into next week, which will tend to prolong the general dryness and promote late season heat across the Tennessee Valley and southern Appalachians.

The NAM Model suggests some localized, hit-miss activity will be possible, especially during the next few days ahead of main subsidence (sinking air) influences of Dorian.

A cold front and initial indirect influences from Dorian will turn low-level winds northerly, with significantly cooler air, Thursday into Friday, especially in locations along and north-northwest of the Cumberland-Allegheny Front where adiabatic upslope flow cooling will be enhanced. As Dorian pulls away, subsidence will begin to rule the vertical motion field by this weekend into next week as discussed later in this section.

Dorian’s impressive satellite presentation continued into the early hours of Labor Day, with only limited signs of change.

A hurricane is a thermal heat-engine with strengthening, when all else is neglected, directly proportional to the rate of energy transfer across the air-sea surface interface. Surface and sub-surface ocean temperatures are therefore critical to development via strengthening of the latent heat flux and a vertical transfer of energy stored in the ocean to the atmosphere. This creates formation of a temperature gradient which supports a pressure gradient that drives horizontal and vertical air flow into and out of the system. Maximums of theta-e and vorticity become subsequently concentrated within the eyewall of tropical cyclones able to utilize available energy to reach hurricane status (wind speeds of 74 mph or higher).

At just past midnight, September 2, the position of Dorian was nearly identical to where the mean of the 51-member European Ensembles predicted it to be from the 1200z (8 AM) model run of September 1. The real test, however, will come on this Labor Day when Dorian is predicted to slow down and “briefly” stall by Monday afternoon before making a NW turn.

Water vapor imagery (below) reveals strongly sinking air within the eye and a beautiful, feathery array of gravity waves associated with anticyclonic outflow aloft. Gravity waves are also generated by mountains (like the High Knob Massif) and function to transfer mass, energy and momentum through space and time (spacetime). Like ocean waves rolling into a beach, feeling the frictional drag of the bottom, they eventually break and dissipate, fully releasing their transported mass, energy and momentum to the surrounding atmosphere.

Interactive Doppler Radar

UPDATE_The new Labor Day morning update of the European Model remains very consistent with above noted trends, with a slow wobble ongoing before a turn and increase in forward speed develops into Tuesday (September 3). The new track forecast keeps the eyewall of Dorian offshore and close to or barely crossing the Outer Banks of North Carolina.

NOTE: I am not allowed to show the detailed 51-member European Model (ECMWF) ensemble model cluster, or the individual member solutions, without a license from the European Center for Medium Range Weather Forecasting. The cluster below includes many different models generated by different agencies.

Late Season HEAT Builds Into Next Week

Late Summer 2019_High Knob Massif

A short-lived push of cooler air during September 5-6 will give way to warming conditions, at least by day, during this weekend through much of next week as upper air ridging develops across the mountain region.

It is not surprising that the core of highest upper-level heights into this weekend and next week will be located over the same region where heights will be lowest this week with the movement of hurricane Dorian, as a huge amount of air being ejected aloft in gravity wave filled upper-level outflow will be sinking in its wake.

Recall the atmosphere expands vertically as it warms, such that the height of any given level rises. A vertical column from the surface to the top of the troposphere expands such that a 500 MB forecast chart can be used to predict mean temperature in addition to other parameters. The 591 decameter value on the above forecast chart is equivalent to 19,378 feet (meaning that the 500 MB level will expand vertically to reside approximately 3.7 miles above the smoothed surface). That is well above the climatological mean height of the 500 MB surface for this time in September, thus forming a positive height anomaly over the SE USA. Observe that a stronger (+) height anomaly at 500 MB is forecast over NW Canada, where the actual 500 MB height will be lower than over the SE USA but more anomalous relative to climatology given the typically colder, more contracted vertical nature of the atmosphere above the Northwestern Territories at this time of year.

Subsidence (sinking air aloft) in the wake of Dorian will act to enhance a synoptic-scale pattern supportive of late season heat next week as the hurricane moves across the North Atlantic.

Anomalous to record level heat for September will be building over much of the southern-central portions of the USA, especially to the east of the Rockies centered across the middle Mississippi, Tennessee-Ohio valleys and southern Appalachians.

Heavy Rainfall Potential In Showers & Downpours In Thunderstorms During Thursday And Friday (August 22-23) Locally Strong Storms Possible

Late Summer 2019_High Knob Massif

An enhanced surge of humid, moisture laden air will interact with an approaching cold front and upper air wave to trigger showers and downpours in thunderstorms during Thursday into Friday. Folks living and driving along streams and within poor drainage, low-lying locations should remain alert for the potential of rapid water level rises and ponding of water.

Gaps within the coverage of heavy rains is the model way of predicting hit-miss action for heaviest amounts, although, a tendency for heaviest rains along & west of the Cumberland Mountains has been a local trend.

Totals between 1.87″ and 2.13″ have, for example, been forecast at the Wise gridpoint during the past two model runs. The latest ECMWF (European) Model is similar to the NAM. Models struggle with timing and amounts associated with convection, such that these graphics and model runs should only be used as a signal for heavy rainfall potential.

Stay tuned to NOAA Weather Radio and your favorite media sources for possible watches and or warnings that may be needed.

Full Screen Interactive Doppler Radar

Although a shower or downpour in a thunderstorm can not be ruled out during the next few days, the main threat for heavy to excessive rainfall will be most likely to return by the middle to end of this week (August 7-9) with a cold frontal boundary.

Greenland Blocking will continue to be a notable feature of Northern Hemisphere weather though the upcoming week to ten days, with general troughing across the eastern United States. Temperatures will be near to somewhat above average. Small chances for showers and thunderstorms early this week will increase during mid-late week when the potential for locally heavy to excessive rainfall amounts will return to the mountain landscape.

A super-wet summer in the high country of the High Knob Massif has generated more than 22.00″ of rainfall during the June 1 to August 2 period of 2019 (22.60″ at Big Cherry Dam).

Wet Summer of 2019_High Knob Massif

Monthly Total Precipitation
Big Cherry Lake Dam
(Elevation 3139 feet)

January
6.14″

February
12.50″

March
5.93″

April
6.64″

May
6.75″

June
10.68″

July
10.77″

August 1-2
1.15″

Summer 2019
(Jun 1-Aug 2)
22.60″

*2019 Total: 60.56″ (M)
(January 1 to August 2 Period)

12-Month Total: 91.85″ (M)

(M): Some missing moisture in undercatch and frozen precipitation, with partial corrections applied for the 24.4 meter (80 feet) tall dam structure where rain gauges are located.

*ALERT For Gully Washing Hit Or Miss Showers And Torrential Downpours In Thunderstorms

Light winds aloft and abundant low-level moisture will continue to support torrential rain producing showers & thunderstorms through coming days. Heavy to excessive rainfall will remain possible with ponding of water and flooding of low-lying, poor-drainage areas, as well as creeks in locations receiving heaviest rain amounts.

Local rainfall amounts of 3.00″ to 4.00″+ where experienced in portions of Wise and extreme northern Scott & Lee counties during the July 30-31 period. Additional heavy rain over these locations would pose an enhanced risk of flash flooding. Please monitor NOAA weather radio and your favorite media sources for possible advisories and warnings which may be needed during coming days.

Mountain Area Weather Headlines

A super-wet summer in the high country of the High Knob Massif has generated more than 20.00″ of rainfall during the June 1 to July 31 period (during 66% of the summer season, or now past the half-way point of Meteorological Summer 2019).

Brilliant sun rays strike gushing whitewater tumbling out of Big Cherry Lake basin during morning hours of July 24. Vapor from the water was visibly rising back upward into the air, during a summer season in which the surface energy budget has been dominated by latent heat flux to an extent even more than typical of this wettest terrain in Virginia.

Wet Summer 2019_High Knob Massif

Big Cherry Lake Dam
(Elevation 3139 feet)

January
6.14″

February
12.50″

March
5.93″

April
6.64″

May
6.75″

June
10.68″

July
10.77″

*2019 Total: 59.41″ (M)
(January 1 to July 31 Period)

12-Month Total: 91.45″ (M)

(M): Some missing moisture in undercatch and frozen precipitation, with partial corrections applied for the 24.4 meter (80 feet) tall dam structure where rain gauges are located.

*Big Cherry Lake basin is the most productive water supply basin per unit area within the Old Dominion of Virginia. Anyone who does not believe this is free to find another basin with higher precipitation totals over a period of years to decades that contains a water supply producing lake watershed.

Looking Ahead To Beginning Of August

Near to well below normal 500 MB heights are being predicted during the first week of August as general upper air troughing occurs over the northeastern USA, downstream of a sprawling upper-level high pressure dome centered over the heartland.

This should generally support an increase in showers and thunderstorms, with near to below average air temps along the Cumberland-Allegheny Front where air will be rising in the mean on western component flow (SW-W-NW) during this time period.

While this pattern will generally support near to below average temperatures across the region, the greatest anomalies will tend to occur where air is also rising in the mean with more condensation, clouds and precipitation.

Although not quite as pertinent during the summer season, both the European and GFS model ensemble means signal this pattern with their teleconnections.

A notable -NAO (negative phase of the North Atlantic Oscillation) will be joined by a developing positive phase of the Pacific North American oscillation (+PNA) through the first week of August.

The Eastern Pacific Oscillation (EPO) is also now showing a negative phase developing during the first week of August 2019, adding more confidence to the forecast for eastern USA upper air troughing.

During winter these are cold teleconnection signals for eastern North America, while during summer they suggest near to below average temperatures which are more tolerable (of course).

Greenland Blocking, a persistent summer feature during 2019, will again be a prominent aspect of the Northern Hemisphere flow field into early August.

After some down time, the Appalachian Climate Center will be back up and running during coming days and months.

Meanwhile, enjoy an autumn preview as a beautiful air mass arrives courtesy of our friends at high latitudes.

700 MB Flow Field

Severe Weather Threat Continues Through Monday (June 24)

An Enhanced Threat Of Severe Thunderstorm Development Has Been Issued Along With A Severe Thunderstorm Watch

Valid 241630Z – 251200Z

…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
OF THE CENTRAL APPALACHIANS…

…SUMMARY…
Scattered strong to severe storms capable of damaging winds will
affect the central/southern Appalachians and Ohio Valley today.
Other more isolated severe activity is possible today over northern
Illinois/southern Wisconsin and vicinity, and over
west-central/southwest Texas.

…Central/Southern Appalachians…
Morning satellite and radar imagery show a well-defined remnant MCV
over southern KY. This trough is embedded with a larger upper
trough rotating across the OH/TN valleys. The air mass ahead of the
feature is heating rapidly and will become very unstable by
mid-afternoon. Strengthening midlevel winds, coupled with strong
instability and affects of the MCV will pose a more substantial risk
of bowing thunderstorm structures capable of damaging wind gusts. A few supercells cannot be ruled out, along with a risk of isolated
tornadoes. Therefore have upgraded much of WV and vicinity to an
ENH risk and 30% severe wind probabilities.

1249 AM CDT Mon Jun 24 2019

Valid 241200Z – 251200Z

…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE GREAT LAKES SOUTHWARD INTO THE SOUTHERN APPALACHIANS AND IN PARTS OF THE SOUTHERN PLAINS…

…SUMMARY…
Scattered storms, some severe with hail or wind, are expected today the southern Great Lakes southward across the Ohio Valley into the Southern Appalachian Mountains. Other severe storms may occur across parts of the southern Plains.

…Ohio Valley/Southern and Central Appalachians…
An upper-level trough will move eastward across the Mississippi
Valley today as southwest mid-level flow remains over east-central
U.S. At the surface, a cold front will advance eastward into the
Ohio and Tennessee Valleys as a corridor of maximized low-level
moisture sets up ahead of the front. Surface dewpoints in the upper 60s F should result in moderate instability by midday across much of the moist sector. As surface temperatures warm and low-level convergence increases along the front, scattered convection is
forecast to initiate along and ahead of the front. Linear MCS
development will be possible as storms increase in coverage and move northeastward across the moist sector during the afternoon. RAP forecast soundings ahead of the front by 21Z from northern Kentucky southward into the southern Appalachian Mountains show MLCAPE values from 1000 to 2000 J/kg with steep low-level lapse rates. This along about 30 kt of 0-6 km shear should be favorable for isolated damaging wind gusts. Hail will also be possible with the stronger cells embedded in the any line that becomes established.

SPC authored by Broyles/Cook…06/24/2019

An enhanced threat for W-NW flow Mesoscale Convective Systems (MCS) is being monitored, with the potential for widespread wind damage generating Derecho formation. In addition, supercells and an enhanced flash flood risk will be a significant concern. While the exact track is yet to be determined for these systems, confidence for their development is high, and locations across the Ohio and Tennessee valleys into the Appalachians will be at risk.

While the above graphic does not look ominous yet, I expect significant upgrades to be made by the SPC during the next 24 to 48 hours as this setting gets closer in time.

An enhanced flash flood risk will remain a concern given so much rainfall already observed during June 1-20 and in 2019 which, like 2018, has been another very wet year.

Superintendent Andrew Greear, of the City of Norton Water Plant, reported 7.45″ of June rainfall up to 9:00 AM Thursday, June 20, which brought the 2019 tally to 40.28″ for the city (official NWS rain gauge total).

June rainfall totals of 8.00″ to 9.00″, with locally higher amounts, have been common in upper elevations of the High Knob Massif where 2019 precipitation tallies have reached 45.00″ to 50.00″ .

Locally higher amounts of rainfall are exemplified by Wayne & Genevie Riner who had measured 9.58″ through the morning of June 20 (34.10 in 2019), on Long Ridge of Sandy Ridge in southern Dickenson County, Va.

Development of an air mass with extreme instability is the big concern, with simply sick or outrageous convective energy being predicted by multiple forecast models along and just behind a surface warm frontal boundary in developing W-NW flow aloft. Past climatology of similar settings dictates that this is an ominous signal. Storms will fire within and along the gradient of extremely unstable air.

A very dry, cool air mass over the Upper Great Lakes and across the northeastern USA will be in dramatic contrast to a very humid, moisture laden air mass overspreading the Ohio-Tennessee valleys and southern Appalachians.

Current 500 MB (18,000 Feet) Flow Field

A strong (for June) upper air trough digging into the Pacific Northwest will help develop upper ridging downstream, with the Mountain Empire becoming located on the eastern side of a developing ridge axis in W-NW flow aloft into this weekend. Very moist and extremely unstable air will be developing in low-levels of the atmosphere with off-the-charts values of lifted indices, CAPE, supercell potential, etc being forecast (some of the highest values I have seen over this part of the world on forecast models).

Interactive Full-Screen Doppler Radar

Ideally, the worst storm clusters will fire southwest and northeast of the Mountain Empire (bad for those locations), but that can simply not yet be known and it will be surprising if the mountains are not impacted given the gradient of unstable air predicted by models.

Stay tuned to NOAA Weather Radio and your favorite media sources for updates on this potentially dangerous weather setting expected to develop this weekend.