Partly-mostly cloudy. Chance of a hit-miss shower or storm. Winds SSE-SSW 5-10 mph, with higher gusts, on mountain ridges-plateaus below 2700 feet. Winds S-SW at 10-20 mph, with higher gusts, on mountain ridges above 2700 feet. Temperatures varying from upper 50s to lower 60s in cooler valleys, with areas of fog, to mid-upper 60s.
Saturday Afternoon
Partly to mostly cloudy. Chance of scattered showers & thunderstorms. Winds SSW-SW 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges-plateaus. Temperatures varying from lower 70s in upper elevations to the upper 70s to lower 80s ( hotter south into the Great Valley of eastern Tennessee and southwest Virginia ).
Saturday Night Into Sunday Morning
Mostly cloudy. Chance of a shower or thunderstorm. Winds SSW-WSW 5-15 mph mid-upper elevation mountain ridges. Temperatures widespread in the 60s.
Sunday Afternoon
Showers & downpours in thunderstorms likely. Locally heavy rainfall amounts. Winds becoming W-NW at 5-10 mph, with higher gusts. Temperatures varying from the lower 60s in upper elevations to upper 60s to lower 70s. Low clouds and fog along higher mountain ridges. Patchy fog possible in other locations.
Sunday Night Into Monday
Showers & thunderstorms giving way to showers. Locally heavy rain possible into the overnight. Areas of fog ( dense along higher mountain ridges ). Winds becoming WNW-N at 5-10 mph, with higher gusts, along mid to upper elevation mountain ridges. Temperatures varying from mid-upper 50s to the low-mid 60s ( coolest in upper elevations ).
Following a dry first-half to September it appears that a cold frontal boundary will finally bring some significant rainfall to the mountain area this weekend.
Doppler Rainfall Estimate For Friday – September 16
Local hit-miss downpours developed Friday ( above ), with more of the same possible Saturday before activity increases Sunday.
NAM 12 KM Model Total Rainfall Forecast To 2:00 PM Sunday – September 18
The main focus of heavier rains will be on Sunday for locales along and west of the Cumberland Mountains ( shifting east toward the Great Valley by late in the day ). Exact timing, of course, subject to change as activity actually develops.
NAM 12 KM Model Total Rainfall Forecast To 8:00 PM Sunday – September 18
If activity develops early along the Cumberland range the day will feature much lower temperatures and low clouds, with some orographic lifting across the high terrain.
European 51-Member Ensemble MEAN 500 MB Height Anomalies – DAYS 4 to 8
While much lower dewpoint air will again create some nice, cool nights during early-middle portions of next week, the current trend is for a rebuilding of 500 MB heights across the southeastern USA during September 20-24.
European 51-Member Ensemble MEAN 850 MB Temp Anomalies – DAYS 4 to 8
Daytime temperatures will again surge above average, with at least the potential for some more 90 degree days in the Great Valley ( especially if total rainfall is not heavy ).
Track Forecast For Typhoon Malakas
However, current extended trends suggest that heat next week will give way to MUCH cooler air and the first true shot of Canadian Chill during the final days of this month as a recurving typhoon in the western Pacific links up with the Polar Jetstream to force downstream changes in the flow pattern across North America. Stay tuned!
Partly-mostly clear. Areas of fog. Light winds. Temps varying from 50s in cooler mountain valleys to the mid-upper 60s on exposed middle elevation ridges-plateaus.
Wednesday Afternoon
Partly cloudy & warm. Chance of hit or miss showers and thunderstorms. NW-NNE winds 5-10 mph. Temperatures varying from 70s in upper elevations to the low-middle 80s ( hotter south into the Great Valley ).
Wednesday Night Into Thursday Morning
Becoming mostly clear following any early evening activity. Light NE-ENE winds generally less than 10 mph along mid-upper elevation mountain ridges. Areas of valley fog. Temps varying from upper 40s to lower 50s in cooler mountain valleys to the upper 50s-lower 60s.
Thursday Afternoon
Partly cloudy. Small chance of a hit-miss shower or storm. Light NNE to ENE winds. Temperatures varying from 70s in upper elevations to the lower-mid 80s ( hotter south into the Great Valley ).
Thursday Night Into Friday Morning
Partly-mostly clear. Winds ESE-SSE 5-15 mph along mid to upper elevation mountain ridges. Temperatures varying from 50s in cooler mountain valley to the mid-upper 60s.
Friday Afternoon
Partly-mostly cloudy. Chance of hit-miss showers-storms. SSE-SSW winds 5-10 mph, with some higher gusts. Temps varying from 70s in the upper elevations to lower-middle 80s ( hotter south into the Great Valley ).
Weather Discussion ( Weak Front )
An increase in the chance of showers & thunderstorms is expected into this weekend, following a drier than average first half of September 2016.
Above Ground Roots – Northern Woods Swamp Forest of High Knob Massif
The northern woods of the High Knob Massif remain damp, and if one did not know this area they would never know that September had been drier than average.
*The lower than normal lake level at Big Cherry Lake, due largely to much release during Summer 2016 to augment the Powell River, reveals that the regional pattern has been drier than average.
*Conditions In Upper Valley of Big Cherry Lake Basin on Sept 14
A simply HUGE contrast in conditions were observed during September 14 as afternoon temps in the valley dropped into the 60s, with clouds and local downpours, versus lower 90s at the same time in the Tri-Cities of the Great Valley.
*Conditions In Upper Valley of Big Cherry Lake Basin on Sept 15
Another large spread in conditions were observed during the afternoon hours of September 15, despite partly cloudy skies above the High Knob Massif.
*Data courtesy of Field Studies In Microclimatology at the University Of Virginia’s College At Wise using highly accurate, National Weather Service calibrated temperature sensors.
NAM 12 KM Model Total Rainfall Forecast Next 84-Hours
The NAM Model is showing the potential for some heavy rainfall by Sunday into Monday of September 18-19. Stay tuned for updates on this possibility.
Previous Discussion
The breaking news at the time of this update was the upgrade of Invest 93L to Tropical Storm Julia by the National Hurricane Center.
Infrared Satellite Image At 11:45 PM on September 13, 2016
The forecast going into Wednesday is for a weak front to move into the mountains and trigger hit-miss showers and thunderstorms into the afternoon. A wind shift then allows lower dewpoint air, at mid-upper elevations especially, to invade the Cumberland Mountains into Thursday morning.
National Hurricane Center Track For Julia
Although Julia is not expected to directly impact the local area, it could slow the weak boundary and/or aid sinking aloft and development of drier air depending upon its strength and movement. This is the uncertainty in the current forecast period that may need to be updated*.
*Temperatures into Thursday morning may not be as cool as I am currently forecasting in mountain valleys if the boundary is not able to push south-southwest of the High Knob Massif-Tennessee Valley Divide. On the other hand, if deep convection continues around Julia and it moves more east than north then sinking air aloft could reinforce the development of drier air over the area into Thursday-Friday ( dissipating the boundary and enhancing easterly to northeasterly flow into the area ).
European 51-Member Ensemble MEAN 500 MB Height Anomalies Forecast
In the big picture, on the synoptic-scale, nothing has really changed from my previous outlooks with an above average temperature pattern ( especially by day ) continuing. If the Tri-Cities do not reach 60 days of 90+ degree heat it will not be because this pattern is not favorable, especially given an increasing precipitation deficit across the Great Valley.
500 MB heights remain well above average during the next week to ten days, decreasing only slightly toward 588 dkm on the VA-TN border during the 6-10 day period ( September 19-23 ).
European 51-Member Ensemble MEAN 500 MB Height Anomalies Forecast
Although sun angles are decreasing and nights growing longer, the persistence of these anomalous heights over dry ground ( especially in the Tennessee Valley ) will continue to keep temperatures above model guidance.
Exceptions being on days that feature more cloudiness and/or showers-thunderstorms. Rainfall, for the most part, remaining limited into at least the beginning of this weekend as it looks now.
European 51-Member Ensemble MEAN 850 MB Temp Anomalies Forecast
The MEAN of the 51-Member European Model Ensembles is for temperatures to decrease a little, with emphasis being on little, amid the 6-10 day forecast period of September 19-23 ( below ). Looking at individual days; however, it would be no surprise for another day, or two, to hit 90 degrees in the TRI next week! If their ground can moisten then this threat may finally end.
European 51-Member Ensemble MEAN 850 MB Temp Anomalies Forecast
As I noted previously, it will likely be late September-early October before the southern Appalachians have a chance to actually feel a true push of autumn air.
As noted by the rapid spin-up of Julia, things can change quickly so stay tuned for updates. In this case, the synoptic-scale pattern has been rather stable to increase confidence in the persistence of this big picture setting for a while longer.
Cloudy with showers and possible thunder into early overnight, then a chance for rain showers into morning. Winds becoming NW-N at 5-10 mph, with higher gusts. Temperatures dropping into the mid 50s to middle 60s, coolest at highest elevations.
Sunday Afternoon
Becoming partly-mostly sunny. Cooler and less humid with refreshing air. Winds N-NE at generally less than 10 mph. Temperatures varying from 60s in upper elevations to the mid-upper 70s.
Sunday Night Into Monday Morning
Partly to mostly clear. SE-SSE winds mostly less than 10 mph along mid-upper elevation mountain ridges. Temps varying from mid-upper 40s in cooler mountain valleys to the mid-upper 50s. Areas of fog, especially along lakes and in main river valleys.
Monday Afternoon
Partly to mostly cloudy. Slight chance of a shower or sprinkle. Light SSE-SSW winds. Temperatures varying from low 70s in upper elevations to the lower 80s ( warmer south into the Great Valley ).
Monday Night Into Tuesday
Partly to mostly clear. S-SW winds 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges. Temps varying from 50 to 55 degrees in cooler mountain valleys to the lower 60s. Areas of fog around lakes and rivers.
Weather Discussion ( Warm Trend )
A cold front featuring scattered showers and local downpours will continue passing across the mountains Saturday night into Sunday morning.
Doppler Radar At 9:29 PM Saturday – September 10, 2016
A cooler, refreshing air mass follows during Sunday into Sunday night-Monday morning with another taste of early autumn in the mountains.
European 51-Member Ensemble MEAN 500 MB Height Anomalies – DAYS 3 to 7
Nothing has changed in the big picture from my previous outlook, with MEAN 500 MB Heights continuing to run above average with ridging over the southeastern USA ( above ) during the bulk of this coming week.
European 51-Member MEAN 850 MB Temp Anomalies – DAYS 3 to 7
Following cooling felt in the short-term this will return and continue the above to much above average temperature trend observed so far in September ( especially by day ).
Although the mountains will not reach 90 degrees, the Great Valley will have a chance to pad the all-time record number of 90 degree days now observed in the Tri-Cities.
Mostly clear. Areas of valley fog. WNW-NW winds mostly less than 10 mph on mid-upper elevation mountain ridges. Temperatures varying from 50s in cooler mountain valleys to the mid-upper 60s.
Thursday Afternoon
Partly cloudy. Unseasonably warm for the season. Light SW-W winds. Temperatures varying from 70s in upper elevations to the mid-upper 80s ( hotter south into the Great Valley of eastern Tennessee ).
Thursday Night Into Friday Morning
Partly-mostly cloudy. Areas of valley fog. Winds SW-WNW 5-10 mph along middle-upper elevation ridges & plateaus. Temperatures varying from upper 50s-lower 60s in cooler valleys to the upper 60s to around 70 degrees.
Friday Afternoon
Partly cloudy. More humid. Small chance of a hit-miss shower or thunderstorm. Light & variable winds. Temps varying from 70s in upper elevations to the middle-upper 80s ( hotter south into the Great Appalachian Valley ).
Friday Night Into Saturday Morning
Partly to mostly cloudy. Winds SSW-WSW at 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges and plateaus. Temperatures widespread in the 60s.
Saturday Afternoon
Partly cloudy. Continued unseasonably hot for the season. Small chance of a hit-miss shower or storm. Winds SW-W at 5-10 mph, with higher gusts. Temps varying from 70s in upper elevations to the mid-upper 80s ( hotter south into the Great Valley ).
Saturday Night Into Sunday Morning
Partly-mostly cloudy. Small chance of showers. Winds becoming NW-NNE at 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges-plateaus. Temps dropping into the mid 50s to mid 60s ( coolest at highest elevations ).
Low temperatures in the 40s and 50s will be likely by Sunday Night into Monday, with coolest conditions expected amid mountain valleys at middle-upper elevations.
Weather Discussion ( Dry & Warm )
The early Meteorological Autumn season of 2016 finds the Mountain Empire caught amid a dry weather pattern that is being dominated by a sinking air regime.
Wide Floor of High Elevation Wetland Valley In High Knob Massif – September 6
The sinking air has allowed for large day-to-night temperature spreads, especially amid higher mountain valleys, with 40s and 50s felt during this first week of September 2016.
Unseasonable warmth ( heat ) by day will continue through the first half of this weekend until a cold front passes by Saturday Night into Sunday. While a chance for showers, or a thunderstorm, in hit-miss fashion can not be ruled out most of the time ( and many places ) will remain dry.
European 51-Member Ensemble MEAN 500 MB Height Anomaly Forecast
While drier, lower dewpoint air, will again surge across the mountains Sunday into Monday, to generate more cool nights, unseasonable warmth returns by day as 500 MB heights remain well above average for this time during much of next week.
European 51-Member Ensemble MEAN 500 MB Height Anomaly Forecast
This could add on yet more 90s for the Great Valley to pad what by then will be an all-time record number of days with 90 degree or higher temperatures during a year.
European 51-Member Ensemble MEAN 850 MB Temp Anomaly Forecast
Cooler nights from Sunday into early next week are not really reflected on these graphics, since days trend back above to much above average, amid sinking air, to keep MEAN temperatures above average through much of next week.
European 51-Member Ensemble MEAN 850 MB Temp Anomaly Forecast
Although the change of seasons is really showing up at high latitudes, and high elevations in the Rockies, it appears that the Mountain Empire will have to wait until some point in the second half of September-early October before feeling more than just lower dewpoint ( dry air ) induced cooling at night ( i.e., a strong surge of true Canadian air ).
*Up to 10″ of snow was reported during this first week of September in Showdown, Montana, within the Little Belt Mountains well to the north-northeast of Bozeman.
The second half of September is getting close, so stay tuned as we watch autumn changes increase across the Northern Hemisphere during coming weeks.
Mostly clear. Cool. Areas of valley fog. Light winds. Temperatures varying from 40s in cooler mountain valleys of mid-upper elevations to the lower-middle 50s.
Sunday Afternoon
Partly-mostly sunny. Light N-NE winds mostly less than 10 mph. Temperatures varying from 60s at highest elevations to the upper 70s to lower 80s ( warmer in the Great Valley toward the Tri-Cities ).
Sunday Night Into Monday Morning
Mostly clear. Areas of valley fog. Light winds. Temperatures varying from upper 40s to lower 50s in cooler mountain valleys to the upper 50s to lower 60s.
Monday Afternoon
Partly-mostly sunny. Warmer. Winds NW-N generally less than 10 mph. Temperatures varying from low-mid 70s in upper elevations to the lower-middle 80s ( hotter south into the Great Valley of eastern Tennessee ).
Monday Night Into Tuesday Morning
Partly cloudy. Areas of valley fog. Winds WNW-NW at 5-10 mph along mid-upper elevation mountain ridges. Temps varying from 50s in cooler valleys to the mid-upper 60s.
Tuesday Afternoon
Partly cloudy. Winds WNW-NW 5-10 mph. Temps varying from 70s in upper elevations to the mid-upper 80s ( hotter south into the Great Valley toward the Tri-Cities ).
Late Summer-early Meteorological Autumn heat wave conditions are expected through mid-late week amid a subsidence regime of sinking air in the wake of western Atlantic tropical activity. Due to sinking air I have updated the forecast to reduce humidity, this will allow for significant day-to-night temperature spreads ( most pronounced amid mountain valleys ) and make heat tolerable until humidity increases along an initial front by next weekend into the middle of September ( current trend ).
Weather Discussion ( Summer Returns )
A welcomed and refreshing break from the muggy days of August is being enjoyed during this Labor Day Holiday.
Late Summer In High Wetland Valley of High Knob Massif
Temperatures have been in the 40s amid higher mountain valleys with 50s widespread across lower-middle elevations. Very nice!
Temperatures and Relative Humidity In Clintwood – September 4, 2016
A heavy dew has occurred in valleys as the air is approaching saturation in lower elevation mountain valleys at 3:30 AM.
European 51-Member Ensemble MEAN 500 MB Height Anomlies – DAYS 3-7
However, as I advertised last week, sinking air in the wake of Hermine will help rebuild a large upper ridge over the region with rising temperatures and late summer-early Meteorological Autumn heat wave conditions expected to redevelop during this week.
European 51-Member Ensemble MEAN 850 MB TEMP Anomaly Forecast
The 51-Member European Ensemble MEAN shows this well with above to much above average temperatures expected during the Tuesday-Saturday period ( September 6-10 ).
There is little doubt that this will be sufficient to allow the Tri-Cities to break the all-time record for the most 90s in a year ( or summer season ), especially given the continuation of dry ground versus average over the Great Valley.
Meteorological Summer Recap For The Great Valley Of Eastern Tennessee
Summer 2016 was a blaze amid the Great Valley, with 77 days at or above 90 degrees during June-August in Chattanooga, 57 days in Knoxville and 52 days in the Tri-Cities.
Meteorological Summer consists of June-August and ended up being the second warmest on record through the Great Valley.
The Summer 2016 average varied from 77.1 degrees in the Tri-Cities to 82.5 degrees in Chattanooga. This compares with observed averages in the 60s for upper elevations in the High Knob Massif to Black Mountain corridor of the Cumberland Mountains.
The June-August average temperature for Clintwood ended up at exactly 72.0 degrees.
Partly cloudy & hazy. Humid. Areas of dense valley fog. Light southerly winds along mid-upper elevation ridges. Temps in the 60s to around 70 degrees.
Sunday Afternoon
Partly sunny. Hazy & humid. Chance of hit-miss showers and downpours in thunderstorms. Winds becoming E-NE at 5-10 mph. Temperatures varying from middle to upper 70s in highest elevations to mid-upper 80s ( hotter southward into the Great Valley ).
Sunday Night Into Monday Morning
Chance of hit-miss evening showers-storms; otherwise, partly cloudy. Areas of dense fog. E-SE winds 5-10 mph along mid to upper elevation mountain ridges. Temps varying from upper 50s to the upper 60s.
Monday Afternoon
Partly cloudy. Chance of hit-miss showers-thunderstorms. Winds ENE to NE 5-10 mph, with some higher gusts. Temps varying from low-mid 70s in upper elevations to the lower-middle 80s ( hotter south into the Great Valley ).
Monday Night Into Tuesday
Evening thunderstorms diminishing. Partly cloudy & humid. Areas of dense fog. Light E-NE winds along mid-upper elevation ridges. Temperatures in the 60s to around 70 degrees.
Tuesday Afternoon
Partly cloudy. Chance of hit-miss showers-thunderstorms. Winds E to NE 3-10 mph. Temperatures varying from mid-upper 70s in upper elevations to mid-upper 80s ( hotter south into the Great Valley ).
Tuesday Night Into Wednesday Morning
Chance of hit-miss showers & downpours in thunderstorms. Humid. Areas of fog. Light & variable winds. Temps in the 60s to around 70 degrees.
Weather Discussion ( Final Days )
Late summer heat and humidity helped trigger some booming storms across the mountain area Monday, in hit or miss manner as forecast, with downpours and gusty winds.
Clouds Tower Above Cumberland In Late Summer Heat
Rainfall totals locally topped 0.50″ in just 15-20 minutes in places that got hit hardest with downpours ( e.g., Big Cherry Lake Basin and along Pine Mountain from Breaks Interstate Park southwest toward Pound Gap to note a couple areas ).
The same pattern holds during Tuesday-Wednesday before a cold front arrives Thursday, with cooler and much less humid air again taking control Friday into the Labor Day Holiday Weekend ( beyond that sinking air in wake of passing tropical systems may rebuild the heat ridge ).
Model Spaghetti Tracks On Pre-Hermine Development
Models have finally come into general agreement on the likely formation of former Invest 99L, now Tropical Depression 9, with a movement across northern Florida and back into the Atlantic being the one currently favored.
National Hurricane Center 5-Day Track Forecast For TD9
It is not impossible, of course, that TD8 could beat TD9 to the Hermine name as it briefly intensifies over the Gulf Stream approaching the North Carolina Outer Banks.
National Hurricane Center 5-Day Forecast Track For TD8
Sinking air in the wake of these, by late in the weekend-early next week, will help rebuild heights to the west and likely allow the TRI to add a few more 90s that could help them reach the record for the most 90-degree days ever officially observed in the Tri-Cities.
Shorter days and longer nights will eventually take its toll on summer heat, especially into mid-late September when most years feature significant autumn color changes amid upper elevations of the High Knob Massif ( above 2700-3000 feet ). I, for one, greatly look forward to this color season!
Previous Discussion
The final days of August means it is also the final days for Meteorological Summer 2016. Many will say good riddance given the nearly relentless humidity in the mountains and heat+humidity in the Great Appalachian Valley.
August 27 Temperature-RH at NWS Station In Clintwood
August 27 ( Saturday ) was one of the hottest days of the entire summer ( and the hottest day in August ) within the Cumberland Mountains, with the above temps being recorded in Clintwood between 6:40 AM and 6:40 PM.
The 89.4 degrees PM MAX combined with a muggy 66 degree dewpoint reading ( 48% relative humidity ) to generate a 93 degree Heat Index.
Doppler Radar Rainfall Estimate For August 27, 2016
A few showers and downpours in thunderstorms managed to develop, with some of the heaviest action just southwest of Cumberland Gap. More downpours fell along Guest River Gorge, close to ( if not over ) the rain gauge of Jerry Rose where he’d already measured more than 7.00″ in August.
Most places remained dry.
NAM 12 KM Model Total Rainfall Forecast Next 3-Days
The same pattern holds through the next several days, with a little more cloud coverage over the mountains and a little better coverage of hit or miss showers-storms. Note that emphasis continues to be on hit-miss activity that fights against sinking air aloft to develop amid heat-instability.
Meanwhile, the saga of Invest 99L continues!
Model Spaghetti Tracks For Invest 99L
While possible tracks ( above ) are spread about as wide as they can get, the spread in intensity forecasts ( below ) are perhaps even more impressive with variations from a CAT 4 to not being more than a depression ( at best ).
Model Spaghetti Intensity Forecast For Invest 99L
Even the typically dependable European Model has had large run-to-run variations, and large differences among it’s ensembles. Stay tuned!
Partly cloudy. Areas of dense valley fog. Winds S to SW at 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges. Temperatures in the upper 50s to mid-upper 60s.
Thursday Afternoon
A chance of hit-miss showers & thunderstorms. Partly cloudy. Hazy. Winds S-SW at 5-10 mph, with some higher gusts along highest ridges. Temperatures varying from the low-mid 70s in upper elevations to the lower-middle 80s.
Thursday Night Into Friday Morning
Partly to mostly clear. Areas of dense valley fog. SW winds becoming northerly into morning at 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges. Temps varying from lower 60s to around 70 degrees.
Friday Afternoon
Partly to mostly sunny. Hot. Light N to NE winds. Temps varying from middle-upper 70s in upper elevations to the middle to upper 80s ( hotter south into the Great Valley ).
Friday Night Into Saturday Morning
Mostly clear. Areas of dense valley fog. Light E-SE winds. Temperatures varying from 50s in the coolest mountain valleys ( mid-upper elevations ) to the mid-upper 60s.
Saturday Afternoon
Partly sunny. Hot & humid. Chance of a hit-miss shower or thunderstorm. Light SSE-SSW winds. Temps varying from mid 70s to around 80 degrees at highest elevations to upper 80s to around 90 degrees ( hotter into the Great Valley ).
Saturday Night Into Sunday Morning
Partly cloudy. Humid. Areas of dense valley fog. Light southerly winds along mid-upper elevation ridges. Temps in the 60s to around 70 degrees.
Weather Discussion ( More Summer )
A heat ridge centered near the Great Smokies is well known climatologically as a heat maker for the Mountain Empire, even in the final days of the Meteorological Season.
Sinking Air Beneath Late Summer Heat Ridge – Northern Dickenson County
Although some afternoon cumulus formed Thursday and Friday, especially along major lifting zones like the High Knob Massif, the atmosphere was clearly being dominated by subsidence aloft.
Mathematically deriving the Law Of Conservation Of Mass, from which various forms of the Continuity Equation is obtained, it is easy to develop a basic Subsidence Model for the atmosphere that clearly illustrates the relationship between rising & sinking air.
Essentially, low-level rising in one region of the atmosphere must be compensated for by large-scale sinking within another region. While we often focus on convection that forms in a ring around high pressure centers it is seldom noted how air spreading out aloft above the convection acts to support and reinforce, via compensative subsidence, the adjacent high pressure.
Model Spaghetti Forecast Track For Invest 99L
So even as Invest 99L struggles, and models struggle with what it will eventually do, there will be significant low-level convergence across the Gulf of Mexico into the Upper Midwest through coming days that will continue to support the large-scale subsidence of air that is dominating the Mountain Empire. The result being heat, humidity and little rain ( only localized storms in places where orographics and/or instability may briefly overcome sinking ).
Eventually, as is true of all things, this will change but for now this is the Bottom Line of the Big Picture.
Model Spaghetti Intensity Forecast For Invest 99L
*While rising-sinking ( outside of that orographically forced ) is not as coupled in mid-latitudes on the synoptic-scale as it is amid the tropics, the principle still applies and regions where synoptic high pressure is favored can be ( and often are ) aided by these processes ( since mass can be neither created nor destroyed, only rearranged in space & time and/or transformed in ways that still result in the total mass remaining unchanged ).
Previous Discussion
Following a short-stretch of simply gorgeous conditions that featured a few 40s in high mountain valleys, the heat of Summer 2016 is returning.
Pristine Water In Big Cherry Lake Basin – August 22, 2016
The lazy, hazy, crazy days of August also feature plenty of noise courtesy of Annual Cicadas ( below ) that tend to be plentiful at this time of year.
These are in a different genus from Periodical Cicadas that erupt in cycles of 13-17 years, forming one of the greatest natural events on planet Earth which is endemic to eastern North America.
National Weather Service stations in Wise and Clintwood have not recorded a day above the low 80s during the past seven days, since August 17 ( the MAX being recorded for the 24-hours ending during the AM of August 18 ).
NWS Station – UVA Wise – Observers Bob Vangundy & Layton Gardner
The morning of August 23 has been the coolest, with 52 degrees on the plateau at the University Of Virginia’s College At Wise and 40s in adjacent valleys from the City of Norton upward into the high country of the High Knob Massif. A brief preview of Autumn!
Dense fog prevented the MIN from dropping below 54 degrees in Clintwood and most valleys across the lower elevations ( below 2000 feet elevation ).
NWS Station In Clintwood – Observer Wayne Browning
August rainfall of exactly 3.56″ in both Wise and Clintwood might suggest that rains had fallen evenly during the past 3 weeks; however, that is not the case as exemplified by 5.59″ measured in the official rain gauge at the City of Norton Water Plant by Andrew Greear & Staff, and more than 7.00″ measured by Jerry Rose in the Crab Orchard community near Guest River Gorge of the High Knob Massif.
August rains have also varied significantly across the Big Cherry Lake Basin, with 4.38″ at Big Cherry Dam being in contrast to more than 6.00″ across the basin head near the High Knob peak.
NAM 12 KM Model Precipitable Water Forecast At 8 AM Saturday – August 27
Following a chance for hit-miss showers & thunderstorms on Thursday, drier air aloft with subsidence will lower the total precipitable water values in the atmosphere Friday into Saturday to aid late season summer heating.
From August 25 onward through the remainder of the year only 4 days have ever been able to break 90 degrees in Wise, such that the window for this type of heat is closing with shorter days, longer nights and lowering sun angles.
In order to break 90 degrees from this point forward, in the middle elevations of the Cumberland Mountains ( between 2000-3000 ft ), everything must fall into perfect alignment ( mainly…either dry ground + few to no clouds + sinking air and/or normal wetness + few to no clouds with strongly sinking air ).
So the key to perhaps hitting 90 again ( for the 2nd time ) in either Wise or Clintwood will be for the air to dry out aloft with subsidence to prevent cloud formation. It is difficult to do on the heels of an average to above average rainfall summer, but Friday-Saturday will attempt this feat.
Meanwhile, temperatures in the Great Valley of eastern Tennessee will blaze under conditions like this with downslope flow in lower levels combined with subsidence aloft over ground that remains drier than average in wake of a very dry June 1-August 15 period.
Spaghetti Model Tracks For Invest 99L
The main focus from this weekend into next week will be on Invest 99L and its potential for development into a tropical storm and hurricane. Will it impact the Appalachians in a direct manner, with heavy rainfall? That is impossible to tell at this point in time. Stay tuned for updates.
However, some impact is almost certain as even if the storm’s rain shield passes well to the east, a zone of strong subsidence will be to its west and help prolong the heat of Summer 2016 for places that get under its ring of sinking air ( via the Law of Conservation of Mass ).
Caution For Swift Water On Steep Creeks Draining The High Knob Massif Into Monday
Sunday Night Into Monday
Mostly clear. Cooler & refreshing. Areas of dense valley fog. Winds WNW-NNW 5-15 mph, with higher gusts, along mid-upper elevation mountain ridges. Temperatures in the 50s to near 60 degrees ( 50-55 degrees in cooler locations ).
Monday Afternoon
Partly sunny. Beautiful skies & pleasant. Winds NW-N at generally less than 10 mph. Temperatures varying from 60s in upper elevations to the mid-upper 70s.
Monday Night Into Tuesday Morning
Clear & cool. Areas of dense valley fog. Light winds, except winds becoming E-SSE at 5-10 mph along the highest ridges. Temperatures varying from 40s in cooler mountain valleys of mid-upper elevations with limited fog to the mid-upper 50s on exposed middle-upper elevation ridges.
Tuesday Afternoon
Partly-mostly sunny. Warmer. Light SE-S winds. Temperatures varying from upper 60s to lower 70s at highest elevations to the upper 70s to lower 80s.
Tuesday Night Into Wednesday Morning
Partly cloudy. Areas of dense valley fog. Winds S to SSW at 5-10 mph, with some higher gusts, on mid-upper elevation mountain ridges. Temperatures varying from the 50s to low-mid 60s ( coolest in mountain valleys ).
Wednesday Afternoon
Partly cloudy. Hazier. A chance of hit-miss showers & thunderstorms. Winds SSW-SW 5-10 mph, with higher gusts. Temperatures varying from lower 70s at highest elevations to the upper 70s to low-mid 80s.
Wednesday Night Into Thursday Morning
Partly cloudy. Chance of an evening shower or storm. Areas of dense valley fog. Winds SSW-W at 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges. Temperatures in the upper 50s to mid-upper 60s.
Weather Discussion ( Brief Break )
( Cumulus congestus ) and other forms along an orographic wave line
High Knob Massif Webcam – University Of Virginia’s College At Wise
Except for lingering orographic clouds, a push of much drier air finally made it into the Cumberland Mountains during mid-late afternoon hours of Sunday ( Aug 21 ).
Day-time MAXS varied in the 60s to lower 70s ( 72.8 degrees officially in Clintwood ).
High Knob Massif Webcam – University Of Virginia’s College At Wise
Rainfall was enough to force strong rises on steep creeks draining the High Knob Massif, which will remain swift into Monday before diminishing.
Big Stony Creek of High Knob Massif – Stream Level August 15-21, 2016
A water level rise to near the Red Alert Stage on Big Stony Creek is a good indicator for other steep creeks draining the high country, where this event has pushed 2016 precipitation totals into the 45.00″ to 50.00″ range ( 18.00-20.00″+ during Summer 2016 ).
Refreshing Air Begins To Arrive – Late Afternoon on August 21, 2016
The main focus now is on a brief preview of Autumn 2016 with refreshing, cooler air for a couple days before muggy air returns later Wednesday into Thursday. A brief break!
Monday AM ( August 22 ) will feature the coolest conditions at highest elevations, while Tuesday AM ( August 23 ) will be the coolest in mountain valleys.
MIN temperatures will drop into the 50-55 degree range in cooler places into Monday AM ( especially at highest elevations ) as fog develops and becomes dense in many valleys ( especially at lower to middle elevations ).
MIN temperatures will drop well into the 40s within higher valleys by Tuesday AM, with valleys having little to no fog being coolest versus low-mid 50s in valleys that develop fog ( again, fog will become most widespread at the lower elevations ).
Showers & Tropical Downpours In Thunderstorms Will Remain Possible Into Sunday. Much Drier Air & Cooler Temperatures Are Expected Late Sunday Into Monday.
Remain Alert For The Potential Of Strong Rises On Creeks and Ponding Of Water Along Roads And In Typical Low-lying Flood Prone Locations
A significant cold front will be crossing the mountains by late Sunday with showers & downpours in storms possible along and ahead of the front. Much drier, cooler and refreshing air will be transported into the area Sunday Night into Monday.
Overnight Into Saturday Morning
Chance of a local shower; otherwise, partly to mostly cloudy with areas of fog. Humid. Light winds. Temps in the 60s.
Saturday Afternoon
A chance for showers & thunderstorms. Winds SSW-SW 5-15 mph, with higher gusts. Temperatures varying from 60s at highest elevations to the middle 70s to lower 80s.
Saturday Night Into Mid-Morning Sunday
Showers & thunderstorms developing. Locally heavy rain. SW winds 5-15 mph, with higher gusts, on mountain ridges and plateaus below 2700 feet. Winds SW-W at 10-20 mph, with higher gusts, along upper elevation mountain ridges. Temperatures in the 60s.
Sunday Afternoon
Showers & thunderstorms into mid-late PM ( especially along and south of the High Knob Massif ). Locally heavy rainfall. Refreshing air arriving late. Winds becoming WNW to NW 5-15 mph, with higher gusts. Temps varying from 60s in upper elevations to the mid-upper 70s.
Sunday Night Into Monday
Mostly clear. Cooler & refreshing. Areas of dense valley fog. Winds WNW-NNW 5-15 mph, with higher gusts, along mid-upper elevation mountain ridges. Temperatures in the 50s to near 60 degrees ( 50-55 degrees in cooler locations ).
Monday Afternoon
Partly sunny. Beautiful skies & pleasant. Winds NW-N at generally less than 10 mph. Temperatures varying from 60s in upper elevations to the mid-upper 70s.
Cooler mountain valleys, mainly at mid-upper elevations, will drop into the 40s during Monday Night into Tuesday AM ( with somewhat milder low-mid 50s in foggy valleys ).
Weather Discussion ( Refreshing Air )
An update near Midnight on Saturday is for a slowing of the cold frontal passage Sunday, with new model runs being a few hours slower to clear the area than yesterday.
Models have also increased rainfall amounts, such that at least localized high water problems could arise.
NAM 12 KM Model Precipitable Water Forecast At 5 PM Sunday – August 21
The NAM 12 KM Model has the drier air still just northwest of the Virginia-Kentucky border at 5:00 PM Sunday ( above in brown-blue colors ), with timing being near sunset before it really enters the Cumberland Mountains ( below ).
While this could again made it rough on NASCAR fans, it also means that downpours with a heavy rain potential will linger until deep moisture moves southeast.
NAM 12 KM Model Precipitable Water Forecast At 8 PM Sunday – August 21
Given downpours of rain Saturday the potential for strong rises on creeks will need to be monitored, especially if rain becomes heavy and/or prolonged in nature Sunday. Remain alert for ponding of water along roadways and in typical low-lying, flood prone locations.
The European Model, which did very well with placement of heavier rainfall Saturday, is forecasting the heaviest rains to develop Sunday along the front. The latest NAM group have trended that way, so please remain alert as at least local high water problems could arise.
Previous Discussion
Although humidity, showers & downpours in storms will remain possible ( become likely ) into early Sunday AM, the headline making news is a welcomed push of refreshing air poised to engulf this great mountain landscape from Sunday afternoon into Monday. It will feel awesome!
High Knob Massif Webcam – University Of Virginia’s College At Wise
A general 1.00″ to 3.00″+ of rain has fallen across the mountain area this week, with frequent hit-miss showers & downpours in thunderstorms and often spectacular tropical skies.
High Knob Massif Webcam – University Of Virginia’s College At Wise
August 18-19 featured MAX temperatures in the 70s in Norton-Wise, Sandy Ridge, and Clintwood, with 60s at highest elevations in the High Knob Massif.
*A 78 degree MAX in Clintwood on August 19 will be recorded for the 24-hour period ending at 7:00 AM on August 20 ( below ).
National Weather Service Daily Stats For Clintwood
Short-range models continue to show the chance for downpours in showers & thunderstorms Saturday into Sunday Morning, especially along-ahead of a cold front that will finally push away the tropical air and bring simply spectacular conditions to the area for a while.
NAM 4 KM Model Total Rainfall Forecast Into Sunday
The high resolution NAM 4 KM shows hit-miss downpours, with the NAM 12 KM suggesting best coverage toward the south across the Tennessee Valley & Cumberland Plateau into the TN-NC border area.
NAM 12 KM Model Rainfall Forecast Next 48-Hours
Regardless of the eventual coverage, cooler and much drier air will sweep across the Mountain Empire from northwest to southeast beginning about mid-morning to mid-day on Sunday. A most welcomed and long-awaited change.
Showers & Tropical Downpours In Thunderstorms Will Occur At Times Into This Weekend-Early Next Week, With Heavy To Locally Excessive Rainfall Possible
Any thunderstorm at this time of year can turn locally strong to severe through coming days along and in advance of cold fronts. Heavy to locally excessive rainfall will be possible with a nearly stationary boundary across the mountain area Thursday-Friday, and again late in this weekend along a stronger cold front.
Much less humid air is expected to arrive behind the second cold front by August 22-25 ( with much cooler nights ).
Tuesday Night Into Wednesday Morning
A chance of hit-miss showers & thunderstorms; otherwise, partly cloudy. Areas of fog. Winds SW-W 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges. Temperatures in the 60s to lower 70s.
Wednesday Afternoon
Partly-mostly cloudy. A good chance for showers & tropical downpours in thunderstorms. Humid. SW-WNW winds 5-10 mph. Temps varying from lower 70s at highest elevations to the lower 80s ( warmer south toward the Great Valley ).
**Updated Forecast Below**
Overnight Into Thursday Morning
A chance for showers. SW-WSW winds 5-10 mph, with higher gusts, on mid-upper elevation mountain ridges-plateaus. Humid & hazy. Areas of fog. Temps widespread in the 60s to near 70 degrees.
Thursday Afternoon
A good chance for showers & tropical downpours in thunderstorms. WSW-WNW winds 5-10 mph, with higher gusts, on mid-upper elevation mountain ridges-plateaus. Temperatures varying from 60s to lower 70s at highest elevations to the upper 70s to lower 80s ( warmer south into the Great Valley ).
Thursday Night Into Friday Morning
A chance of showers & thunderstorms. Areas of dense fog. Light winds. Temperatures widespread in the 60s.
Friday Afternoon
A good chance for showers & tropical downpours in thunderstorms. Light winds. Temperatures varying from 60s to lower 70s in upper elevations to the middle 70s to lower 80s ( warmer south into the Great Valley ).
Weather Discussion ( Some Changes )
It is clear now that the boundary will stall across the mountain area, with a continued any place and any time type of pattern featuring intervals of showers & tropical downpours in thunderstorms ( as somewhat drier air does work in north toward the Ohio River ).
Developing Cumulonimbus Along Outflow Boundary – August 17, 2016
For the second day out of three another line of thunderstorms moved across the Cumberland Mountains with heavy rain and booming thunder. With locally more than 2.00″ of rain falling during Monday-Wednesday ( August 15-17 ), this increases the concern for too much rain in places through coming days.
*More than a foot and one-half ( 18.00″ ) of rain has fallen in the City of Norton this summer, with locally higher amounts in the area. This also increases the potential for more rapid run-off if heavy rainfall develops or becomes prolonged in nature.
NAM 12 KM Model Total Rainfall Forecast To 8 AM Sunday – August 21, 2016
Heavy rain will be likely along a stronger cold front later Sunday into early Monday, beyond the forecast period above, such that the potential exists for hefty amounts ( at least in places ).
The Bottom Line…The mountain area will have to wait a while longer to enjoy much drier air, with a stalling boundary set to keep showers & tropical downpours in thunderstorms in the forecast into this weekend when a second, stronger cold front will finally push the high dewpoint ( muggy ) air southward early next week.
Stay tuned to NOAA Weather Radio and your favorite media sources for possible warnings and/or advisories that may be needed through coming days.
Previous Discussion
Rainbow Amid Cumulus Over Long Ridge – August 14, 2016
Weather conditions during the past few days have been straight out of “Beauty And The Beast” with a gorgeous rainbow-cumulus combination being captured over the Tennessee Valley Divide, in southern Dickenson County, by Wayne Riner on Sunday, followed by a beast of a squall line that blasted across Lee, Scott-Wise counties into Dickenson and portions of Russell-Buchanan counties on Monday PM.
Turbulent Clouds Develop In Advance Of Squall Line – August 15, 2016
Hundreds of homes lost electricity due to strong winds and lightning hits as the squall line passed. Rainfall was torrential into Lee, Scott, and Wise counties with 1.00″ to 1.50″ occurring within only 30-45 minutes from The Cedars to High Chaparral.
Wes Ward reported 0.61″ of rainfall at the City of Norton Water Plant ( 3.74″ August / 17.78″ during Summer / 39.06″ in 2016 ) as rain did diminish upon crossing the High Knob Massif ( versus double that much along the windward side of the massif ).
University Of Virginia’s College At Wise
The main corridor of thunderstorms developed over the Great Valley on Tuesday afternoon, as we now begin to enter a “any place and any time” type of pattern along a stationary boundary that tries to slip south a bit by late Thursday to reduce storm chances in the Cumberland Mountains for a short period ( with perhaps, more refreshing air being felt briefly on northerly flow ).
Daily August National Weather Service Statistics – Clintwood
While air temperatures have not been even close to those in the Great Valley, where 44 days of 90+ degree heat have been officially recorded for the Tri-Cities, high humidity levels continue to be nearly relentless in all locations.
*Mixing with breezy to gusty winds making the air along and north of the High Knob Massif feel somewhat more refreshing August 16 in wake of the vigorous Monday storms.
National Weather Service Station In Middle Elevations – Nora 4 SSE
Day-time MAXS varied from 70s above 3000 feet to the low-mid 80s across Wise & Dickenson counties ( 85 degrees in Clintwood ) on August 16 versus another blazing day ( with 95 degrees ) in the Tri-Cities of the Great Valley.
NAM 12 KM Model Total Rainfall Forecast – Tuesday AM Run
The first of two cold frontal boundaries begin to have more impact on local weather Wednesday into Thursday, with the potential for locally heavy-excessive rainfall.
NAM 12 KM Model Total Rainfall Forecast – Early Tuesday PM Run
If this first boundary can slip a little south, somewhat more refreshing air will be felt on northerly flow by Thursday PM into Friday morning.
Although I now have that in my current updated forecast, this remains to be seen and will be dependent upon the boundary’s position come Thursday afternoon-evening.
European 51-Member Ensemble MEAN 850 MB Temp Anomaly Forecast – DAYS 6-10
A more consistent trend is the arrival of much less humid air by early-middle portions of next week, in wake of the next cold front, with the biggest differences being felt by night with cooler temperatures ( especially in valleys ). Fingers crossed this trend will continue to hold.
