An Alert For Dense Fog Is In Effect For Elevations Above 2600 to 3000 Feet Within The Cumberland Mountains Through 10:00 AM Saturday
Cooling air on northerly upslope flow in the wake of widespread, heavy rains will allow cloud bases to remain low through morning hours of Saturday. Caution is advised for those traveling at higher elevations overnight into Saturday morning.
The Storm Prediction Center Has Issued A Marginal To Slight Risk For Severe Thunderstorm Development On Thursday Into Friday ( July 27-28 )
Locally Heavy To Excessive Rainfall Will Be Possible Thursday Into Friday Ahead Of A Strong Cold Front That Could Lead To Local High Water Problems
Overnight Into Thursday Morning
Increasing high clouds. Hazy & humid. Areas of valley fog. Winds SSW-WSW 5-15 mph, with higher gusts, along mid-upper elevation mountain ridges. Temperatures varying from low-mid 60s to around 70 degrees.
Thursday Morning Through The Afternoon
Showers & downpours in thunderstorms developing in a hit-miss fashion. Some storms could be strong to locally severe. SW winds 5-10 mph, with higher gusts. Temps varying from upper 60s to lower 70s in upper elevations to the upper 70s to lower 80s ( warmer south toward the Tri-Cities ).
Thursday Night Into Friday Morning
A chance of showers & thunderstorms. Downpours possible. Winds S-SW 5-10 mph, with higher gusts. Hazy, humid with areas of fog. Warm with temperatures in the 60s to low 70s.
Friday Morning Through The Afternoon
Showers & downpours in thunderstorms becoming likely. Some storms could be strong to locally severe. Winds S-SW 5-15 mph, with higher gusts at elevations below 2700 feet. Winds SW to W 10-20 mph, with higher gusts, at elevations above 2700-3000 feet. Temperatures in the 60s to low 70s. Low cloud bases with dense fog at upper elevations.
Friday Night Into Saturday Morning
Rain showers. Turning cooler. Winds shifting NNW-NNE at 5 to 15 mph, with higher gusts. Temperatures dropping into the 50s to low-mid 60s ( coolest at highest elevations ). Low clouds with dense fog at higher elevations.
Saturday Morning Through The Afternoon
Morning showers ending with low cloud bases lifting into afternoon. Skies becoming partly to mostly cloudy. Winds NNW to NNE at 5 to 15 mph, with some higher gusts along mountain ridges. Temperatures varying from upper 50s to lower 60s at highest elevations to the upper 60s to lower 70s ( warmer south into the Great Valley ).
Low temperatures are expected to fall into the 40s to low-mid 50s into Sunday morning ( coolest within higher mountain valleys ).
The coldest mountain valleys at upper elevations, from the High Knob Massif to Burkes Garden, are expected to drop into the 40 to 45 degree range on both Sunday and Morning mornings, with an increasingly large vertical temperature spread expected by early Monday as exposed ridges fall only into the upper 50s to low 60s. If cooling conditions are perfect, coldest spots may dip just below 40 degrees as most recently observed on June 28.
Weather Discussion ( Cold Front )
A strong cold front for late summer is the main focus of this weather period, with a major air mass transition occurring during the weekend.
Air temps will hold in the 50s on highest peaks from the High Knob Massif to Mount Rogers during the day Saturday ( illustrating the early autumn-like nature of this upcoming air mass change ).
Some orographic forcing will develop as this cold front approaches, with potential to off-set the general trend of dryness observed during the past 30-60 days.
Although November-April is the prime orographic forcing season, with October & May often being months of transition, when large-scale storm systems develop pressure gradients that push upon the mountain terrain ( the mountains “push back” and generate torques on the atmosphere ), orographic forcing settings can and occasionally do develop during the convective season.
Heavy to excessive rains to the north, with rising air from Ohio to Wisconsin, has aided summer dryness across much of Virginia, SE Kentucky, northeastern Tennessee and portions of North Carolina where air has been sinking by compensation ( couplets of rising-sinking air are common on both local and synoptic scales during the convective season, often dictating patterns of summer rain ).
This general pattern has been superimposed upon local dry-wet feedbacks, favoring large rainfall variations over short distances.
Measured Rainfall Since June 1
Clintwood 1 W: 5.94″ ( -2.83″ below 1981-2010 average )
Nora 4 SSE: 10.23″ ( Near To Above Average )
Summer 2017 rainfall has varied dramatically across Dickenson County, for example, with about twice as much falling upon Long Ridge of Sandy Ridge as in Clintwood since the beginning of June.
Although more summer certainly lies ahead, recent heat will be broken and a near to below average temperature pattern is currently predicted by the European ensemble MEAN during the next 5-10 days into early August.
Partly-mostly clear. Areas of valley fog. Light winds. Temperatures varying from mid-upper 50s to lower 60s within cooler valleys to the middle-upper 60s.
Partly to mostly cloudy skies. A chance of hit-miss showers and thunderstorms. Light winds. Temps varying from the 70s in upper elevations to the mid-upper 80s.
Tuesday Night Into Wednesday Morning
Chance of a hit-miss evening shower or thunderstorm. Hazy and humid with areas of valley fog. Light SSW to W winds generally less than 10 mph on mid-upper elevation mountain ridges. Temps in the 60s to near 70 degrees.
Partly-mostly cloudy skies. Hazy-humid. A chance of hit-miss showers and thunderstorms. WNW-NW winds 5-10 mph, with higher gusts ( especially on mountain ridges ). Temperatures varying from 70s in upper elevations to the mid-upper 80s.
Wednesday Night Into Thursday Morning
Warm & humid. A chance of hit-miss showers & thunder-storms. NW-NNW winds 5-15 mph, with higher gusts, on middle-upper elevation mountain ridges-plateaus. Temps in the 60s to lower 70s.
Partly-mostly cloudy skies. Hazy & humid. A chance of hit-miss showers & thunderstorms. Winds NW-NNW 5-10 mph. Temperatures varying from 70s in upper elevations to the mid-upper 80s ( warmer, as per each day, at low elevations south of the High Knob Massif and in the eastern Kentucky foothills and lower sections of the Russell Fork-Levisa Fork river valleys around Haysi and Grundy ).
Weather Discussion ( Dog Days )
The somewhat lower humidity of recent days is being replaced by a more humid air mass, with a dominant and deep NW-N flow regime aloft developing around a large heat dome centered over the central USA.
The afternoon MAX reached 70 to 74 degrees at highest elevations in the High Knob Massif on Saturday, July 15, as relatively pleasant weekend conditions were observed in the high country ( nocturnal low temps dropped to 50-55 degrees within high valleys ).
To the south, by contrast, weekend conditions remained hot in the Great Valley with upper 80s to lower 90s reported from Knoxville into the Tri-Cities.
Rainfall has been hit or miss during the past week, with a notable dry trend since the start of Meteorological Summer ( on June 1 ) across much of the Cumberland Mountains, at least relative to what is average for this time of year.
Note heavy, locally excessive, rains to the north across Indiana and Ohio as thunderstorm clusters moved around the periphery of heat last week. Rain was locally heavy across Dickenson-Buchanan counties & adjoining locales in eastern Kentucky and southern West Virginia as a front passed during the July 13-14 period.
Although 1.25″ of rain fell in Clintwood during July 14, only 5.26″ have been measured since June 1 ( 2.14″ below the 1981-2010 avg. ), which is also about the same as observed at Big Cherry Lake Dam. A total of 7.68″ have been measured at Nora 4 SSE on Long Ridge of Sandy Ridge, in between these two sites, to illustrate the hit-miss nature of Summer 2017 convection.
A upper low over central Virginia-North Carolina will be pushed eastward as the heat dome initially expands, with deep NW-N flow aloft that may carry debris cloudiness from thunderstorm clusters forming on the periphery of blazing heat over the Upper Midwest.
A hit-miss pattern of convective activity is expected to continue as heat builds through the remainder of this work week. Changes will be possible by this weekend into next week, especially, as troughing develops aloft and monsoon moisture continues to flow around the big heat dome.
An increasing potential for showers-thunderstorms will occur over time with a retrogression of the heat dome core, especially by later this weekend into next week ( this is the current ensemble trend ). Stay tuned for updates.
1 ). A Mesoscale Convective System will drop south to southeast toward the mountains Friday Night into the early hours of Saturday. While a weakening trend is expected, strong to locally severe thunderstorms will remain possible as this cluster of storms approaches the Cumberland Mountains.
The main storm threats are damaging winds, lightning and heavy rainfall. This system is expected to weaken across the higher mountain terrain overnight.
2 ). Rain cooled outflow from this system & approach of a surface cold front will trigger new development from the morning into afternoon hours of Saturday.
An outflow boundary just north of Jackson, Ky., at 9:27 PM is starting to move out ahead of the MCS, indicating a trend toward weakening during coming hours. Any left-over boundaries + the surface front will bear watching for new development following onset of day-time heating Saturday.
3 ). Drier, less humid and more stable air is expected to overspread the mountains from northwest toward southeast by late Saturday afternoon into Sunday.
Lower dewpoints will make conditions feel much better from Saturday Night through Sunday Night, with notable cooling within mountain valleys ( MINS in the 50s will be widespread across the area, with coolest valleys dropping into the 40s to contrast with upper 50s to low-mid 60s on exposed mountain ridges Sunday & Monday mornings ).
4 ). A ring-of-fire pattern will become possible next week around the periphery of a building heat dome with rising day-time temperatures early next week.
A modeling trend ( ensemble mean ) is for a heat dome to set up near the Red River Valley & Texas-Oklahoma panhandles next week. This will generate a WNW-NW flow pattern and ring-of-fire convective regime ( i.e., clusters of showers and thunderstorms will develop along the edge of the hottest air and move around the periphery of the heat dome ).
The eventual location of the heat dome core will need to be followed, along with the recent dry feedback tendency that has generated below average rainfall across portions of the mountain region during June-early July ( local wet feedback has also been observed as typical of patterns featuring hit-miss convective development & movement ).