The Potential For The First Widespread Frost-Freeze Of The Season Is Being Monitored For Next Week With An Autumn Air Mass Pushing Into The Appalachians
Although numerous frosty mornings have already been observed in mountain valleys, with local sub-freezing temperatures as well, no widespread frost-freeze has yet been experienced. River valleys that fog up, and a few favored mid-elevation thermal belts, might still be able to remain above freezing. This may be progressive and not long-lived, with above average temperatures returning by late next week into the following week by day. Nights look to continue to be cold, especially in valleys, with large diurnal temp ranges.
Areas of dense fog developing in lower-middle elevations. Becoming mostly clear in the upper elevations. Light winds, except W-NW at 5-10 mph, with some higher gusts, on upper elevation mountain ridges. Temperatures varying from 30s to mid 40s in colder valleys at upper elevations in the high country of the High Knob Massif to the lower-middle 50s.
*NOTE – Temperatures Thursday will be cooler than currently in my forecast if a low-level cloud deck develops and does not mix out as currently expected. That remains a small possibility to be noted, especially in locations along & west-northwest of the Tennessee Valley Divide and High Knob Massif.
Partly to mostly sunny. Deep blue skies above any clouds. Generally light winds. Temperatures varying from low-mid 60s in upper elevations to the low-mid 70s ( warmer in river valleys, especially southward into eastern Tennessee ).
Thursday Night Into Friday Morning
Partly to mostly clear. Areas of dense valley fog. Light valley winds. Winds SE-S at 5-15 mph, with higher gusts, along middle-upper elevation mountain ridges. Large temp spread between cooler valleys and milder mountain ridges, varying from 40s to lower 50s in cooler valleys to the lower-middle 60s on exposed ridges-plateaus.
Partly cloudy. Winds SSE-SSW at 5-10 mph with some higher gusts. Temperatures varying from 60s in upper elevations to the mid-upper 70s.
Friday Night Into Saturday Morning
Partly to mostly clear. Areas of dense valley fog. Light valley winds. Winds S-SW at 5-10 mph, with some higher gusts, along mid-upper elevation mountain ridges. Large vertical temperature spread between cooler valleys and exposed ridges-plateaus. Temperatures varying from the 40s in colder mountain valleys to the upper 50s to low 60s.
Weather Discussion ( Air Mass Changes )
An unseasonably humid air mass following remnants of Nate have been ruling the mountain landscape during recent days. This is going to change, with one transition into Thursday and a much bigger change into next week.
Wednesday afternoon maximums varied from upper 60s in the High Knob Massif to the upper 70s ( 79 degrees in Clintwood ) to around 80 degrees.
October 1-10 Rainfall
Nora 4 SSE 1.48″
Clintwood 1 W 2.06″
*City of Norton WP 2.74″
Big Cherry Dam 3.60″
Robinson Knob 4.69″
*Precipitation total of 50.56″ during 2017. Upper Elevations in the High Knob Massif have had a general 55.00″ to 60.00″+ this year.
Recent rainfall was welcomed, despite bad timing for the final leg of the Cloudsplitter 100 Mile race, with current totals being nearly as great or greater than observed in September ( Norton measured 2.86″ of September rain ).
Although a notable cool push of air will be felt next week, the ensemble mean of the European Model group currently suggests it will be progressive with a trend back toward above average temperatures by later next week. The main difference versus this recent pattern being a continuation of cold nights, especially in mountain valleys, with large vertical and diurnal temperature spreads.
ALERT For Strong Winds & Heavy Rainfall Developing Sunday Into Monday Morning With Remnants of Nate
Strong Rises On Mountain Streams Will Become Possible By Sunday Night Into Monday Morning
Remnants of Hurricane Nate will begin impacting the mountain region Saturday Night into Sunday Morning with developing rain. Rainfall will become heavy during Sunday into Monday Morning, especially along windward slopes & crestlines of major orographic features like the High Knob Massif.
Reference My October 7-8 Race Forecast For More Detailed Information On The High Knob Hellbender 10K and The Cloudsplitter 100 Races.
Overnight Into Saturday Morning
Partly-mostly clear ( some high clouds ). Becoming gusty higher elevations. SSE-SSW winds increasing to 10-20 mph, with higher gusts, on middle to upper elevation mountain ridges. Temps varying from 40s in cooler mountain valleys ( sheltered from winds ) to middle-upper 50s to around 60 degrees on exposed mountain ridges and plateaus.
Becoming partly to mostly cloudy & more humid. Winds SSE-SSW at 10-20 mph, with higher gusts. Temperatures varying from upper 60s to lower 70s ( 18 to 22 Celsius ) in upper elevations, above 3000 feet, to middle-upper 70s ( 24-26 Celsius ) at elevations below 3000 feet. Warmest at low elevations in the Hanging Rock Recreation Area where temperatures could rise above 80 degrees ( 27 Celsius ).
Saturday Night Into Sunday Morning
Becoming cloudy with light rain developing overnight into morning. Cloud bases lowering to near or below the summit level of the High Knob Massif. SSE-S winds 5-15 mph below 2700 feet. Winds S-SW 10-25 mph, with higher gusts, above 2700 feet ( especially on mountain ridges ). Temperatures falling into the 60s ( 16-18 Celsius ).
Sunday Morning Through The Afternoon
Increasing rain, with a chance for thunderstorms. Locally heavy rainfall likely, especially along windward slopes and crestlines of the High Knob Massif. Lesser rain amounts in downslope locales in central-northern Wise and Dickenson-Buchanan counties.
Winds SE-SSE at 10-25 mph, with higher gusts in upper elevations ( lighter winds at lower elevations in hollows-valleys ). Temps near steady in low-mid 60s ( 16-18 Celsius ) at high elevations and in the upper 60s to middle 70s ( 20-22 Celsius ) at lower elevations ( below 2000 feet ).
Sunday Night Into Monday Morning
Rain becoming heavy. A chance of thunderstorms. Windy. Dense fog ( orographic clouds ) across upper elevations in the High Knob Massif. SE-S winds 15-25 mph, with higher gusts below 2700 feet. SSE to SSW winds 25-35 mph, with gusts over 50 mph, at elevations above 2700 feet. Temps widespread in the 60s ( low-mid 60s in upper elevations ).
Weather Discussion ( Nate & Races )
The recent streak of dry conditions will be ending this weekend, perhaps in a big way for some locations. The timing will favor the High Knob Hellbender 10K Race and the first day of the Cloudsplitter 100 races; however, the second day of the Cloudspitter will be a different story featuring deteriorating conditions.
Increasing wind and rain with Nate will not greatly impact trees at the summit level, where many trees are now bare around High Knob Lookout ( for example ), but color that is now approaching peak in other places of the high country could be hurt ( dulled and many downed ) by this system.
As of the early overnight period of Saturday, Nate is under-going expansion and increasing organization. Meanwhile, a cold frontal zone to the west has triggered a squall line to form from Texas across Oklahoma into Kansas.
Local conditions are already beginning to change, with a notable increase in both wind speeds and moisture levels across high elevations to strengthen a nocturnal temp inversion ( with cooler valleys & milder mountain ridges ).
An increase in wind speeds and rise in dewpoints have occurred at highest elevations between 9:40 PM Friday and 1:40 AM Saturday.
This will set the stage for a more humid, mild Saturday with nocturnal mountain valley inversions mixing out following sunrise. If the above trend continues, then some low clouds could begin developing above the mountain summits prior to Saturday afternoon ( when my forecast is calling for the conditions to become partly-mostly cloudy ).
Since Nate has now become a hurricane ( as of 2:00 AM ) the next 12-18 hours will be critical as to how strong he can get before landfall. A stronger Nate = a likely stronger system post-landfall which will be important to impacts across the southern-central Appalachians. Stay tuned for updates.
An Autumn Cold Front And Developing Tropical System Are Being Monitored For Possible Impacts Upon The Mountain Region By Later This Weekend Into Early Next Week ( October 8-10 )
Details on this setup are yet to be worked out, with the Tuesday night run of the operational European Model trending east to keep significant rains along and east of the mountains ( from the Blue Ridge east to southeast ). This is in contrast to the U.S. GFS Model, and most hurricane models, which track the tropical system much farther west. Timing of an approaching cold front and upper air trough will help determine where the tropical system goes and how any linkage between it and the frontal zone develops.
A shot of unseasonably cool air will likely follow whatever happens with this tropical system by the middle of next week. Stay tuned for updates.
Overnight Into Wednesday Morning
Mostly clear. Light winds, except SSE-SSW at 5-10 mph, with some higher gusts, on mid-upper elevation mountain ridges. Large vertical temperature spread between colder mountain valleys and milder ridges. Temperatures varying from upper 20s to middle 30s in colder valleys to the upper 40s to lower-middle 50s on exposed ridges-plateaus. Areas of fog along major rivers.
Mostly sunny. Light winds. Temperatures varying from mid-upper 60s in upper elevations to the mid-upper 70s. Warmer south into the Great Valley and river valleys.
Wednesday Night Into Thursday Morning
Mostly clear. Light winds. Large vertical temperature spread between colder mountain valleys and exposed ridges and plateaus. Temps varying from 30s in the colder valleys to the lower-middle 50s on exposed ridges-plateaus. Areas of river valley fog.
Mostly sunny ( some high clouds ). Light northerly winds. Temperatures varying from 60s in upper elevations to the mid-upper 70s ( warmer south into the Great Valley ).
Thursday Night Into Friday Morning
Mostly clear. Light winds. Large vertical temperature spread between colder valleys and exposed mountain ridges and plateaus. Temperatures varying from 30s to lower 40s in colder mountain valleys to the low-mid 50s on exposed ridges and plateaus.
Partly-mostly sunny ( high clouds ). Unseasonably warm. Light southerly winds. Temperatures varying from upper 60s to lower 70s in upper elevations to the upper 70s to lower 80s ( warmer south into the Great Valley ).
Friday Night Into Saturday Morning
Partly-mostly clear ( high clouds possible ). Becoming gusty higher elevations. SSE-SSW winds increasing to 10-20 mph, with higher gusts, into the overnight-morning. Temps from 40s in cooler mountain valleys ( sheltered from winds ) to mid-upper 50s to around 60 degrees on exposed middle-upper elevation mountain ridges and plateaus.
The first full moon closest to the Autumnal Equinox is always called the Harvest Moon, for times when farmers and Native Americans used moonlight to gather in late season crops. Although not quite full yet, the moon early on October 4 was getting close in the chilly air filling mountain valleys of the Cumberland Mountains.
While it is looking to be unseasonably warm and continued dry for the High Knob Hellbender 10K race on Saturday, the second day of the Cloudsplitter 100 is more uncertain and will depend upon what happens with a developing tropical system in the Gulf of Mexico.
Ensembles of the GFS Model have been farther west than the mean of the 51-Member European Model group. Right now the bulk of hurricane models are also farther west.
I think the setting will become more clear once hurricane hunter data and other data being collected gets put into the models during the next couple of days. A track like above would tend to spread heavy rain across all of the southern-central Appalachians, while a track like the current run of the Operational European Model would keep heavier rains mainly along and east of the Blue Ridge.
An ALERT For Cold Night-time Conditions In Mountain Valleys Continues, With Large Vertical Temperature Spreads Between Ridges & Valleys
While foggy river valleys and exposed mountain ridges-plateaus will remain well above freezing, a very dry air mass will continue to support both large diurnal temperature spreads and also large vertical differences between ridges and mountain valleys.
Colder valleys will continue to drop into the 30s, with local below freezing conditions expected through mid-week ( Wednesday AM of October 4 ). Reference observed minimums reported along the Appalachians on Sunday AM of October 1 in my discussion below.
Overnight Into Monday Morning
Partly to mostly clear ( high clouds ). Breezy to gusty SE winds of 10-20 mph, with higher gusts, through early to mid-overnight on mid-upper elevation mountain ridges before decreasing during the predawn. Large vertical temp spread between colder valleys and milder ridges-exposed plateaus. Temps varying from 30s in colder valleys to the mid-upper 40s to around 50 degrees on exposed ridges and plateaus ( except for a rapid temperature drop to around or below freezing in high valleys during the predawn-early morning ). Local areas of dense river valley fog along major rivers. Wind chills in the upper 30s to lower 40s in gusts along high mountain crest lines.
Partly sunny ( high clouds ). Light SE to SSE winds. Temperatures varying from low-mid 60s in upper elevations to the low-mid 70s.
Monday Night Into Tuesday Morning
Partly-mostly clear ( high clouds ). Light winds, except SSE-SSW at 5-10 mph on mid-upper elevation mountain ridges. Large vertical temperature spread between colder valleys and milder mountain ridges. Temperatures varying from upper 20s to upper 30s in mountain valleys to the upper 40s to lower 50s along mountain ridges-exposed plateaus. Fog along major river valleys.
Mostly sunny ( some high clouds possible ). Generally light winds. Temperatures varying from low-mid 60s in upper elevations to the lower-middle 70s.
Tuesday Night Into Wednesday Morning
Mostly clear. Light winds, except SSE-SSW at 5-10 mph, with some higher gusts, on mid-upper elevation mountain ridges. Large vertical temperature spread between colder mountain valleys and milder ridges. Temperatures varying from 20s to middle 30s in colder valleys to the upper 40s to lower 50s on exposed ridges-plateaus. Areas of fog along major rivers.
Weather Discussion ( WxDiversity )
Autumn has arrived in the mountains. This combined with a recent streak of dryness will enhance diversity in weather conditions, both from day-to-night and also ( as typical of this time of year in the mountains ) between ridges-valleys.
The following temperatures are mostly NWS Cooperative sites, with a few Weatherbugs added ( note Weatherbug sensors are typically mounted much higher than the standard 4-6 feet height of official thermometers ).
Western North Carolina Jefferson: 31 degrees Boone: 35 degrees Spruce Pine 4 ENE: 39 degrees
West Virginia Bartow: 29 degrees Hacker Valley: 31 degrees Frost 3 ENE: 32 degrees White Sulphur Springs: 32 degrees Lewisburg: 33 degrees Beckley: 34 degrees
Areas of valley frost were widespread across Wise and Dickenson counties, away from river valley fog, early October 1 and no doubt were also in many other places located within the mountains. Coldest high valley sites, outside of Burkes Garden, of Canaan Valley and the Big Cherry Basin in the High Knob Massif are not even yet included in this list ( that data yet to be collected ).
Valley frost is typically observed when air temperatures at standard NWS sensor height of around 5 feet reach the middle 30s since air temperatures right at ground level are generally colder. Frost occurred in the Clintwood area, for example, with a MIN air temperature of 34.8 degrees at the 5 foot sensor height.
Another interesting feature is wind chills along the high mountain crest lines. This is being caused by a compression of thicknesses by night + a pressure gradient around a High currently centered over Pennsylvania.
If anyone doubts that nocturnal wind chills are a factor, then just drive up to the High Knob Lookout and that doubt will be quickly eradicated. Winds relax into the day as thicknesses increase.
This type of setting is not ideal for coldest conditions in the higher mountain valleys; however, a relaxation during pre-dawn and sunrise periods is enough to allow for rapid temp drops in the favored frost pockets ( where temps often drop below surface dewpoints reported at any given time ).
Wind chills in the upper 30s to lower 40s are being observed along high mountain crest lines, especially in the frequent gusts. This low-level jet setting weakened into morning hours of October 1 and will likely weaken again into this morning ( October 2 ).
If the High center slides a little more southwest, allowing the nocturnal pressure gradient to weaken, conditions will actually become more favorable for cooling within the high mountain valleys into Tuesday and Wednesday mornings. Therefore, I have continued the alert for cold nights since no official advisories have been issued.
While there is little to no chance of rain this week, there are signs of important changes ahead that could break this dry streak out in the 5-10 day period ( below ) as eastern USA ridging ( above ) breaks down.
Meanwhile, it will be wise to avoid any outdoor burning.