A strong cold front will transport a cool, early autumn air mass into the mountains by Wednesday. Unseasonably cool temps are expected through the upcoming weekend, with widespread night-time temperatures dropping into the 40s. Colder mountain valleys will fall into the 30s on coldest nights, with near freezing to even below freezing conditions not impossible amid coldest valleys at upper elevations in the High Knob Massif-Burkes Garden corridor ( with the full cooling potential dictated by sky cover and wind ).
Overnight Into Tuesday Morning
Mostly clear to partly cloudy. Breezy to gusty winds over mountain ridges. SSW-SW winds 5 to 15 mph, with higher gusts on mountain ridges-plateaus below 2700 feet. Winds SW-WSW 10-20 mph, with higher gusts, along mountain ridges above 2700 feet. Temperatures varying from 50s in sheltered valleys to the 60s on exposed ridges-plateaus. Areas of dense river valley-lake fog at low elevations.
Tuesday Afternoon
Showers & thunderstorms becoming likely. Downpours possible. SSW-WSW winds 10-20 mph, with higher gusts, along middle-upper elevation mountain ridges-plateaus. Temperatures varying from the low 60s to the lower 70s, coolest in upper elevations. Low clouds-fog forming in areas of showers-storms.
Tuesday Night Into Wednesday Morning
Showers & thunderstorms tapering to showers & drizzle. Winds shifting to NNW-NNE at 5-15 mph, with higher gusts on mid-upper elevation mountain ridges. Temperatures dropping into the 50s ( mid-upper 40s highest elevations ). Low clouds and locally dense fog becoming widespread at mid-upper elevations along and north to northwest of the High Knob Massif-Tennessee Valley Divide.
Wednesday Afternoon
Partly-mostly cloudy. Much cooler. A chance of instability showers beneath increasing cold air aloft. Light NNW-NNE winds generally less than 10 mph. Temps varying from the low-mid 50s in upper elevations to the low-mid 60s.
Wednesday Night Into Thursday Morning
Partly cloudy. Chilly. Winds NW-N at 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges. Temperatures dropping into the 40s, with 30s in colder mountain valleys. Areas of dense river valley fog.
Thursday Afternoon
Partly to mostly sunny. Cool and crisp. Winds WNW-NW at 5-10 mph, with higher gusts along mountain ridges. Temps varying from low-mid 50s to the low-mid 60s.
Thursday Night Into Friday Morning
Mostly clear to partly cloudy. Chilly. Light winds on mountain ridges ( calm wind in valleys ). Temperatures widespread in the 40s, with 30s within colder mountain valleys ( 30 to 35 degrees in the coldest valleys at upper elevations ). Areas of dense river valley and lake fog at lower elevations.
Friday Afternoon
Mostly sunny. Blue skies. Light northerly winds generally less than 10 mph. Temperatures varying from upper 50s to lower 60s in upper elevations to the upper 60s to low 70s.
Friday Night Into Saturday Morning
Mostly clear. Chilly. Large vertical temperature spread developing between colder valleys & milder ridges. Winds NNE-NE at 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges. Temperatures varying from the 30s in colder mountain valleys to low-mid 50s on exposed mountain ridges-plateaus. Locally dense river valley fog.
The approach of Major Hurricane Irma toward the southeastern USA will be the big weather story heading into this weekend, with potential impacts to the southern-central Appalachians being monitored for next week. Stay tuned for later updates.
Weather Discussion ( Autumn Chill )
Thursday Evening Update
You know the night ahead will be cold when temps in the high valleys drop into the 40s before 8:00 PM, under mainly clear skies and developing drainage flows.
AM Low Temperatures September 7, 2017
Jefferson 2 E, NC 37 degrees
Transou, NC 37 degrees
Frost, WV 39 degrees
Tazewell, VA 39 degrees
Burkes Garden, VA 41 degrees
Shady Valley, TN 41 degrees
Canaan Valley 2, WV 43 degrees
It is not just the ice box of the Big Cherry Lake basin that is getting cold, as noted by low temperatures reported across the mountain region early on September 7 ( I suspect that the Big Cherry was coldest, as later data will determine ).
Low temperatures into the morning hours of September 8 will be even colder, especially within the most favored cold places of Canaan Valley, Burkes Garden, and the Big Cherry.
National Hurricane Center Irma Track Forecast – 8 PM September 7, 2017
Meanwhile, the forecast for CAT 5 Irma continues to look ominous and extremely severe for Florida.
European 51-Member Ensemble Cluster Forecast Track At 8 AM Sept 7
Significant impacts are likely into the southern Appalachians. Stay tuned for later updates.
Tuesday Evening Irma Notes
Pressure was used to rank hurricanes from 1850 into the 1990’s before a shift to only using wind speed.
List of Strongest Atlantic Basin Hurricanes By Pressure
+Indicates strength was not continuous ( these systems fell below CAT 5 then regained that status at least once during their lives ).
Atlantic Basin Hurricane Ranks Using Wind Speed
Irma is in second place, tied with the 1935 Labor Day beast, Gilbert, and Wilma, if using wind speed alone.
Lower pressure generally = stronger winds, but not always, and total destruction and energy released is certainly often caused by more than just winds ( as Harvey exemplifies ).
It can be argued that there are many ways to rank such monsters, including death toll and total destruction. It is even more difficult to place a rank on pure misery and suffering by humans and all species of life impacted.
Previous Discussion
A mass of true autumn air will push into the mountains by Wednesday into Thursday behind the passage of a strong cold front, featuring showers & possible thunderstorms during Tuesday into early Wednesday.
High Knob Massif Webcam – University Of Virginia’s College At Wise
Following a chilly beginning to Labor Day ( Monday ), with lower 40s to lower 50s widespread in mountain valleys, an increase in low-level haze was notable into the afternoon as temperatures peaked in the middle-upper 70s from Norton-Wise to Clintwood and mid-upper 60s at high elevations in the High Knob Massif.
NAM 12 KM Model Total Rainfall Forecast
The focus now shifts to a developing eastern USA trough and strong cold front, with a true push of early autumn air into the central-southern Appalachians in coming days.
European 51-Member Ensemble Mean 850 MB Temp Anomalies: Days 1-5
For a week, or more now, this anomalous push of chilly air has been well defined and forecast by the ensemble mean of the European Model group. Only details of how cold it gets in any given place are yet to be determined, largely based upon if skies can remain clear and boundary layer winds decouple from the large-scale flow field on any night during the September 6-10 period.
It is a no brainer that colder mountain valleys will drop into the 30s at some point, the only question is if any of the infamous frost pockets can actually reach freezing or a little below ( such as those highlighted in my Summer 2017 Data section ) in days ahead.
Freezing conditions have at some point in time occurred during every month of the year within these most favored places, so it is certainly not unprecedented by any stretch to have such occur during early September ( the start of Meteorological Autumn ).
National Hurricane Center Track Forecast At 11 PM Monday – September 4, 2017
The big story in the weather world, of course, will be major hurricane Irma as it approaches the Islands and the USA.
Hurricane Irma Spaghetti Model Track Guidance
The main model cluster, as well as ensemble groups of both the GFS & European, show that there remains uncertainty with respect to track during the next week ( of course ). A major USA doomsday hit is not set in stone; although, it is also not in any way being ruled out. The main aspect at this point in time is prepare for the worst and hope for the best outcome. That includes the southern-central Appalachians.
GFS Model Mean Sea Level Forecast At 8:00 AM Sunday – September 10, 2017
The exact position varies from run to run on the models, but there is some considerable agreement, when putting all the ensembles from the European & GFS together, on a north-ward turn by this weekend. Exactly when and where that happens will then help better determine the implications.
GFS Model Mean Sea Level Forecast At 2:00 AM Tuesday – September 12, 2017
Certainly a much better handle on this setting will be had by later this week ( this is only Monday ), as part of the final outcome is going to depend upon how Irma tracks through the island chains and if she has any significant interaction with them and their mountains. Stay tuned for updates.
