ALERT For Localized Flash Flooding And Strong Thunderstorms Through Thursday (June 18-20) With Heavy-Excessive Rainfall
*Saturated ground and a slow moving weather system will combine to enhance the risk of flash flooding through Thursday (June 20). Local flash flooding rains were observed during Monday, June 17, across portions of Wise and Dickenson counties.
*Strong to severe thunderstorm development will be possible Wednesday (June 5).
Shower and thunderstorm development, with a threat of heavy rain and locally damaging winds and hail, is being monitored for Wednesday.
The threat of heavy to locally excessive rainfall is also being monitored for late week into early next week during the June 7-11 period.
Previous Headlines And Discussion
A gusty wind shift to the north will bring much cooler air into the mountains late Sunday Night into early Monday AM, with temperatures at high elevations falling into middle to upper 40s versus mid-upper 50s at lower-middle elevations. Wind chills will drop into the 30s at highest elevations.
*Update – Minimums in the 30s to lower 40s were observed within colder mountain valleys into the morning hours of June 4 (as expected).
The Mountain Empire will be on the southern fringe of unseasonably cool air, with values 10-20+ degrees below average for early June, that will be centered over the upper Great Lakes and New England during Monday into Tuesday of June 3-4.
Temperatures on Monday will be autumn-like, especially in the high country, with max readings varying from 50s to lower 60s above 3000 feet in the High Knob Massif to the upper 60s to lower 70s at lower-middle elevations (warmer to the south in the Great Valley of eastern Tennessee).
This will set the stage for chilly temperatures into Tuesday AM, with only the potential for high clouds acting to prevent readings from reaching their full cooling potential. MIN temperatures in the 30s are expected in colder mountain valleys from the High Knob Massif northeast along the Appalachians into Pennsylvania and New York where such cold temperature will become more widespread in nature. MINS in the 40s to low 50s will be common across much of the area, outside of colder mountain valleys.
Microclimate links the atmosphere, biosphere, hydrosphere-cryosphere and lithosphere together (they collectively dictate it) with a few indicator species in the High Knob Massif being Betula alleghaniensis, Viburnum lantanoides, Trillium undulatum, Maianthemum canadense, Osmundastrum cinnamomeum, Catharus fuscescens, Catharus guttatus, Cardellena canadensis, Setophaga caerulescens and Setophaga magnolia to note a few.
Having cold temperatures, and even frost, in high valleys from the High Knob Massif to Burkes Garden northeast in selected locations, known as frost pockets, through the eastern West Virginia highlands into western Maryland is nothing atypical during summer.
Dewpoints around 875-850 MB are a key factor in locations where high terrain reaches upward into this elevation zone. July 17-August 14 is the only period not to feature a night to freezing or below in Burkes Garden, which has the longest data period of any station in southwestern Virginia.
Research at the University of Virginia’s College At Wise is showing that high valleys in the High Knob Massif tend to run colder than Burkes Garden on average, but any given night may be different and Burkes Garden may be colder depending upon the cloud cover, surface conditions related to decoupling and dewpoints at upper elevations between these two Appalachian frost pocket locations.
The current terrain model forecast heading into Monday Night-Tuesday AM will be favorable for decoupling of boundary layer winds with unseasonably dry, low dewpoint air within the 900-800 MB zone. The only negative factor could be high clouds at altitudes above 25,000 to 30,000 feet in the atmosphere.
A stormy pattern with a notable above average precipitation trend, especially along the front ranges of the mountains, will develop in wake of this cool spell. This argues against unseasonable June heat and instead for muggy conditions with a positive feedback developing between surface moisture, cloudiness, and general wetness.
Weather Headlines
A reduction in heat and increase in wetness is being outlooked heading into early June, especially along the Cumberland-Allegheny and Blue Ridge mountain ranges near and north of the central valley of eastern Tennessee (the Great Appalachian Valley Province).
A cluster of strong-severe thunderstorms generated local wind damage and power outages as it blasted across southeastern Kentucky into northern Dickenson County on May 26.
A ring-of-fire pattern will begin influencing the mountain area to a much greater extent heading into early June, with a contraction of the eastern USA heat dome that has ruled the second half of May 2019. This will place the Mountain Empire in between unseasonably cool air to the north and unseasonably hot air retreating to the south.
Note how the temperature regime changes during the first week of June (from above to below).
These changes occur as the pattern deamplifies with a contraction of the eastern USA heat dome and development of a more zonal to WNW flow into the eastern USA, replacing the broad SW flow regime which has locked severe weather in place within locations across the central USA and north of the Ohio River in the second half of May 2019.
Observe how the 500 MB height pattern changes (from above to below) in the first week of June. This occurs following an initial transition period during the upcoming weekend into early next week, when cooler and drier (lower dewpoint) air is felt. The potential for unseasonably cool air to reach the local area for a period of time is on the table and will be interesting to watch as a more northerly flow field develops. Eventually, at this time of year, this type of flow will become favorable for a ring-of-fire pattern as coolest air retreats northward unless the upper troughing becomes highly anomalous (deep-persistent).
This is not breaking news, of course, as the Mountain Empire has been just south of a ring-of-fire flow during recent days.
This type of flow regime will be favorable for clusters of thunderstorms, some strong to severe, as dictated by past climatology. This occurs as the ring-of-fire is displaced south and reoriented with contraction of the northern & northeastern heat dome periphery, assuming the 51-member ensemble mean is mainly correct in progged W-NW flow field trajectories.
Anomalies observed during May intensified during the May 12-26 period to help anchor persistent storminess in the zone between height anomaly centers (below).
The majority of the 4.00″ to 6.00″ of rain that fell in the May 1-28 period from the High Knob Massif north to Clintwood was observed during the May 1-12 period, with more hit-miss action during the second half of this month.
The majority of warmest days, even at high elevations, have occurred during the past two weeks with low-mid 70s on hottest days at highest elevations within the High Knob Massif and Black Mountain (following the unseasonably chilly air mass of May 13-15).
It is not surprising that highest temperatures are occurring over the driest ground in the southeast USA, with even the typically hot Tri-Cities area of eastern Tennessee being held in check by some energy being used to evaporate soil moisture accumulated from long-term wetness.
If precipitation continues to run below average in the Tri-Cities this effect will wane as the ground continues to dry during Summer 2019, however, it will continue if the upcoming June pattern reverses short-term dryness.
*ALERT For The Potential Of Strong To Severe Thunderstorm Development During Sunday Afternoon And Sunday Night ( May 26, 2019 )
A Severe Thunderstorm Watch is in effect for locations near & west of the Virginia-Kentucky stateline into Sunday evening (the Watch may need to be expanded and/or warnings may be issued…….stay tuned to NOAA Weather Radio and your favorite media sources for updates).
A cluster of strong-severe thunderstorms is developing along the periphery of high pressure, with hot air, in a ring-of-fire type of pattern. The main severe threats are wind damage, hail, dangerous lightning and torrential downpours of rain.
Interactive Full Screen Doppler Radar
RealEarth from the University Of Wisconsin-Madison now has real-time lightning tracking and many other features here: RealEarth Interactive Display System
Stay tuned to NOAA Weather Radio and your favorite media sources for updates and possible warnings which may be needed.
Observed Weather Conditions
Frosty cold conditions greeting many mountain valleys across the central-southern Appalachians into morning hours of Wednesday, May 15, with a few specific minimum temperatures including:
Big Cherry Valley: 29 degrees
Burkes Garden: 30 degrees
Frost 3 NE, WV: 30 degrees
Jefferson, NC: 31 degrees
Beckley, WV: 32 degrees
Boone, NC: 32 degrees
Hacker Valley, WV: 32 degrees
Shady Valley, TN: 32 degrees
Transou, NC: 33 degrees
Lewisburg, WV: 33 degrees
Bayard, WV: 34 degrees
Radford: 34 degrees
Bluefield, WV: 34 degrees
Buckeye, WV: 35 degrees
Clintwood 1 W: 36 degrees
Galax: 36 degrees
Sandyville, WV: 36 degrees
White Sulpur Springs, WV: 36 degrees
Since frost typically forms at ground level when official air temperatures, at 5-6 feet above ground level, reach 36 degrees, I have listed sites with min temperatures at or below the 36 degree threshold.
Locations not in Virginia have the state identifier included.
Thursday morning, May 16, also featured scattered frost in coldest mountain valleys with temperatures dropping into the middle 30s.
Looking Forward_Warm Pattern
Above average temperatures are now looking like they will dominate the remaining days of May 2019, with more ensembles of the 51-member European Model cluster coming into agreement.
A southwesterly flow aloft is now being predicted to intensify into next week (see 6-10 day period below for the May 22-26 period).
Although a general below average precipitation regime is forecast, locally heavy showers and downpours in thunderstorms will occasionally be possible with day to day chances being dictated by not only upper air waves but surface outflow boundaries and instability. A main focus of strong-severe thunderstorms will tend to move around the periphery of sinking air aloft, with clusters of storms rotating around the outer edges of heat to the west and north of the Mountain Empire…eventually this will change, so stay tuned for later updates.
Weather Headlines
A beautiful array of orographic clouds capping the High Knob Massif, which contributed to heavy weekend rains, lingered into Monday morning as seen from our weather research webcam at UVA-Wise.
Unseasonably cool conditions will continue with widespread 30s at elevations above 3000-3500 feet, amid abundant clouds on upsloping NW winds, into Tuesday morning. The coldest air temperatures in mountain valleys are expected Wednesday morning when mostly clear skies and light winds will support low-mid 30s (30 to 35 degrees) in colder valleys at middle-upper elevations.
Two different atmospheric settings will generate these cold temperatures, with cold air advection (transport) + adiabatic upslope cooling working to generate 30s at upper elevations into Tuesday morning as cloud bases lower (the freezing level will drop to around 4800-5000 feet such that highest peaks on the windward facing side of highest mountains could form a little rime) versus more classic cold air drainage + radiational cooling under clear skies, light winds, and low dewpoint air that will support cold mountain valley conditions into Wednesday morning (allowing Appalachian frost pocket locations, which are capable of dropping into the 30s or even below freezing during any month of the year, to realize their potential). High mountain ridges will tend to be coldest into Tuesday AM versus high mountain valleys on Wednesday AM.
Monday felt like winter in the high country of the High Knob Massif as low-mid 40s combined with low clouds and gusty NW winds to generate wind chills as cold as 30 to 35 degrees into the afternoon hours of May 13. Ditto for the summit level of Black Mountain.
For those keeping track, this is not surprisingly part of a repetitive Spring 2019 pattern that will feature another surge of warmth, with showers and thunderstorms by late this week into early next week, that is again followed by another cool surge toward the middle of next week. That is the current trend, and given this repetitive pattern it has better than even odds of verification, although, sooner or later this cycle will be broken and conditions which can be called summer will finally set up shop with less radical temperature fluctuations in the mean.
The latest rain event boosted 2019 totals to between 32.00″ and 33.00″ in the City of Norton, at the northern base of the High Knob Massif, and to between 35.00″ and 40.00″ within wetter locations at upper elevations in the massif (15.00 to 18.00″+ during Meteorological Spring).
Alert For High Water Levels
*A general 2.00″ to 4.00″ of rain has fallen along a line extending from Natural Tunnel State Park in Scott County to the City of Norton in Wise County and Council in southern Buchanan County, with 3.50″ to 4.00″ maximum totals in the High Knob Massif, as of early afternoon Sunday (May 12), along a Big Cherry Lake to Guest River Gorge corridor.
Roaring water and dangerously high levels are occurring on creeks draining the high terrain. Extreme caution is advised through the remainder of Sunday into early Monday. Strong rises are also occurring on the Clinch River, but it is expected to remain below flood stage.
The good news, following a weekend spent amid clouds above 3000 feet, is that the bulk of heavy rains have now passed. While another shower or local thunderstorm can not be ruled out, the focus now is on much drier air expected to overspread the mountains by Monday into Tuesday with seasonally cool conditions.
*Increasing showers and downpours in thunderstorms will begin to impact the mountain region in coming days, with the Friday-Sunday period of May 10-12 featuring an approaching frontal boundary that slows down across the Appalachians. Hit-miss activity Thursday will become more widespread in nature Friday afternoon into Saturday-Sunday as a upper wave interacts with the surface boundary.
A southwesterly upper air flow (above) ahead of a upper air trough will support occasional waves of showers & thunderstorms through this weekend. Air will turn cooler Saturday as the surface boundary temporarily passes south of the Cumberland Mountains and the low level flow turns northerly, with upslope flow and lowering clouds. A wave of low pressure will then enhance showers-thunderstorms on Mother’s Day (Sunday, May 12).
Heavy to locally excessive rainfall amounts will be possible through this weekend in advance of a much cooler, drier air mass currently expected to overspread the Appalachians by early next week. Those living along streams and in typically flood prone, poor drainage locations will need to monitor the possibility for rapid water level rises through this weekend.
Widespread 1.50″ to 3.50″ rainfall amounts from the Clinch River Valley of Scott County northward across the High Knob Massif into Dickenson County during May 2-5, combined with long-term antecedent wetness, sets the stage for potential high water concerns given additional heavy to locally excessive rainfall amounts upcoming through this weekend.
*Much cooler and drier air is currently expected to overspread the area during Monday into Tuesday of May 13-14, although cooler air will be noted Saturday on upsloping northerly air flow behind initial passage of a surface cold frontal boundary, which stalls, then lifts back northward across the region during Sunday.
A trough (above) in the upper air will replace upper air ridging aloft and be accompanied by much cooler, drier air (below) by May 13-14.
*The potential for air to become cold enough to support frost and near to below freezing temperatures, especially within typically colder mountain valleys away from major rivers and lakes, is being monitored for early next week.
This is not surprising, with minimum temperatures dropping into the 30s to low 40s within colder mountain valleys into morning hours of May 7 and into the 40s during May 8.
For more information reference: Spring 2019_High Knob Massif Area
Overnight Into Thursday Morning
Partly to mostly clear. Seasonally mild. Winds SE-S at 5-15 mph, with higher gusts, on mountain ridges and plateaus below 2700 feet. Winds S-SSW at 10-20 mph, with higher gusts, on mountain ridges above 2700 feet. Temperatures varying from low-middle 50s in cooler mountain valleys to 60s on exposed middle elevation ridges and plateaus.
Thursday Afternoon
Partly cloudy with a chance of hit-miss showers and thunderstorms. Winds S-SW at 5-15 mph with higher gusts on mountain ridges & plateaus. Temps varying from upper 60s to lower 70s at upper elevations to the upper 70s to lower 80s (locally warmer within downslope locations of northern Wise-Dickenson and Buchanan counties).
Thursday Night Into Friday Morning
Chance of local evening showers & thunderstorms, then mostly cloudy and mild. Winds S to SSW 5-10 mph, with higher gusts, along mountain ridges & plateaus below 2700 feet. Winds SSW to WSW at 10-25 mph, with higher gusts, mountain ridges above 2700 feet. Temperatures in the upper 50s to middle 60s. Local areas of fog (especially where rain fell).
Friday Afternoon
A chance of showers and thunderstorms. Local downpours. Any storm could be strong to locally severe. Winds SW 5-10 mph, higher gusts possible around thunderstorms. Temperatures varying from mid 60s to around 70 at upper elevations to the mid 70s to lower 80s (warmest lower elevations).
Friday Night Into Saturday Morning
Showers & thunderstorms becoming likely. Local downpours possible. Winds becoming northerly at generally less than 10 mph. Cloud bases dropping across upper elevations and into middle elevations between 2500-3000 feet in locations along and north of the High Knob Massif-Tennessee Valley Divide. Temperatures varying from low 50s to low 60s.
Saturday Morning Through The Afternoon
Showers and a chance for thunderstorms. Local downpours possible. Winds becoming light and variable in direction with elevation. Areas of fog, widespread at upper elevations. Temperatures in the 50s to mid-upper 60s (warmer south into the Great Valley and Tri-Cities).
Intervals of showers and downpours in thunderstorms are expected during the weekend. Locally heavy rainfall amounts will be possible, especially in advance of an upper air trough axis by late in the weekend.
