051817 Forecast

Mountain Area Forecast ( May 18-21 )

ALERT For Showers & Thunderstorms With A Heavy Rainfall Potential Into Sunday And Sunday Night 

A high water content air mass will set the stage for heavy rainfall as a upper air trough & surface cold front approach the mountains Sunday.  Remain alert for strong rises along streams and for possible high water issues.  Stay tuned to NOAA Weather Radio and your favorite media sources for possible watches and/or warnings which may be needed.

The Storm Prediction Center Has Issued A Marginal Risk Of Severe Thunderstorms Into Sunday Morning

( Former Alerts )

The Storm Prediction Center Has Issued A Marginal Risk Of Severe Thunderstorm Development During Friday And Friday Night

Tonight Into Friday Morning

Partly cloudy.  A chance of showers & thunderstorms by overnight into morning.  Downpours possible.  Winds SSW to WSW 5-15 mph, with higher gusts, along middle-upper elevation mountain ridges and plateaus.  Mild with temps dropping into the 50s ( coolest valleys ) to middle 60s.

Friday Morning Through The Afternoon

A chance of showers & downpours in thunderstorms.  Some storms could be strong to locally severe.  Winds SSW-WSW at 5-15 mph with some higher gusts.  Temperatures varying from the 60s to mid-upper 70s ( coolest highest elevations ).

Friday Night Into Saturday Morning

Partly-mostly cloudy.  Areas of fog.  Chance of a hit-miss shower or thunderstorm.  Light winds.  Temperatures from the 50s to lower-middle 60s ( coolest in mountain valleys ).

Saturday Afternoon

Partly sunny.  Unseasonably warm with a chance for hit-miss showers or thunderstorms.  Local downpours possible.  SSE-S winds at 5-10 mph with higher gusts.  Temps varying from 70s in the upper elevations to the mid-upper 80s.

Saturday Night Into Sunday Morning

Partly cloudy.  A chance of showers and downpours in thunderstorms, especially toward morning.  Winds SSE-SSW 5-15 mph, with higher gusts.  Temperatures varying from the upper 50s to lower-middle 60s.

Sunday Morning Through Sunday Afternoon

Periods of showers & downpours in thunderstorms.  Humid.  Winds SSE-SW at 5-15 mph, with higher gusts, along middle to upper elevation mountain ridges, shifting toward the W-WNW by evening.  Areas of fog, widespread across upper elevations.  Temps varying from the 60s to the lower 70s.


Weather Discussion ( Pattern Change )

Mesoscale Discussion – Saturday Evening

Hit-miss storms into Saturday have been productive rain producers, and this trend will continue as the conditions for more widespread activity increases into Sunday ( a total of 1.56″ of rainfall was measured in Clintwood during the 24-hour period ending at 7:00 AM Saturday ).

*As observed Saturday, a severe component has also been present with thunderstorms that form locally.  Although the potential for severe thunderstorms will diminish into Sunday, a locally strong or severe thunderstorm can not be ruled out ( especially by later in the day as drier mid-level air approaches from the west ).
NAM Model Forecast Sounding At 8 AM Sunday – Above Wise-Scott Counties

Moisture advection ( transport ) tonight into early Sunday will generate a deep, saturated vertical profile.

NAM 12 KM Model Precipitable Water Forecast At 2:00 PM Sunday – May 21, 2017

Precipitable water values approaching 2.00″ will occur into the day Sunday ( i.e., essentially the amount of water in a vertical column of air that could fall out over a single spot; however, orographics and storm circulations can work to concentrate air locally to generate much higher values ).

NAM Model 850 MB Theta-E Forecast At 2:00 PM Sunday – May 21, 2017

A strong cyclone lifting northeast into the upper Midwest will be tapping tropical moisture, as denoted by the theta-e ( potential temperature ) forecasts for Sunday.

Even as mid-level moisture begins to decrease a rich plume of low-level moisture ( high 925 MB theta-e values ) will continue to feed into the area along a frontal boundary.

*In mountainous terrain high values of low-level theta-e air are very important, since this is the air that is lifted by topographic features to help enhance precipitation production.
NAM 12 KM Model 925 MB Theta-E Forecast At 8:00 PM Sunday – May 21, 2017

Folks living along streams and in flood prone, low-lying areas will need to remain alert through Sunday for the possibility of rapid water rises.

*Only a brief break is now expected Monday before moisture values increase again into Tuesday-Wednesday to generate more rounds of significant rains.


Saturday ( Overnight ) Discussion

Thunderstorms with locally heavy rain developed during the overnight-early morning hours of Friday.

High Knob Massif Webcam – University Of Virginia’s College At Wise
Some of the heaviest rain fell across Scott County into portions of the High Knob Massif ( 0.75-1.00″ or more fell from Maple Gap into Big Cherry Lake basin, and from Natural Tunnel State Park across adjacent communities from Jasper & Duffield to Gate City ).
A humid but less “hot” Friday followed with MAX temperatures varying from 60s in upper elevations of the High Knob Massif to the middle-upper 70s ( 74 degrees in Clintwood ).

Another round of strong thunderstorms moved southeast from Kentucky across portions of southwestern Virginia into early overnight hours of Saturday.

NAM 12 KM Model Total Rainfall Forecast Next 60-Hours
While the placement of heaviest rains vary depending upon the model used, the atmospheric setting is clearly one that supports heavy to locally excessive rain.

Although many dry hours are expected through Saturday, wet ground will combine with moisture transport ahead of a slow moving upper trough and front to set the stage for thunderstorms with heavy rainfall into Sunday.


Previous Discussion

A stormy and eventually cooler trend is being highlighted as another pattern flip across the USA produces a notable change into next week.

High Knob Massif Webcam – University Of Virginia’s College At Wise

A few hit or miss showers and thunderstorms, along and northwest of the Virginia-Kentucky stateline, Thursday will give way to a renewed chance for thunderstorms overnight into Friday as a weak disturbance crosses the mountains.

Cultivated Rhododendrons Reach Peak Bloom – John & Mae Mullins Gardens

Many dry hours follow ( for places that get hit Friday ) into this weekend before shower-thunderstorm chances ramp up by later Sunday into Monday ( May 21-22 ).  This occurs ahead of large-scale ( synoptic ) changes that will push the pattern back into a cooler and wetter regime.

*A downsloping SSE-S air flow across southwestern Virginia and the eastern portions of Tennessee will tend to reduce chances of showers-thunderstorms during much of this weekend until air flow trajectories begin changing by later Sunday into Monday,  with an upward spike in precipitable water values.
Another unseasonably warm day will occur under this general downsloping pattern during Saturday, with only a chance for localized hit-miss showers-storms triggered by instability and major terrain features. 
European 51-Member Ensemble MEAN 500 MB Height Anomalies: Days 1-5

A major transition from upper ridging and anomalous warmth to upper troughing and anomalously cool air is being forecast by the ensembles.  This change is looking currently to dominate much of next week.

European 51-Member Ensemble MEAN 500 MB Height Anomalies: Days 6-10

A heavy rain-thunderstorm potential initially arises during the transition from later Sunday into Monday ( May 21-22 ).

European 51-Member Ensemble MEAN 850 MB Temp Anomalies: Days 1-5

Additional disturbances and unseasonably cool air aloft will then contribute to a wetter than average pattern under the mean upper trough, with European Model Ensemble MEAN basin average rainfall totals of 3.00″ to 5.00″ along the Appalachians through the remaining days of May.

*A similar scenario is currently being shown by the GFS Model Ensemble MEAN.  Confidence in this pattern flip is higher than average, with daily details ( with respect to clouds & chances of showers and thunderstorms ) to be worked out into next week.
European 51-Member Ensemble MEAN 850 MB Temp Anomalies: Days 6-10