Mountain Area Forecast ( June 22-23 )

ALERT For Severe Thunderstorm Development During Wednesday-Thursday.  A Major Wind Damage Event Is Likely Within Or Close To The Cumberland Mountains And Mountain Empire

Wind Damage, Large Hail, Vivid Lightning & Flooding Rainfall Will Be The Main Severe Threats.  This Could Result In Power Outages For Impacted Locations.

Updated at 6:00 PM Thursday – Individual supercell thunderstorms across Kentucky are forming into a squall line that will be the main feature of concern Thursday Evening-Night for counties across the Cumberland Mountains and Mountain Empire

A stormy weather pattern, anchored by a major heat dome to the west, is taking shape with strong-severe storms becoming likely during the Wednesday-Thursday period as part of a major severe weather outbreak.

Mesoscale Convective Systems ( large thunderstorm clusters ) are expected to develop, with potential for Derecho or near-Derecho Formation ( a long-lived wind damage producing system ).

More localized strong-severe thunderstorm development will also exist as dewpoints and instability increase through Wednesday. Please stay tuned to NOAA Weather Radio for possible watches and/or warnings that will be likely.

Tuesday Night Into Wednesday Morning

A chance of showers & thunderstorms.  SW-W winds 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges.  Temperatures widespread in the 60s.

Wednesday Afternoon Into Wednesday Night

Showers & thunderstorms likely.  Some storms could be strong to severe with wind damage and flooding rainfall.  SSW-W winds 10-20 mph, with higher gusts.  Temperatures varying from upper 60s-lower 70s across highest elevations to the upper 70s to lower 80s.  Very humid.

Thursday Morning Into Thursday Night

Showers & thunderstorms likely.  Some storms could be strong to severe with wind damage and flooding rainfall.  SW-W winds 10-20 mph, with higher gusts.  Temperatures varying from 60s to low 70s in the morning to the 70s to lower 80s into the afternoon.  Very humid.

Although details remain to be worked out, I have significant concern that a flash flood setting could also emerge across portions of the mountain area.

*NOTE that high-resolution models change radically due to the nature of convection over short-time periods.  Therefore, it is most important to FORECAST THE PATTERN in a setting like this and not depend upon any given model run.

 

Weather Discussion ( June 21-23 )

Early Thursday Afternoon Update

A Tornado Watch is now in effect for Dickenson and Buchanan counties until 10:00 PM Thursday ( June 23 ).

Remember that a WATCH means conditions are favorable for tornadoes IN AND CLOSE TO the watch area.

The atmosphere today is so unstable that there has been explosive thunderstorm development during the mid-afternoon, with radar indicating cloud tops soaring to more than 60,000 feet into the steamy atmosphere.

The Storm Prediction Center indicated that a watch would be coming during the early afternoon, which is no surprise given increasing instability ( high CAPE-moisture values to go along with SHEAR ) in presence of outflow boundaries generated by the overnight Thunderstorm Complex that passed just north and northeast of the Cumberlands.

More than 30,000 homes & businesses lost electricity across West Virginia on the AEP Network overnight into Thursday morning.

Meanwhile, a flash flood emergency has been declared in portions of the eastern mountains, from Richwood in Nicholas County into the Greenbrier County area.  Outside of that area at least 1 person has reportedly been swept away by flooding in West Virginia.  In fact, WSAZ-TV reports at least 30 flood rescues in progress across the state at 5:45 PM Thursday.

The updated risk region has the northern end of the Cumberland Mountains touching the Enhanced Risk.

 

Early Thursday Overnight Update

Counties along the Virginia-Kentucky border once again took the burnt of strong-severe thunderstorms Wednesday, with prolific lightning, heavy rain, and local wind damage.

Wednesday ( June 22 ) MAXS remained in the 70s in Norton-Wise and Clintwood ( 75 degree MAX ) as debris cloudiness coming in from thunderstorms toward the northwest, and subsequent storm development, held air temperatures down versus locations south toward the Tri-Cities ( where 85 to 90 degrees was common ).

A major thunderstorm cluster that is near the Maddox definition for a true Mesoscale Convective Complex or MCC formed Wednesday evening across the Upper Midwest.

Note the dramatic increase in size as denoted by colorized Infrared Satellite Imagery showing the expansion of cold cloud tops which are associated with deep convection ( thunderstorms ).

These are the most prolific lightning producing systems on planet Earth, so a tremendous “light show” is ongoing.  “Heat” lightning will be seen far to the south as the complex drops farther S-SE.

For some reason, perhaps some contamination of sounding data, short-range models like the HRRR resolved the storms better up until the 00z ( evening ) data was ingested.

Recent HRRR future Doppler forecast’s have lost the storm line over Illinois into Indiana.  So it becomes more “interesting” with respect to how far south and southwest the MCS-MCC develops versus a more eastward trend currently forecast by the HRRR.

Climatology shows that such systems typically build farther south and southwest ( toward the inflow side ) and turn more right of the general flow field over time ( as I noted previously, the MesoHigh or cold pool forces system relative low-level convergence to help dictate the propagation over time ).  The important area that HRRR recent runs have missed, over Illinois into Indiana, being the point outward from which there is beautiful upper divergence as seen on above Infrared images.

Numerous tornado and many wind damage reports have been documented from Illinois and Indiana into Ohio.

My thinking remains essentially unchanged, as despite what happens into Thursday morning it is very likely that new development forms during the afternoon-evening to renew the severe threat ( with wind damage and flooding rainfall remaining the primary threats outside of always dangerous lightning and localized hail ).

An outflow boundary from this MCS-MCC ( near Derecho ) system will act as a notable focus for new development Thursday, amid a very unstable air mass with high CAPE and instability.  This will likely, unless the area is very lucky, lead to a more widespread severe event Thursday versus that experienced Wednesday.

Continue to stay tuned to NOAA Weather Radio and your favorite media sources for more watches and/or warnings which will be likely once again Thursday.

 

Previous Discussion

Reference my 062116 Forecast Discussion for more details.

Strong to severe thunderstorms impacted portions of the mountain region during Tuesday as instability & moisture increased along and ahead of a surface frontal boundary.

Factors conducive to a major severe weather outbreak are now becoming better defined, with a serious threat of one or more clusters of severe thunderstorms.

Potential for a Derecho is increasing, with a major wind damage event coming close ( to the north ) or hitting the Cumberland Mountains by Thursday.

Meanwhile, a lead thunderstorm cluster currently from Iowa into Illinois could drop southeast and trigger strong to severe thunderstorm development Wednesday in advance of the next major storm complex.

One reason I have become very aggressive with this forecast is that even IF the main Derecho complex misses hitting the area directly, a major outflow boundary is likely to act as a focus for new severe thunderstorm development Thursday toward the inflow side ( warm-very unstable ) of the system across eastern Kentucky and southwestern Virginia.

Such a setting also increases the potential for flash flooding to develop, since a tendency for back-building convection is climatologically favored amid a more westerly 850 MB flow field ( beneath WNW flow aloft ) along any boundaries that are present to act as a low-level focusing mechanism ( in combination with terrain features ).

*Some homes were flooded in Harlan County during Tuesday amid an air mass that possessed a lower total water content than that expected Wednesday into Thursday.

The Bottom Line…A serious severe weather outbreak is likely to develop Wednesday into Thursday, impacting locations within or very close to the Mountain Empire.

Please stay tuned to NOAA Weather Radio and your favorite media sources for updates and likely watches and warnings that will be needed.