Severe Thunderstorm Warning 124, NWS Morristown, TN

AREA FORECAST DISCUSSION
National Weather Service Morristown TN
317 PM EDT Fri Jul 24 2020

.SHORT TERM (Tonight and Saturday)...
Convection will decrease in coverage after loss of daytime heating
and the associated stabilizing of the atmosphere. Expect clearing
conditions overnight with fog near areas that received rainfall.

Upper ridging remains anchored across the middle of the nation
with a 594-595dam upper 500mb ridge centered across Kansas and
Missouri producing weak northerly flow across the region. Low
level SE flow between a ridge across the Mid- Atlantic and
Tropical Storm Hanna near south Texas. This will continue to
produce an area of weak 850mb-700mb convergence across southern
and central portions of the forecast area. Synoptic forcing is
very weak on Saturday allowing mesoscale factors to be the primary
contributors to convective development and organization. With
daytime heating, instability will be on the increase with NAM
soundings showing MLCAPE between 1500 to 2500 J/Kg by early
afternoon. With differential heating along the higher terrain,
thunderstorm initiation is expected by midday. Pulse convection
will be the primary mode with deep layer shear less than 10 kt. In
addition, DCAPE values will be higher on Saturday which may
enhance the risk of isolated microbursts with descending
thunderstorm cores. HREF guidance shows low-level moisture will
remain high with PW values across the southern half of the
forecast area between 1.8 to 2.0 inches contributing to locally
heavy rainfall and isolated flooding. Convective coverage will
follow a diurnal curve with a decrease in activity during the late
evening and early overnight hours.

JB

.LONG TERM (Saturday night through Friday night)...
Through the weekend, an elongated ridge of high pressure aloft
will stretch from the southern plains east through the mid
Atlantic. A northern stream shortwave will move through southern
Canada and the northern plains. Typical summertime weather will
result with afternoon scattered showers and thunderstorms
expected. Temperatures near to slightly above normal can be
expected Saturday night and Sunday. On Monday, the northern stream
shortwave drops out of southern Canada and into the Great Lakes
with an attendant cold front moving through the Ohio valley. Lower
heights and southerly low level flow will enhance precipitation
chances Monday and Monday night before the cold front approaches
on Tuesday. Increased cloud cover and precipitation should keep
temperatures slightly cooler on Monday.

Frontal passage occurs on Tuesday and Tuesday night. Upper
disturbance ejects northeast allowing the cold front to weaken as it
moves through the region. Coverage of showers and thunderstorms
should pick up on Tuesday with this period likely having the highest
PoPs. Start to see model diverge regarding the strength of the ridge
across the southeast. The ECMWF seems to break the ridge down more
with a more amplified pattern while the GFS keeps the ridge,
although still weak. However, guidance does agree that northwest
flow will setup across the Tennessee valley toward the end of the
period with continued chances of showers and thunderstorms and near
normal temperatures.

Diegan

&&

.AVIATION...
18Z TAF DISCUSSION.

Scattered showers and thunderstorms are expected this afternoon
with the highest coverage forecast to be near TYS and CHA. This
will result in tempo MVFR, and potential brief IFR, conditions.
Convection will decrease after sunset with drier conditions
overnight. With some clearing, expect patchy fog to develop.
Highest confidence in MVFR or lower vis is at TRI where guidance
is in good agreement with MVFR or IFR fog development late
tonight and early Saturday morning.

JB

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             73  92  72  91  73 /  30  40  20  50  20
Knoxville McGhee Tyson Airport, TN  71  90  71  91  72 /  20  30  20  50  20
Oak Ridge, TN                       71  90  70  91  71 /  20  40  20  50  20
Tri Cities Airport, TN              67  89  67  89  68 /  30  30  20  50  20

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&

Hazardous Weather Outlook
National Weather Service Morristown TN
319 PM EDT Fri Jul 24 2020

NCZ060-061-TNZ012>018-035>047-067>074-081>087-098>102-VAZ001-002-
005-006-008-251930-
Cherokee-Clay-Scott-Campbell-Claiborne-Hancock-Hawkins-Sullivan-
Johnson-Morgan-Anderson-Union-Grainger-Hamblen-Northwest Cocke-
Cocke Smoky Mountains-Northwest Greene-Southeast Greene-
Washington-Unicoi-Northwest Carter-Southeast Carter-Roane-Loudon-
Knox-Jefferson-Northwest Blount-Blount Smoky Mountains-
North Sevier-Sevier Smoky Mountains-Sequatchie-Bledsoe-Rhea-Meigs-
McMinn-Northwest Monroe-Southeast Monroe-Marion-Hamilton-Bradley-
West Polk-East Polk-Lee-Wise-Russell-
319 PM EDT Fri Jul 24 2020 /219 PM CDT Fri Jul 24 2020/

This Hazardous Weather Outlook is for portions of southwest North
Carolina...east Tennessee and southwest Virginia.

.DAY ONE...This Afternoon and Tonight

Scattered showers and thunderstorms are expected this afternoon
and early evening with a few strong to marginally severe storms
possible. Isolated damaging wind gusts and brief heavy rainfall
are the main concerns.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter reports of severe weather or flooding are encouraged.
Please relay any information about severe weather to the NWS while
following local, state, and CDC guidelines.

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Special Weather Statement
National Weather Service Morristown TN
331 PM EDT Fri Jul 24 2020

TNZ015-038-242015-
Hancock TN-Grainger TN-
331 PM EDT Fri Jul 24 2020

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN HANCOCK AND
NORTHEASTERN GRAINGER COUNTIES UNTIL 415 PM EDT...

At 331 PM EDT, Doppler radar was tracking a strong thunderstorm near
Bean Station, or 12 miles southwest of Sneedville, moving northeast
at 5 mph.

Winds in excess of 40 mph will be possible with this storm.

Locations impacted include...
Treadway.

LAT...LON 3641 8322 3640 8328 3639 8328 3635 8339
      3641 8343 3642 8342 3641 8342 3642 8341
      3641 8339 3643 8337 3645 8337 3650 8328
TIME...MOT...LOC 1931Z 238DEG 6KT 3640 8336

Diegan

Special Weather Statement
National Weather Service Morristown TN
344 PM EDT Fri Jul 24 2020

TNZ013-036-242030-
Anderson TN-Campbell TN-
344 PM EDT Fri Jul 24 2020

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN ANDERSON AND
SOUTHERN CAMPBELL COUNTIES UNTIL 430 PM EDT...

At 344 PM EDT, Doppler radar was tracking a strong thunderstorm 8
miles west of Jacksboro, or 12 miles west of La Follette, moving
southeast at 15 mph.

Winds in excess of 40 mph will be possible with this storm.

Locations impacted include...
Clinton, Jacksboro, Caryville, Rocky Top, Norris, Norris Dam State
Park, Disney, Cove Lake State Park and Andersonville.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3628 8400 3627 8401 3621 8397 3608 8408
      3608 8409 3606 8409 3604 8411 3624 8437
      3625 8437 3628 8436 3628 8433 3631 8433
      3636 8430
TIME...MOT...LOC 1944Z 302DEG 14KT 3630 8434

Diegan