Severe Thunderstorm Warning 142, NWS Morristown, TN

AREA FORECAST DISCUSSION
National Weather Service Morristown TN
251 PM EDT Fri Jul 31 2020

.SHORT TERM... (Today through Tomorrow)...
A line of showers and thunderstorms across Middle Tennessee will
continue move eastward south of the front through the rest of the
afternoon and evening. Satellite imagery shows that the eastern
Tennessee Valley has cleared today allowing temperatures to warm and
the atmosphere to destabilize after the round of morning storms.
Mesoanalysis indicates upwards of 2500 J/kg of MLCAPE over east
Tennessee this afternoon. DCAPE values this afternoon are around 800
J/kg, but very little shear this far north. In addition the PWAT
values will remain very high, close to 2 inches, meaning there will
be abundant moisture for storms to tap into. So the main threats
with storms this afternoon remains strong straight-line winds and
heavy downpours leading to flooding. High resolution CAMs are
indicating this initial wave moves through this afternoon helping to
stabilize and clear out most of the area, but another round moving
out of middle Tennessee up towards the Cumberland Plateau closer to
midnight as the surface low and front move nearer to the region.

With all the rain we've already received and more expected this
evening, we may see fog develop overnight and into the morning
hours, especially along the Cumberland Plateau over towards SW
Virginia where rain will occur later in the evening/night.

Tomorrow, the front will be approaching the region, and another
round of showers and thunderstorms can be expected ahead of it.
Better jet dynamics closer to the low/trough means that storms will
be capable of becoming more organized in the afternoon/evening, but
shear still looks somewhat weak at this point based on forecast
soundings. A lot of it will depend on how much we clear out
tonight/tomorrow ahead of any storm formation. But once again, the
biggest threat with storms tomorrow will be damaging straight-line
winds and heavy downpours leading to flooding.

ABM

.LONG TERM...(Saturday night through Friday)...
Overall, not much change compared to the last long term issuance.
We begin the period with an unseasonably deep trough across the
area. This trough lingers through Tuesday night/Wednesday and will
allow for increased chances for showers and storms.

Saturday night, a surface low is lifting off to the northeast into
the Ohio River Valley. A few lingering storms can be expected from
the afternoon hours but coverage should be on the decrease. The cold
front associated with the low passes through Saturday night but will
get hung up across the Appalachians on Sunday. This will provide
focus for showers and storms through the day but with the highest
POPs along the foothills of the Appalachians and Appalachians
themselves. Chance POPs in place elsewhere. On Monday, another area
of low pressure moves down into the existing trough and into the
Ohio River Valley. The associated cold front will begin to move
across west TN through the day. At the same time, what is currently
Hurricane Isaias, will be approaching the coastal Carolinas and
spreading moisture northwest into the Appalachian region. The
approaching cold front and increasing moisture from Isaias will
provide another day of chance and likely POPs. Tuesday we step back
down to Chance POPs across all areas as drier air moves in behind
the front. Temperatures during this period will be in the low to mid
80s, which is near normal to a few degrees below normal.

Wednesday through Friday the flow begins to become more zonal as the
trough lifts off to the north. During the time, we can expect a
return to normal summer-time conditions where the highest POPs will
be along the high terrain with lower chances down in the valley.
This activity will be diurnally driven, which is what we expect for
this time of year. Temperatures during the last few days of the
period will be warming back into the mid and upper 80s, closer to
normal.

SR

&&

.AVIATION...
18Z TAF DISCUSSION.

Line of storms currently across Middle Tennessee is expected to
move eastward through the afternoon. Conditions should likely
remain VFR but if/when a storm hits it will quickly degrade with
strong storms. Should recover relatively quickly after storms move
through. Depending on where rain occurs this afternoon/evening we
could see fog develop tomorrow morning, but left it out of the
TAFs due to uncertainty at this time. Another round of storms is
expected tomorrow.

ABM

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             73  90  70  88  68 /  50  50  30  30  30
Knoxville McGhee Tyson Airport, TN  72  91  71  87  68 /  60  50  40  40  30
Oak Ridge, TN                       71  89  69  87  67 /  60  50  40  30  30
Tri Cities Airport, TN              69  90  69  86  66 /  60  50  40  60  50

&&

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

Hazardous Weather Outlook
National Weather Service Morristown TN
241 PM EDT Fri Jul 31 2020

NCZ060-061-TNZ012>018-035>047-067>074-081>087-098>102-VAZ001-002-
005-006-008-011845-
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-
241 PM EDT Fri Jul 31 2020 /141 PM CDT Fri Jul 31 2020/

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

.DAY ONE...This Afternoon and Tonight

A round of storms is expected this afternoon through this
evening. A moist and unstable airmass will produce scattered
strong to possible severe thunderstorms. Main concern will be
torrential rains and potentially more flash flooding. Isolated
damaging winds are also possible.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Strong to severe storms will be possible late Saturday afternoon
into the evening. Best chances for severe weather will generally
be along and west of Interstate 75. The main threat from these
storms will be isolated damaging wind gusts. Heavy rainfall with
these storms could also lead to the possibility of localized flash
flooding.

A strong to marginally severe storm cannot be ruled out again on
Sunday afternoon across northeast Tennessee and southwest
Virginia with an isolated damaging wind gust being the main
threat.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon and again on
Saturday.

Special Weather Statement
National Weather Service Morristown TN
420 PM EDT Fri Jul 31 2020

TNZ067-083-084-312045-
Rhea TN-Roane TN-Meigs TN-
420 PM EDT Fri Jul 31 2020

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN RHEA...NORTHEASTERN
MEIGS AND SOUTHWESTERN ROANE COUNTIES UNTIL 445 PM EDT...

At 419 PM EDT, Doppler radar was tracking a strong thunderstorm near
Spring City, or 13 miles southwest of Rockwood, moving northeast at
15 mph.

Pea size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Rockwood, Spring City, Grandview, Piney Falls State Park and Eagle
Furnace.

LAT...LON 3575 8493 3578 8490 3578 8488 3583 8480
      3582 8478 3586 8473 3590 8471 3590 8468
      3570 8454 3565 8486
TIME...MOT...LOC 2019Z 240DEG 12KT 3574 8485

CED