Special Weather Statement, NWS Morristown, TN

AREA FORECAST DISCUSSION
National Weather Service Morristown TN
313 PM EDT Mon Jul 19 2021

.SHORT TERM (Tonight and Tuesday)...

Key Messages:

1. There is continued focus of shower/thunderstorm activity south
of I-40 through the near-term period. Locally heavy rainfall and
isolated flash flooding remain of concern.

2. Tonight's lows will be near normal in the 60s to near 70 with
seasonally milder highs tomorrow in the upper 70s to mid 80s.

This Evening/Tonight

Currently, a mid/upper low is located near the intersection of the
Mississippi and Ohio River Valleys with a 60+ kt downstream jet
streak. Additionally, a developing surface low is noted south of
the upper low along with a cold frontal boundary located south of
I-40. With continued upper divergence via ageostrophic
circulations and low-level convergence via the surface low,
southern portions of the area remain the focus for more persistent
showers and thunderstorms. It is also noted that PWAT values are
near 2" in these areas, meaning that efficient rainfall rates are
expected within any stronger storms this evening and through the
overnight period. This is also coupled with mean 3850-300mb wind
vectors of 10 kts or less. As such, locally heavy rainfall and
isolated flooding will remain of concern and will continue to be
mentioned in the HWO through tonight. In southwest Virginia and
northeast Tennessee, the convective environment is more conducive
to locally strong wind gusts if any notable convection does
develop via better mid-level dry air and better lapse rates.
Otherwise, any convection outside of southern portions of the area
is expected to be spotty and decrease with diurnal instability
loss overnight.

Tuesday

Heading into tomorrow, the upper low will move northward, pulling
the largely weak surface disturbance towards the area. This
progression, along with diurnal instability, will allow for showers
and thunderstorms to continue throughout the day, mainly well south
of I-40. There remains potential for locally heavy rainfall and
isolated flooding from training convection, but is likely to
limited overall due to limited heating from cloud cover. With most
model guidance keeping the coverage fairly limited, low
probability HWO wording will be kept for the day tomorrow with
largely milder temperatures for this time of year.

BW

.LONG TERM (Thursday Night through Monday)...

Key Messages:

1. Diurnal showers and thunderstorms possible during the middle of
the work week, but coverage should be more limited.

2. Better chances for rain over the weekend into next week with an
approaching front.

Discussion:

By Tuesday night the front will be along or just south of the
Tennessee Valley and the strong ridge over the western/central parts
of the country remains locked in place. On the east coast a weak
trough will slowly try to push southward, but it's main influence
will remain closer to New England. Models continue to hint at a
small shortwave/low moving eastward out of Memphis on Tuesday and
the remnants of that system could still be impacting us by Tuesday
night into early Wednesday morning meaning showers and thunderstorms
on Tuesday evening could last a bit longer into the overnight hours
than we've previously seen with these diurnal storms.

During the middle and second half of the work week the moisture from
the Gulf looks like it may start to get suppressed and remain
further to the south leading to lower coverage and chances for
afternoon storms. Think that we will see showers and thunderstorms
most afternoons, but expect coverage to be more limited. Still a bit
up in the air with regards to how far north the moisture is able to
go Wednesday through the end of the work week... But went a bit
drier than guidance as it seems to be over estimating storm coverage
in the current weather regime we've been under the influence of
lately.

Better chances for showers and thunderstorms will come at the end of
the weekend and into next week as a system rides around the northern
edge of the mega-ridge out west and should try to dive southeastward
towards the Tennessee Valley. Have slightly increased precipitation
chances at the end of the long term forecast, but didn't go too wild
because again, still think that weather models have been
overestimating precipitation chances recently.

ABM

&&

.AVIATION...
18Z TAF DISCUSSION.

Notable aviation impacts are expected at the TAF sites with
continued MVFR/IFR at CHA, largely driven by scattered to numerous
showers and thunderstorms. It is likely that TRI and TYS will
remain mostly VFR this afternoon, outside of potential impact
from a shower or thunderstorm into the early evening. CHA is
expected to remain MVFR with IFR reductions remaining possible.
Overnight, all sites are expected to drop to MVFR or lower with
the worst conditions at TRI and CHA. Potential exists for LIFR
from fog or localized low ceilings. Otherwise, conditions should
improve at TYS and TRI by mid-morning with MVFR likely lingering
at CHA due to continued rain showers and lower ceilings.

BW

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             70  78  68  86  70 /  70  60  40  40  10
Knoxville McGhee Tyson Airport, TN  69  79  67  88  69 /  40  50  20  30  10
Oak Ridge, TN                       69  80  66  87  67 /  30  40  20  20  10
Tri Cities Airport, TN              65  82  63  88  65 /  30  30  10  20   0

&&

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

Hazardous Weather Outlook
National Weather Service Morristown TN
306 PM EDT Mon Jul 19 2021

NCZ060-061-TNZ012>018-035>047-067>074-081>087-098>102-VAZ001-002-
005-006-008-201915-
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-
306 PM EDT Mon Jul 19 2021 /206 PM CDT Mon Jul 19 2021/

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

.DAY ONE...This Afternoon and Tonight

Scattered to numerous showers and thunderstorms will continue
this afternoon and into tonight, especially south of the I-40
corridor. Locally heavy rainfall is possible, which may lead to
localized flooding.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not needed at this time.

Special Weather Statement
National Weather Service Morristown TN
452 PM EDT Mon Jul 19 2021

TNZ069-070-073-192130-
Jefferson TN-Knox TN-North Sevier TN-
452 PM EDT Mon Jul 19 2021

...SIGNIFICANT WEATHER ADVISORY FOR EAST CENTRAL KNOX...WESTERN
JEFFERSON AND NORTHWESTERN SEVIER COUNTIES UNTIL 530 PM EDT...

At 451 PM EDT, Doppler radar was tracking a strong thunderstorm 7
miles northwest of Sevierville, moving northwest at 10 mph.

Pea size hail and winds in excess of 30 mph will be possible with
this storm.

Locations impacted include...
Knoxville, Sevierville, New Market, Strawberry Plains, McMahan,
Mascot, Piedmont, Kodak and House Mountain State Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Heavy rainfall is also occurring with this storm, and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent lightning is occurring with this storm. Lightning can
strike 10 miles away from a thunderstorm. Seek a safe shelter inside
a building or vehicle.

&&

LAT...LON 3587 8369 3606 8386 3613 8371 3608 8366
      3612 8368 3612 8365 3610 8365 3610 8363
      3612 8363 3613 8364 3614 8364 3614 8362
      3613 8361 3616 8360 3615 8359 3617 8358
      3595 8349
TIME...MOT...LOC 2051Z 153DEG 8KT 3598 8364

TD