-- Discussion containing changed information from previous version are highlighted. --
990
FXUS64 KMRX 092311
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
711 PM EDT Wed Jul 9 2025

...New AVIATION...

.SHORT TERM...
(This evening through Thursday)
Issued at 1244 PM EDT Wed Jul 9 2025

Key Messages:

1. Scattered thunderstorms this evening - strong thunderstorms and
heavy rain rates.

2. Diurnal thunderstorms expected again on Thursday, but lower
coverage and primarily far eastern counties of the forecast area
near the NC state line.

Discussion:

Upper-level shortwave trough will continue to rotate eastward
today with southwest flow aloft ahead of this feature. A warm,
unstable airmass will be present across the area with RAP forecast
MLCAPE around 2000 J/Kg expected, primarily east of Interstate
75. Forecast soundings indicate a saturated profile and high
freezing level above 15k ft; resulting in a deep warm cloud layer
depth. With PW values between 2.0 and 2.2 inches across the area,
heavy rain rates are expected this evening - and localized flash
flooding will be the primary risk with some of these rainfall
rates around 3"+ per hour. Frequent lightning and isolated strong
downburst winds will be possible with the stronger thunderstorms,
as well.

The most likely regions for seeing rainfall today will be across
the northern two-thirds of the forecast area where synoptic
forcing is more favorable to convective initiation. Looking at NBM
probabilities for greater than 0.25 inches of rainfall this
evening, TRI has around a 70% to 80% chance, TYS is around 50% to
60%, and CHA is around 30% to 40%. With the heavy rain rates, if
any thunderstorms remain over, or multiple storms track over, one
specific location for an hour or two, localized flash flooding
will be likely for these spots. This evening will be our highest
probability of rainfall that we`ve had so far this week, and will
likely be our highest chance of rain through the rest of the
week and into the weekend, as well.

Shortwave axis shifts eastward by Thursday morning with primary
support for convective initiation on Thursday afternoon near the
far eastern Tennessee mountain zones and into North Carolina.
Chances of rain and thunderstorms will decrease with distance west
of the mountains.

&&

.LONG TERM...
-- Changed Discussion --
(Thursday night through next Wednesday)
Issued at 1244 PM EDT Wed Jul 9 2025

Key Messages:

1. Drier weather expected Friday behind the shortwave.

2. Upper-level ridge brings hot weather this weekend into early
next week. Diurnal convective trends continue into next week.

3. Weak shortwave may bring more widespread scattered convection
on Monday afternoon and evening.

Discussion:

Upper-level ridge begins to build in from the west on Friday with
northwest flow and subsidence aloft. It should be mostly clear and
mostly dry with perhaps a few isolated showers or thunderstorms.
As the 591-594 dam upper-level ridge builds in this weekend across
the Mid-South, hot weather is expected with temperatures in the
low 90s and heat index values approaching 100F. Diurnal,
summertime convection is expected with the highest probabilities
for thunderstorms near the higher elevations.

A quick moving shortwave will shift east across the Ohio Valley
and Great Lakes on Monday with the center of a 594 dam upper-level
ridge retrograding across the Lower Mississippi Valley. This will
place us between these two features, and with the shortwave
passing nearby, will likely give us a slightly higher chance of
more widespread scattered convection on Monday afternoon and
evening.

The ridge will continue to retrograde slowly westward placing us
in a hot, humid environment with northwest flow aloft. There are
hints of some subtle shortwaves/MCVs rotating around the ridge
towards the middle of next week. While hot, mostly dry weather
will be the prevailing forecast, MCS activity will bear watching
across the region based on this pattern.
-- End Changed Discussion --

&&

.AVIATION...
-- Changed Discussion --
(00Z TAFS)
Issued at 707 PM EDT Wed Jul 9 2025

Showers and storms will continue over the next couple of hours
with activity having passed just east of TRI and CHA. TYS could
see reductions from a storm in the next hour or two, so a TEMPO
was maintained. Activity will diminish through the evening with
development of vicinity fog around TYS and TRI with TRI
potentially seeing off and on reductions by early morning. During
the day on Thursday, winds will generally be from the west or
southwest with clouds around 5,000 feet AGL. Showers and storms
will develop by the afternoon again with the best coverage
currently to be around CHA.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             72  88  71  91 /  50  70  20  50
Knoxville McGhee Tyson Airport, TN  71  87  70  91 /  70  70  20  40
Oak Ridge, TN                       70  86  69  90 /  60  70  10  40
Tri Cities Airport, TN              68  84  67  87 /  80  80  30  50

&&

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

$$

SHORT TERM...JB
LONG TERM....JB
AVIATION...BW