Johnson City, Tennessee 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

242
FXUS64 KMRX 121813
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
213 PM EDT Tue Aug 12 2025

...New DISCUSSION...

.DISCUSSION...
Issued at 141 PM EDT Tue Aug 12 2025

Key Messages:

1. Heavy rainfall, high rainfall rates, and localized flash
flooding are possible from this afternoon through Wednesday.

2. Scattered to widespread showers and embedded storms.

3. Reduced converage of storms for the latter half of the week
through early next week. Return to hot and muggy conditions as
well with heat indices increasing to mid 90s to near 100 degrees
across much of the Tennessee and Sequatchie valleys.

Discussion:

...Localized Excessive Rainfall and Flash Flooding Possible from
this Afternoon through Wednesday...

A tropical wave across the northern Gulf and southwest flow into
the Tennessee valley and southern Appalachians will pull abundant
tropical moisture into the region. Ensemble and deterministic
models show PWs increasing to 2.1 to possibly 2.3 inches which is
2-3 standard deviations above normal or 99th percentile. There is
also weak 850mb moisture transport. A series of weak vorts/shear
axis will move north into the periphery of the ridge into the
Appalachians enhancing convection. Also, local terrain will also
focus potential of enhanced rainfall.

The REFS and HREF are in agreement with the potential of locally
heavy rainfall and flash flooding. Ensemble mean has a more
defined 3"+ in localized areas. On the fence for issuing a flash
flood watch. Would feel much more confident to issue a watch is a
boundary was evident across the region focusing the convection.

Held off issuing a watch given collaboration with the surrounding
WFOs but will send out DSS briefing and SPS highlighting the
threat.

Besides the potential of heavy rains, plenty of tropical moisture
will keep sky mostly cloudy and keep temperatures below normal
through mid-week.

For Thursday, upper trough will move into the area and weaken.
Scattered showers and thunderstorms will be expected with the main
concern being localized flash flooding.

For Friday into early next week, ensemble cluster analysis shows
increasing heights with upper ridge building into the mid-section
of the nation. End result will be decreasing chances of mainly
afternoon and early evening storms. Most of the convection will be
confined to the higher terrain, especially far east Tennessee
mountains and southwest North Carolina which is farther away from
upper ridge axis.

Also temperatures will increase with highs in the lower and middle
90s and heat indices of 95 to 100 over much of the Tennessee and
Sequatchie valleys.

&&

.AVIATION...
(18Z TAFS)
Issued at 110 PM EDT Tue Aug 12 2025

Will have showers and thunderstorms around through the period, and
timing at any given site is not possible to pin down. Will carry a
lot of VCSH and VCTS with a tempo and prob30 group at each site
trying to time the higher probability periods. Expect VFR and
MVFR conditions for the most part all sites, but lower conditions
can be expected in heavier precipitation.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             73  86  72  89 /  70  70  40  50
Knoxville McGhee Tyson Airport, TN  72  86  72  88 /  60  70  50  40
Oak Ridge, TN                       72  85  71  88 /  70  70  50  40
Tri Cities Airport, TN              69  83  69  84 /  80  70  60  60

&&

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

$$

DISCUSSION...DH
AVIATION...