Johnson City, Tennessee 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

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FXUS64 KMRX 052350 AAA
AFDMRX

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
750 PM EDT Fri Sep 5 2025

...New UPDATE, AVIATION...

.UPDATE...
Issued at 736 PM EDT Fri Sep 5 2025

Main focus for the evening update was to tweak PoPs for the
remainder of the evening and overnight hours. While an isolated
shower/thunderstorm or two have skirted parts of our plateau this
afternoon, our CWA has been precip free. The forecast was a bit
too aggressive in bringing rain chances in from the west, so I
toned them back to align with recent HRRR runs which seem to be
handling things pretty well to our west across middle TN. Not a
huge change, but it does narrow down our window of chances of
rain/severe weather tonight a bit better.

Speaking of which, the day shift`s thoughts on severe chances are
very still accurate I think. Perhaps the only change would be to
suggest there`s a possibility of some slightly larger hail than
previously thought. But that is a minor change as the threat of
large hail was always secondary to damaging winds. And that, by
far, remains the primary hazard. Timing wise, it looks like storms
will move into our plateau areas around 10pm EDT and across the
I-75/I-81 corridors towards midnight or so. The timing isn`t great
for severe storms but numerous pieces of guidance, including SPC`s
HREF, show odds are favorable that surface-based CAPE will still
be available as they arrive so I don`t think we can confidently
say the threat of damaging winds will diminish after sunset.

The latest high res guidance (HRRR and other CAMs) suggest this
will be east of us by daybreak tomorrow morning.


&&

.DISCUSSION...
Issued at 120 PM EDT Fri Sep 5 2025

Key Messages:

1. Another round of thunderstorms expected this evening with the
primary hazards being strong winds and hail.

2. Keep an eye on radar this evening and have an indoors location to
be able to wait out the storms if/when they do move through.

3. After rain moves out of the area this weekend, expect dry weather
next week with a general warming trend.

Discussion:

We`re in a lull in storm activity, which should continue through
much of the afternoon hours. A front that is currently near the main
stem of the Mississippi River will continue to work its way eastward
today. Ahead and along this line the atmosphere will destabilize
enough that another round of thunderstorms is expected this evening
with severe thunderstorms possible.

With pressure`s rising ahead of the front and clearer skies the
atmosphere will heat up today with temperatures expected to climb
into the 80`s across much of the eastern Tennessee Valley, almost 10
degrees warmer than what we experienced yesterday. This heating will
help to destabilize the atmosphere in preparation for the expected
line of showers and thunderstorms later in the evening. Forecast
soundings and CAM`s are coming into agreement that the atmosphere
will be supportive of possibly seeing damaging winds in the
strongest storms tonight with very dry air in the 700-300mb range
giving us the chance to see downbursts from these storms, producing
gusts up to around 70mph. There will also be enough CAPE present in
the hail growth zone that we could see another round of hail with
this event... However with storms expected to be more linear in
nature and hail likely to have less residence time in the
thunderstorms it`s looking like it will be hard to see hail like we
experienced yesterday, with hail 1" or smaller looking to be much
more likely. Cannot completely rule out an isolated tornado this
evening, but the better environment and more discrete cells are
expected over middle TN and central KY, but if a supercell did form
it could possible maintain it`s strength into the eastern half third
of Tennessee.

Lowest confidence part of tonight forecast is the timing of this
system with CAMs displaying a wide variety of solutions for when the
primary round of storms moves through. More aggressive models have
convection developing ahead of the front along the Cumberland
Plateau around 22z with many more holding off convection along the
plateau until 00-02z. Unfortunately regardless of which ends up
happening the storms will likely impact Friday evening outdoor
activities such as high school football in some counties.

Key weather message for today is to keep an eye on the radar to see
if storms are headed your way and have an indoors shelter to be able
to duck into while these storms pass overhead.

Overnight we could see additional (much weaker) showers and storms
as the main portion of the trough moves through. These weaker
showers and storms could linger through Saturday before finally
moving out in the back half of Saturday. We`ll see a noticeable
cooldown on Saturday with temperatures likely to stay in the 70`s
for much of the eastern Tennessee Valley. Weak troughing that
eventually turns into more zonal flow that then in turn morphs into
a broad ridge over the US will lead to quiet and calm weather for
next week. A slow warming trend is expected with highs back into the
mid to upper 80`s by the end of the work week.

&&

.AVIATION...
(00Z TAFS)
Issued at 736 PM EDT Fri Sep 5 2025

Incoming thunderstorms should affect all terminals later this
evening/tonight. Flight categories will drop significantly as they
move through but should rebound afterwards at KTYS and KCHA.
Guidance supports some brief, but notable, decreases in VSBY and
CIGS at KTRI behind the convection early tomorrow morning. This
seems reasonable as any clearing conditions would allow for quick
fog/low cloud development. Another round of SHRA/TSRA is expected
for all sites tomorrow, but it should be around or after 18z and
timing wasn`t certain enough to include just yet. Will address in
the 06z TAF package.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             69  81  61  80 /  50  60  10   0
Knoxville McGhee Tyson Airport, TN  68  77  59  77 /  50  70  20   0
Oak Ridge, TN                       67  76  57  77 /  60  70  10   0
Tri Cities Airport, TN              64  77  58  74 /  50  70  30   0

&&

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

$$

DISCUSSION...CD
AVIATION...CD