680
FXUS64 KMRX 230517
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
117 AM EDT Mon Sep 23 2024

...New AVIATION...

.UPDATE...
Issued at 1000 PM EDT Sun Sep 22 2024

Another quick update to add some isolated showers and
thunderstorms into the southeast Tennessee are for the next
couple hours as some light showers with some lightning is moving
southeast into the southern plateau counties.

&&

.SHORT TERM...
(This evening through Monday)
Issued at 303 PM EDT Sun Sep 22 2024

Key Messages:

1. Isolated showers and storms continue overnight. Fog expected
for any area that receives rain.

2. Isolated to scattered showers and storms tomorrow.

3. Hot again tomorrow, temps around 5 to 10 deg above normal.

Discussion:

A few isolated showers and storms will continue through the night
as weak short wave energy passes through the region. Any area
that receives rainfall will likely see fog thereafter.

Tomorrow, the flow becomes more zonal as high pressure shifts to our
southeast. This zonal flow, combined with additional shortwave
energy moving through, will increase chances of showers and storms
across the area. Though there will be increased coverage, not all
areas will see showers or storms. There is a marginal risk for
severe storms tomorrow but I am not that excited about it. The
reason for the marginal is increased shear in the mid to upper
levels with 0-6km shear around 30kts. Shear in the lower levels is
weak to non-existent. With the increased mid to upper shear, storms
will be able to be longer lived than summer-time pulse variety.
However, mid level lapse rates of 4 to 5 C/km are unimpressive. The
main threat with any stronger storm will be gusty winds due to some
drier air at the surface. Again though, not that excited about the
severe potential.

&&

.LONG TERM...
(Monday night through next Sunday)
Issued at 303 PM EDT Sun Sep 22 2024

Key Messages:

1. A significant pattern change is in the offing during the extended
period with ridging aloft being replaced by a trough over the mid-
section of the nation. End result, increasing chances of much needed
rainfall across the region.

2. Ensemble Prediction System along with the latest deterministic
models are beginning to align with a significant tropical cyclone
developing in the Caribbean and Gulf of Mexico then moving north.

3. Depending on how this tropical cyclone interacts with the upper
trough over the mid-section of the nation and upper ridge over
Florida, this low may move into the Tennessee valley and southern
Appalachians late week.

Discussion:

For Monday night and Tuesday, first in series of short-waves lift
out of the developing mid-nation upper trough. Best dynamics will be
over the northern half of the region. MLCAPES will be in the 750-
1500 range with very limited mid-level lapse rates and shear. Main
concern will be lightning and gusty winds up to 30-40 mph Tuesday
afternoon.

For Tuesday night and Wednesday, the upper trough continues to
deepen over the mid-section of the nation with a frontal boundary
becoming quasi-stationary over the Tennessee valley. MLCAPES of 500-
100 with PWS around 1 standard deviation above normal per NAEFS.
Main concern will be locally heavy rainfall. Storm motion will be
nearly parallel with the boundary so can not rule out localized
runoff issues.

For Thursday into next weekend, a significant tropical system will
likely (40-60 percent probabilities of development in the Caribbean
and Gulf of Mexico) be affecting the Gulf coast states. Latest
Ensemble Forecast System (EPS) and deterministic models showing this
low moving north into the Tennessee valley and southern
Appalachians. Here are the potential concerns:

1. Heavy rainfall and flash flooding, especially the Plateau,
southeast Tennessee, and southwest North Carolina.
2. Windy conditions, especially for the favored mountain wave high
wind areas of far east Tennessee Mountains, and the Plateau.

As this system eventually develops, models will likely form more of
a consensus of track and timing, and potential impacts.

&&

.AVIATION...
(06Z TAFS)
Issued at 1256 AM EDT Mon Sep 23 2024

There remains some potential for fog early in the period, but it
does not look probable enough to include for now. There will be
some showers and thunderstorms around during the period, and will
try to time the most likely period with a prob30 thunderstorm
group all sites. Outside of any showers/storms, will go with a VFR
forecast for the period all sites. Winds will generally be light,
although may become gusty with any storms.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             92  69  91  69 /  30  20  40  50
Knoxville McGhee Tyson Airport, TN  90  67  89  67 /  50  30  60  70
Oak Ridge, TN                       89  66  86  66 /  50  20  70  70
Tri Cities Airport, TN              85  64  83  64 /  60  30  70  70

&&

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

$$

SHORT TERM...TD
LONG TERM....DH
AVIATION...