913
FXUS64 KMRX 211916
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
316 PM EDT Sat Sep 21 2024

...New SHORT TERM, LONG TERM...

.SHORT TERM...
(This evening through Sunday)
Issued at 240 PM EDT Sat Sep 21 2024

Key Messages:

1. Isolated showers and possibly a thunderstorm through early
evening. Greatest coverage over the Plateau and southwest
Virginia/northeast Tennessee.

2. Unseasonably hot conditions today and again Sunday.
Temperatures near 10 degrees above normal.

Discussion:

A weak wave is rotating around the upper ridge across the Ohio
valley and central Appalachians. Meso-analysis shows best
instability across the northern Plateau into southwest
VA/northeast Tennessee with MLCAPES of 500-1000. These areas have
the best chance of showers and possibly a thunderstorm through
early this evening.

Locations that see any rainfall will have a decent chance of fog
development overnight. Otherwise, partly cloudy sky with a stray
shower possible.

For Sunday, upper ridge remains over the region allowing for
another unseasonably hot day with temperatures from 5 to 10
degrees above normal. HREF and deterministic models agree with
another short-wave moving toward the area during the afternoon.
MLCAPES will be best across the Plateau and western sections of
the Tennessee valley. Widely scattered to scattered late day
showers and possibly a thunderstorm are expected.

&&

.LONG TERM...
(Sunday night through next Saturday)
Issued at 240 PM EDT Sat Sep 21 2024

Key Messages:

1. Increasing chance of convection during the extended but
confidence is low on probabilities and timing due to evolution of
the tropical system in the gulf.

2. Can not stress enough to not focus on deterministic models on
timing, strength, and location of tropical systems late this week.
Main message is that the CPC is depicting a greater than 60
percent probability of tropical development in the Gulf.

Discussion:

For Monday through Wednesday, ensemble cluster analysis shows a
slow change in the upper level pattern with a northern and
southern stream short-waves weakening the upper ridge over the
area. This will allow for increasing coverage of convection over
the region especially along and north of interstate 40. Some much
needed rainfall is possible.

For Thursday through Saturday, forecast confidence decreases as
CPC probabilities shows tropical development in the gulf combined
with continued upper trough over the mid-section of the nation.
The evolution of these systems will play a large role in the
timing, direction, and strength of the tropical system and
associated rainfall.

&&

.AVIATION...
(18Z TAFS)
Issued at 116 PM EDT Sat Sep 21 2024

Main concerns during the forecast period will be the potential of
fog development across TRI between 08-12Z Sunday. Due to lack of
fog development last night and overall dry soil conditions, will
keep conditions no lower than MVFR.

Otherwise, VFR conditions are expected with weak pressure gradient
producing light winds, less than 10 knots.

Isolated showers will develop across the Plateau counties and
southwest Virginia and northeast Tennessee but confidence is not
high to include in the TAFs.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             70  94  70  93 /   0  10   0  20
Knoxville McGhee Tyson Airport, TN  68  92  68  90 /  10  10  20  30
Oak Ridge, TN                       68  91  67  89 /   0  20  20  40
Tri Cities Airport, TN              62  88  63  84 /   0  10  20  60

&&

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

$$

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