671
FXUS64 KMRX 041105
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
705 AM EDT Thu Jul 4 2024

...New AVIATION...

.SHORT TERM...
(Today and tonight)
Issued at 358 AM EDT Thu Jul 4 2024

Key Messages:

1. Hot weather to continue today. Heat indices will range from the
mid 90s in Virginia to the low 100s in the southern TN valley. See
Heat Advisory for more information.

2. Chance of showers and thunderstorms today. Storms across northern
Tennessee into southwest Virginia this afternoon may contain strong
gusty winds up to low end severe criteria in the strongest cell of
the day.

Discussion:

Upper ridge strength has technically weakened for today, with a weak
shortwave ahead of the larger trough and cold front helping to
flatten the ridge. However, model 850mb temperatures are warmer, and
with continued weak southwesterly flow expecting today to be
slightly warmer, slightly muggier across the Tennessee valley. In
accordance with that, have opted for a Heat Advisory to match the
worst locations, principally south of Interstate 40. With
temperatures remaining elevated into the night (Chattanooga has been
in the mid 80s at midnight last two nights), a reminder to remain
hydrated while celebrating the nation`s birthday even after sunset.

The Storm Prediction Center has a marginal risk for severe wind
draped across the northern edges of Tennessee and southwest
Virginia. The struggle today will be to once again convect in the
face of warm air aloft. High-res guidance isn`t exactly enthused
about the scenario, so overall PoPs are just chance in the north.
Still, should a storm manage to intensify an updraft, can imagine it
becoming strong enough for 40 to 60 mph downdraft winds in the hot
and humid atmosphere. Thunderstorms should diminish or outright
dissipate tonight after sunset, so nature`s fireworks are not
expected to interfere with celebrations. The one thing to keep in
mind tonight is a standard low level inversion will set up
overnight, so don`t be surprised if firework smoke remains trapped
close to the surface.

&&

.LONG TERM...
(Friday through Wednesday)
Issued at 358 AM EDT Thu Jul 4 2024

Key Messages:

1. Hot Friday, with increased chances for showers and storms Friday
and Friday night with a frontal passage

2. Drier weather returns during the weekend, then PoPs increase
again.

3. Temperatures will continue to run a little above normal for much
of the period.

Discussion:

We start the period with a low pressure system approaching the
western Great Lakes region, with a cold front trailing into the mid
Mississippi Valley region and the Southern Plains. The low pressure
system will move east through the Great Lakes Friday and Friday
night, pulling the cold front through our area Friday night/early
Saturday. The atmosphere will be rather moist ahead of the front,
with models showing PWAT values generally exceeding 2 inches Friday.
HREF ensemble data indicates much of the area has a 40-70 percent
chance of exceeding 2000 J/kg of SBCAPE, and MLCAPES look likely to
be in the 1000-1500 J/kg range.  Model soundings indicate DCAPES
will likely exceed 700 J/kg as well.  This suggests a potential for
a few strong to marginally severe thunderstorms Friday with damaging
winds the primary threat, although weak deep layer shear will be a
limiting factor in this potential.  Much of this activity will
likely be focused along a pre-frontal trough that moves through
Friday afternoon/early Friday evening time frame, with the cold
frontal passage occurring later Friday night/early Saturday.

The other concern for Friday will be the heat especially south, as
dewpoints look likely to be high enough that with temperatures
expected to top out in the lower 90s in most valley locations, there
is potential for heat index values to approach or even briefly climb
above 105 mainly across portions of the southern Valley.  However,
there are still significant uncertainties on timing of precipitation
and the details of how much cloud cover will be around which may act
to hold things down a bit, so no heat advisory will be issued for
Friday at this time.

Some convection may linger into Saturday especially eastern portions
of the area depending on the speed of the front, but drier air will
be filtering in behind the front Saturday. Sunday will be mainly dry
as well, although there may be some isolated weak convection in the
eastern mountains.

By early in the week high pressure will be off to our east, and a
broad upper trough will be set up over the Plains. This upper trough
will gradually shift east during the remainder of the period.
Moisture will begin to increase again, and chances for showers and
thunderstorms will increase as well for the Monday through Wednesday
time frame.

Temperatures will generally run a bit above normal for the long term
period, although they may tick down slightly Wednesday.

&&

.AVIATION...
(12Z TAFS)
Issued at 700 AM EDT Thu Jul 4 2024

VFR should be predominant through the TAF period at all sites.
There is a slight chance for scattered SHRA during the afternoon
and early evening, though thunder is low probability. PROB30 still
in at TRI where coverage may be enough to lend confidence to
terminal impact. Winds will remain light. Dependent on rainfall,
fog bringing at least MVFR visibility is most likely at TRI late
in the period.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             96  78  93  75 /  20  20  70  50
Knoxville McGhee Tyson Airport, TN  95  77  91  74 /  20  20  70  70
Oak Ridge, TN                       94  76  91  72 /  30  30  70  60
Tri Cities Airport, TN              91  71  91  71 /  40  20  70  70

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...Heat Advisory from 2 PM EDT /1 PM CDT/ this afternoon to 8 PM
     EDT /7 PM CDT/ this evening for Bradley-Hamilton-Loudon-
     Marion-McMinn-Meigs-Northwest Blount-Northwest Monroe-Rhea-
     Roane-Sequatchie-West Polk.

VA...NONE.
&&

$$

SHORT TERM...Wellington
AVIATION...Wellington