-- Discussion containing changed information from previous version are highlighted. --
575
FXUS64 KMRX 171446
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
1046 AM EDT Fri May 17 2024

...New UPDATE...

.UPDATE...
-- Changed Discussion --
Issued at 1023 AM EDT Fri May 17 2024

Main focus with the update was tweaking PoP grids to align with
the most recent radar trends. Did try to limit categorical
wording as some models suggest slightly less coverage than
previous runs. GOES-16 water vapor imagery depicts relatively
drier air across portions of western Tennessee, western
Mississippi, and Arkansas. Given potential for pockets of this dry
air to make way through mean flow, can agree with some of these
recent 12Z model trends. Overall, the forecast messaging is in
good shape as periods of rain and perhaps occasional thunder will
be possible this afternoon.
-- End Changed Discussion --

&&

.SHORT TERM...
(Today and tonight)
Issued at 259 AM EDT Fri May 17 2024

Key Messages:

1. Showers will overspread the area today and continue into tonight,
and there may be a few thunderstorms as well.

Discussion:

We start the period under SW flow aloft with upper level short wave
energy approaching from our southwest, and a surface frontal
boundary well to our south. The better jet forcing looks to stay to
our south today, and the stronger convection is expected to stay to
our south as well and will likely help to inhibit much significant
instability from making it into our area.  Right now, most model
sources suggest limited instability over our area, with the HREF
showing mean MUCAPES staying below 500 J/kg, and probabilities of
reaching 500 J/kg of SBCAPE generally well below 50%.  Showers will
spread across the area generally from SW to NE today and continue
into tonight, and some rumbles of thunder will be possible as well.
The main threat with any storms will be localized heavy rainfall,
and localized flooding will be possible mainly if training of cells
were to occur.  With the clouds and precipitation today, high

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 259 AM EDT Fri May 17 2024

Key Messages:

1. Scattered afternoon thunderstorms on Saturday, Sunday to be less
wet.

2. Drier and warmer Monday and Tuesday as ridging builds.

3. Cold front to bring additional showers into the area mid to late
week.

Discussion:

Weak upper trough gradually will move through the wider region this
weekend, helping to fire more showers and thunderstorms. Saturday
morning looks to be on a drying trend, with any lingering convection
to dissipate. Looking at CAM soundings, enough instability is in
place Saturday afternoon to fire showers and thunderstorms. Severe
wise not likely to see any organized convection, with weak 0-6 km
shear, but 1200 to 1500 J of CAPE should help fuel thunderstorms. As
with any convection, lightning will be the big risk for Saturday
outdoor activities along with gusty winds and small hail during the
storms` brief individual lifespans.

A few lingering showers or storms are possible on Sunday, but the
bulk of the rainy period will be moving on with the trough to the
Carolinas. Meanwhile upper level ridging will begin to build in to
fill the void, allowing for warmer temperatures and drier weather
the first half of the workweek next week. Wednesday afternoon
temperatures have increased since yesterday`s afternoon forecast,
with the next trough and cold front combo appearing slower in the
latest guidance. If that holds, Chattanooga could flirt with 90F at
midweek. At some point on the back half of the week the front will
slide through, and along with associated rain showers Thursday will
be cooler than Wednesday. Not too enthused on severe chances,
especially with the parent low (regardless of model timing) ejecting
quickly to the Great Lakes with questions on front orientation and
strength as it approaches East Tennessee, but we can work out those
details as we get closer.

&&

.AVIATION...
(12Z TAFS)
Issued at 618 AM EDT Fri May 17 2024

Some brief fog to start at TRI. Otherwise, showers and perhaps
some rumbles of thunder will spread across the area from SW to NE
today and will continue into tonight. Given lower probability and
large timing uncertainty will leave thunder out of the forecasts
for now. Will likely see conditions lower to MVFR/IFR at CHA and
TYS, with conditions likely lowering to MVFR at TRI by the end of
the period.

&&

.PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN             72  64  81  64 /  80  30  70  40
Knoxville McGhee Tyson Airport, TN  73  63  77  62 /  60  50  80  60
Oak Ridge, TN                       72  63  77  62 /  60  60  60  50
Tri Cities Airport, TN              73  60  75  60 /  70  50  60  60
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&&

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

$$

SHORT TERM...
LONG TERM....Wellington
AVIATION...