-- Discussion containing changed information from previous version are highlighted. --
771
FXUS64 KMRX 301755 AAC
AFDMRX

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
155 PM EDT Tue Apr 30 2024

...New AVIATION...

.UPDATE...
Issued at 1021 AM EDT Tue Apr 30 2024

The precip shield associated with the upper trough moving through
has begun to fall apart, which was expected. However, expect there
to be a resurgence of shower activity this afternoon with further
daytime heating and the passage of a part of the trough that is
essentially a quasi-upper low. A combination of HRRR and NBM
hourly PoPs were used to update rain chances through the afternoon
hours. It looked very reasonable and models in the additional
shower activity that`s expected. The other noteworthy change as
far as rain goes, is that I removed thunder from the forecast
through 18z. There have been no lightning strikes detected within
our CWA all morning and that likely doesn`t change until this
afternoon. Lastly, I didn`t touch anything in regards to high
temperatures. The forecast looked OK there and was in line with
most guidance.

&&

.SHORT TERM...
(Today and tonight)
Issued at 244 AM EDT Tue Apr 30 2024

Key Messages:

1. Showers with a few thunderstorms move through today.

2. Showers end this evening followed by low clouds and fog
developing overnight.

Discussion:

Precip approaching the area from the west appears to be driven
mainly by QG forcing ahead of a shortwave trough and a jet
entrance region, enhanced by a nocturnal LLJ of 30-35 kt. These
dynamics will maintain the precip into the western half of the
area in the next few hours, but the lack of instability will be a
limiting factor as it moves east of I-75. Very few lightning
strikes have been observed in Middle TN and northern AL, and IR
satellite shows cloud top temperatures have remained steady state.
The forecast for this morning will have categorical PoPs west of
I-75 with just a slight chance of thunderstorms. All CAMS show a
weakening and dissipating trend to the precip after 12Z as it
moves east of Knoxville where there is very little to no CAPE.
However, there may be some additional development this afternoon
as the shortwave trough brings some cooler temperatures aloft.
Some CAMS show development in the northern Plateau around 18-20Z
that spreads east, and stays mainly north of I-40. The forecast
will have a chance of showers and thunderstorms continuing into
the evening to account for this possibility. This chance should
end after sunset once the trough moves east of the area and dry
air aloft builds in.

Tonight, a surface high will quickly build over the area, with a
moist boundary layer remaining in place. This appears to be a
good setup for some fog or low clouds to form later in the night,
and several models are picking up on this. Areas of fog will be
mentioned for the entire area late tonight.

&&

.LONG TERM...
(Wednesday through Monday)
Issued at 244 AM EDT Tue Apr 30 2024

Key Messages:

1. Continued above normal temperatures at least through next week,
with the highest temperatures well above normal occurring Thursday.

2. Active weather pattern to bring chances for showers and
thunderstorms Friday and continuing through early next week.

Discussion:

At the start of the extended period Wednesday, skies will be
clearing after a cold frontal passage earlier Tuesday. Wednesday
will begin a considerable warm-up in temperatures from today.
Surface high pressure and ridging aloft will bring the 80 plus
temperatures back to the region. Thursday still should be the
warmest day of the next several with mid to upper 80s for highs in
valley. Skies will start out clear Thursday night but an increase in
clouds will move in late at night as another weak system with a cold
front crosses the western Great Lakes early Friday and increases
moisture over the Tennessee Valley during the day Friday.

A secondary low is expected to form Friday morning over the mid
south and lower Mississippi Valley Friday. It is expected to merge
with the northern system and then move east into the eastern
Tennessee Valley by sunset. A deep upper trough will be to the north
of the Tennessee Valley and keep the slow moving system moving
through Saturday and then keep the front just to the south Sunday. A
good chance of showers and some thunderstorms through Saturday night
or early Sunday. Long range models show a possible break in the rain
Sunday into early Monday as the ECMWF shows the upper flow becomes
more zonal Sunday into Sunday night but the GFS is more active with
good chances for more activity Sunday and Monday as shortwaves move
through along and near the slow moving frontal system. Kept good
rain chances the last 2 days due to the uncertainty. Temperatures
after Thursday will stay in the upper 70s to lower 80s.

&&

.AVIATION...
-- Changed Discussion --
(18Z TAFS)
Issued at 134 PM EDT Tue Apr 30 2024

Radar shows some ISOLD to SCT SHRA developing north of I-40
through the Cumberland plateau. High res guidance gives mixed
reviews on how far south additional development will occur, and
tend to believe that it won`t be much. Given trajectories, will
limit any SHRA mention to just KTYS through this afternoon. Later
this evening and overnight, high pressure will settle in and
cloud cover will scatter out as a result. Expect prime conditions
for radiational fog and low clouds to develop. Currently have KTYS
and KTRI going down to 1/2SM FG, but left KCHA at 3SM. Confident
they`ll get fog, just not as confident in how low flight
categories drop there.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             75  58  84  59 /  90  10   0   0
Knoxville McGhee Tyson Airport, TN  71  56  81  57 /  90  10   0   0
Oak Ridge, TN                       72  55  82  57 /  90  10   0   0
Tri Cities Airport, TN              70  55  78  53 /  80  40   0   0

&&

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

$$

SHORT TERM...CD
LONG TERM....TD
AVIATION...CD