686
FXUS64 KMRX 181340 AAB
AFDMRX

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
940 AM EDT Thu Jul 18 2024

...New UPDATE...

.UPDATE...
Issued at 929 AM EDT Thu Jul 18 2024

A cold front was situated from the northern plateau counties, to
just east of Crossville, and finally southwest towards the middle
TN and Alabama state line region as of 9 am. Rain chances in the
forecast reflected much higher chances for rain south and east of
the front than what current radar trends were indicating, so I
made some significant adjustments to the PoPs through late morning.
Blended in a heavy dose of the 11z HRRR as well as the NAMNest to
adjust PoPs to something a little closer to current reality. That
said, I think the afternoon forecast still looks reasonable so no
changes there. Otherwise, also made some adjustments to the
dewpoints through the afternoon hours as well. Blended in a heavy
dose of NAMNest there too, which tamped down the high-end dewpoint
values in the southern TN valley. Will update the FWF to account
for this as well.

&&

.SHORT TERM...
(Today and tonight)
Issued at 313 AM EDT Thu Jul 18 2024

Key Messages:

1. Light to moderate showers with a low chance of a rumble of
thunder or two this morning. Best chances generally north if I-40.
Additional scattered showers and storms this afternoon.

2. Temperatures will trend seasonally cool this afternoon.

Discussion:

SPC mesoanalysis suggest we remain under the periphery of the right
entrance region of a jet atop the southern Great Lakes & Ohio
Valley. Associated upper level divergence is aiding in sustaining
weak convection across portions of KY and TN. With the loss of
daytime heating and the atmosphere gradually stabilizing, lightning
has been rather sparse with decreasing precip efficiency over the
last hour. Main impacts through the morning hours will be light rain
with some patchy steam fog, but dense fog is not generally expected
due to poor radiational cooling conditions.

A weak surface boundary currently located from Memphis northeastward
into Ohio will progress through the forecast area late morning into
mid-day. This frontal forcing and increased troughing influence will
promote additional convective initiation this afternoon, though this
may be more focused to areas south and east of Interstates 40 & 81
depending on the exact timing of the frontal passage. The veering of
winds to the north will usher in cooler and drier air. RAP soundings
suggest MLCAPE will be close to 1000J/kg with DCAPE generally less
than 800 J/kg, thus, the chance for any stronger storms seems less
favorable this afternoon. SPC has clipped our northeastern areas in
a marginal risk likely do to enhanced effective shear(20-25kts)
closer to jet influence. With the downward trend in energy relative
to this past afternoon, have opted to utilize low probability
wording in the HWO. Precip chances come to an end for the overnight
with continued trends of seasonally cool temperatures.

&&

.LONG TERM...
(Friday through Wednesday)
Issued at 313 AM EDT Thu Jul 18 2024

Key Messages:

1. A welcome and unsettled pattern will persist through the long
term with daily chances for showers and storms.

2. Slightly below normal temperatures are expected through the
extended.

Discussion:

A cold front will be to our south to begin the period. Then,
moisture begins to spread north back into our area on Friday as a
shortwave moves northeast through Mississippi. Our best chances for
precip will come during the afternoon hours, as peak heating and
increasing moisture coincide. However, the best chances for precip
will be across our southern areas, closer to the cold front. With
lesser chances across Northeast TN and southwest VA. The cold front
will then transition to a warm frontal boundary and will lift north
into our area on Saturday. With increased forcing from the
shortwave, frontal boundary, and additional moisture, Saturday will
be another good opportunity for widespread showers and storms. The
warm front will be slow to move north and will remain situated along
the TN/KY line for Sunday. This will once again provide another
great opportunity to receive additional much needed rainfall.

POPs remain elevated Monday through Thursday as moisture continues
to stream in from the Gulf. This is due to the Bermuda high across
the Atlantic and general troughiness to our west. Both GFS and ECMWF
ens guidance continues to show PWAT values in the 75th to 90th
percentile through this timeframe, which is large contributor to the
elevated POPs.

&&

.AVIATION...
(12Z TAFS)
Issued at 709 AM EDT Thu Jul 18 2024

Expect MVFR cigs present at TRI to hang on through the morning,
but should lift as additional scattered showers and storms develop
along and behind a front this afternoon. Low confidence in direct
impacts due to expected coverage so TAFs simply mention vicinity
thunder for the time being. Light winds will also veer more
northerly following the fropa. Guidance hits TRI pretty hard with
fog tonight but low confidence at this point.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             88  70  85  70 /  60  20  60  60
Knoxville McGhee Tyson Airport, TN  84  68  85  70 /  60  20  60  70
Oak Ridge, TN                       84  66  85  68 /  50  10  50  60
Tri Cities Airport, TN              80  63  85  67 /  50  10  40  60

&&

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

$$

SHORT TERM...CD
AVIATION...KRS