337
FXUS64 KMRX 211720
AFDMRX

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

...New AVIATION...

.UPDATE...
Issued at 1004 AM EDT Sat Sep 21 2024

A short-wave is moving across the Ohio valley producing an area of
showers and embedded storms. The greatest coverage of convection
is north of the southern Appalachians as the upper ridging is
limiting development across Kentucky and northern Tennessee.

Meso-analysis shows limited instability across much of the area
with MLCAPEs between 250-500 at best. The highest CAPE will be
across southwest Virginia and northern Plateau. Current forecast
of 20 percent PoPs across these locations look reasonable.

Otherwise, Partly sunny (north) to mostly sunny (south). An
unseasonably warm day is expected with highs in the mid 80s to
lower 90s. These values are near 10 degrees above normal.

&&

.SHORT TERM...
(Today and tonight)
Issued at 254 AM EDT Sat Sep 21 2024

Key Messages:

1. A few location may see a shower this afternoon mainly north, but
most locations will be dry for the short term period.

2. Temperatures will be above normal again.

We remain on the eastern side of the upper ridge that is centered to
our southwest. Some very weak short wave energy dropping southeast
along the periphery of the ridge may be enough to bring isolated
showers mainly to northern portions of the area this afternoon into
early evening. A rumble or two of thunder cannot be ruled out, but
convective energy looks quite limited so will just carry the
isolated showers in the forecast for now. Most areas will be dry
today and tonight, with high temperatures today again around 5 to 10
degrees above seasonal normals and low temperatures above normal as
well.

&&

.LONG TERM...
(Sunday through Friday)
Issued at 254 AM EDT Sat Sep 21 2024

Key Messages:

1. Hot weather to gradually subside into the work week.

2. A low chance exists for an isolated thunderstorm Sunday
afternoon, higher chances for unsettled weather exist Monday through
Wednesday, mainly across northern TN into VA.

3. Considerable uncertainty exists over precipitation chances late
week.

Discussion:

Expecting mostly dry conditions on Sunday as hot temperatures peak
thanks to the influence of a high pressure ridge to our south. The
GFS, HRRR, and high res FV3 all depict attempts at showers or a
thunderstorm on Sunday afternoon, especially over higher terrain of
the Plateau, so bumped up PoPs in areal coverage in response. Monday
and Tuesday a shortwave to our north helps bring light rain
primarily across our northern counties bordering Kentucky into
Virginia. Ensemble probabilities greater than a tenth of an inch QPF
during this timeframe are not great south of Knoxville.

Heading into Wednesday, a significant trough is expected to dive
down into the heart of the country and will be a major influence on
our weather through the remainder of the week. However there remains
considerable uncertainty over how the overall pattern evolves, with
major changes in guidance from even 24 hours ago. Left PoPs alone
for the latter half of the week with no clear indication of where
major weather features will evolve in that timeframe.

&&

.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             69  94  70  93 /  10  10   0  10
Knoxville McGhee Tyson Airport, TN  67  92  68  90 /  10  10  10  20
Oak Ridge, TN                       67  91  67  89 /  10  20  10  30
Tri Cities Airport, TN              62  87  63  84 /  10   0  10  50

&&

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

$$

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