071
FXUS64 KMRX 171439 AAA
AFDMRX

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
1039 AM EDT Sat Aug 17 2024

...New UPDATE...

.UPDATE...
Issued at 1030 AM EDT Sat Aug 17 2024

Confidence is low regarding the timing and location of convective
development today. Satellite shows a lot of low cloud cover,
suggesting plentiful low level moisture, but the 12Z OHX sounding
hasa dry layer around 700 mb that suggests dry air entrainment
will be a limiting factor that will need to be overcome for
development. There is also some low level stability in the OHX
sounding and NAM forecast soundings. A more favorable factor will
be an entrance region of a jet streak that will be moving across E
KY and WV this afternoon, providing some upper divergence. The
general expectation is that convection will be developing in the
early and mid afternoon hours in the Plateau, with scattered to
isolated coverge as it moves east into the TN Valley. Gusty winds
are possible with storms but the threat of damaging wind is low.

A better chance of showers/storms comes tonight with a more well-
defined midlevel shortwave trough and jet streak providing better
synoptic forcing. This overnight round may also have a better
potential for severe storms; this will be more closely analyzed
once the 12Z models come in.

&&

.SHORT TERM...
(Today and tonight)
Issued at 302 AM EDT Sat Aug 17 2024

Key Messages:

1. Scattered showers and thunderstorms are expected this afternoon
and evening. Some storms may be severe with the primary threat
damaging winds.

2. Showers and storms will continue tonight but coverage will be
more isolated.

Discussion:

A trough is deepening over the Ohio Valley today into tonight.
Multiple rounds of showers and thunderstorms will be possible
today and tonight but coverage looks highest late afternoon and
evening as a shortwave moves through the region. The upper low and
surface low will be vertically stacked over the Great Lakes today.
The cold front will move through Sunday morning. Isolated showers
and thunderstorms will continue this morning. This afternoon
activity will become more scattered although still somewhat hit
and miss. CAMs and the NBM are favoring the late afternoon and
evening timeframe for best coverage.

CAPE will be highest in the afternoon around 1000 to 2000 J/Kg.
Shear will be highest in the evening around 40 knots. By the time
the shear increases, instability will be much lower. Still, severe
parameters look good enough for a marginal damaging wind threat in
the afternoon and evening. After midnight tonight, CAMs agree
that coverage will be more isolated.

With a later start to thunderstorms expected in most locations
this afternoon, minimal cloud cover will allow highs to reach 90
in much of the Tennessee Valley.

&&

.LONG TERM...
(Sunday through Friday)
Issued at 302 AM EDT Sat Aug 17 2024

Key Messages:

1. Shower and thunderstorm chances continue through Monday, mostly
confined to northeast TN/southwest VA, but storms are expected to be
weaker.

2. Dry weather and near to below normal temperatures expected for
much of next week.

Discussion:

Sunday night into Monday will be the final chances for precipitation
for the next several days as we continue to sit towards the base of
the slow moving trough/low over the eastern United States. Best
chance to see storms will be north of Interstate 40, and especially
near the TN/VA border, however there will be much less moisture in
the atmosphere for storms to tap into and overall QPF amounts should
be fairly light for those places that do see a quick round of rain
heading into Monday. For the majority of people the main weather
story for the end of the weekend and into next week will be the
cooler temperatures and lower dew points.

Sunday will likely be the last day of widespread 90+ degree
temperatures for several days as we sit on the eastern edge of a
strengthening ridge over the central United States, which will lead
to generally drier air out of the north/northwest across the eastern
Tennessee Valley. Not only will this help keep temperatures several
degrees below seasonal normals, it will also keep the dew point
values much lower than we`ve seen over the weekend. So the main
story for the upcoming week ahead (once we get past Mondays storm
potential) will be a unusually pleasant and cool back half of
August. Next best chance for precipitation might not come until
after the weekend, but large model variances does not lead to high
confidence at this time.

&&

.AVIATION...
(12Z TAFS)
Issued at 719 AM EDT Sat Aug 17 2024

Isolated to scattered showers and thunderstorms will continue
throughout this forecast period. This activity will be hit and
miss and timing is very uncertain but multiple rounds of storms are
possible. Patchy fog and low CIGs will clear by mid morning. Fog
and low CIGs are possible again tomorrow morning near TRI.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             91  72  90  68 /  40  20  30   0
Knoxville McGhee Tyson Airport, TN  90  70  86  66 /  20  40  60  20
Oak Ridge, TN                       88  69  84  66 /  30  40  60  10
Tri Cities Airport, TN              86  66  79  64 /  30  60  80  40

&&

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

$$

SHORT TERM...DGS
AVIATION...McD