471
FXUS64 KMRX 231720
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
120 PM EDT Sun Jun 23 2024

...New AVIATION...

.UPDATE...
Issued at 1117 AM EDT Sun Jun 23 2024

No significant changes were made to the forecast for this
afternoon. A trough is moving into the region from the Ohio
Valley this afternoon. The surface cold front is currently (1120
AM EDT) near SE Missouri/NE Arkansas. Hi-res guidance suggests
that the line of rain with some embedded thunder moving into
Middle Tennessee will dissipate as it moves into our region late
this afternoon and early evening. The best chance for strong
showers and storms will probably be mid to late evening as the
cold front moves into Middle Tennessee. The threat for severe
storms looks marginal with CAPE less than 1000 and the front
approaching the region after sunset. A few strong to severe storms
cannot be ruled out mainly in the Plateau Counties. Showers and
storms will likely be scattered and some locations may not even
get any rain.

&&

.SHORT TERM...
(Today and tonight)
Issued at 309 AM EDT Sun Jun 23 2024

Key Messages:

1. Thunderstorms arrive from the northwest this evening. A few could
pose a damaging wind risk over the northern plateau region, but most
will be run of the mill storms.

2. Hot weather continues today, with highs in the low to mid 90s in
the southern valley, before we get a bit of a reprieve in the long
term period.

Discussion:

A shortwave trough and associated surface low will shift east
through the Great Lakes region today into tonight, with a cold front
extending southwest through the Ohio valley this afternoon and
evening. Ahead of the front, scattered showers and thunderstorms are
expected to develop, with additional convection expected along the
front. In the updated Day 1 Outlook, SPC has maintained a marginal
risk area clipping our northern plateau counties, mainly for a
limited risk of damaging winds. There`s some discrepancy on the
arrival time, but most guidance points to the arrival of storms
being around 00z or shortly thereafter. HREF ensemble mean fields
point to there still being around 1,000 J/kg of surface based CAPE
in that area as storms move in, which will be coincident with some
20-30kt effective deep layer shear and 0-3km SRH values upwards of
100 m2/s2. All of this would support some cluster type convection
capable of a stray damaging wind gust. Will continue to mention in
the HWO, but that being said it`s not exactly a significant severe
weather threat. Further south and east, the arrival time of storms
doesn`t support much in the way of a severe threat. Expect just
general thunderstorms.

Otherwise, expect another hot day today with highs reaching into the
low to mid 90s, warmest in the south. Lowered dewpoints a fair
amount from the NBM, choosing to side with the CONSShort guidance
which was performing better over the last few hours with respect to
observations. This yields some afternoon RH values in the 35-40
percent range for the southern valley. Even with the lower
dewpoints/resulting RH, heat index values will still be in the upper
90s in the south.

&&

.LONG TERM...
(Monday through Saturday)
Issued at 309 AM EDT Sun Jun 23 2024

Key Messages:

1. Continued above normal temperatures, but a couple of days not
quite so hot.

2. Although we will have chances of showers and storms, most areas
will still get below normal precip for the week.

In the early parts of this forecast period we are under an upper
level northwest flow, while a couple of shortwaves push through the
area in this flow, then by Friday, the old upper ridge comes surging
back over us again, that continues into the weekend.

Meanwhile at the surface, on Monday weak high pressure will be
covering the area in the wake of a weak cold front. By Wednesday we
have a return flow out of the south ahead of the next shortwave on
Wednesday, and then a cold front and reinforcing shortwave move
through around Wednesday night or early Thursday. Surface high
pressure should be in control by Friday, with the next return flow
starting up again on Saturday.

During this heatwave, temperatures are their own topic.  Monday and
Tuesday will not be as hot as the last several days, then Wednesday,
with the return flow, will likely be hot and humid again. But then
another cold front passes, and the reinforcing shortwave may keep
clouds around longer, so Thursday may be the most comfortable day of
the week.  With the upper ridge moving back in for Friday and
Saturday the heat will likely be "on" again.

Also, during this heatwave it has been dry.  The precip totals for
the Wednesday/Thursday showers and storms looks to mainly be between
only 0.10" and 0.30" for us, so most areas will not get any "game
changer" precipitation.

For the intensity of storms Wednesday or Wednesday night, the
setting looks a little less organized than it did in yesterday`s
model runs, with a couple of weak shortwaves racing through the
flow, rather than one strong shortwave. We will keep an eye on it
as it gets closer.

&&

.AVIATION...
(18Z TAFS)
Issued at 112 PM EDT Sun Jun 23 2024

VFR conditions are expected outside of thunderstorms. Scattered
showers and isolated storms are expected this evening. Thunder
potential is low to medium since storms will likely be isolated as
a cold front approaches after sunset. Winds will become more
northerly but light tomorrow morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             74  95  69  94 /  40  10   0  10
Knoxville McGhee Tyson Airport, TN  72  91  65  92 /  50  10   0  10
Oak Ridge, TN                       71  90  65  92 /  50  10   0  10
Tri Cities Airport, TN              69  86  60  88 /  60  10   0   0

&&

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

$$

SHORT TERM...CD
LONG TERM....GM
AVIATION...McD