034
FXUS64 KMRX 170242
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
1042 PM EDT Fri Aug 16 2024

...New UPDATE...

.UPDATE...
Issued at 1040 PM EDT Fri Aug 16 2024

Additional isolated convection is possible tonight, but widespread
or severe convection is unlikely. Mid-level lapse rates will
steepen in response to the approaching shortwave, currently near
Paducah, moving southeast. This amplified longwave troughing will
be the primary influence of our scattered diurnal convection on
Saturday afternoon.

&&

.SHORT TERM...
(This evening through Saturday)
Issued at 231 PM EDT Fri Aug 16 2024

Key Messages:

1. Numerous showers and thunderstorms this afternoon and evening
with a marginal damaging wind threat.

2. Quiet overnight but another round of scattered storms expected
again tomorrow afternoon.

Discussion:

Upper heights will continue to fall across the region as an upper
low over the Great Lakes deepens through the period and goes on to
form a synoptic scale trough across the eastern CONUS leading into
the long term period.

Locally, shortwave energy is rotating through the Tennessee valley
this afternoon and evening in the base of that developing
trough/upper low to our north. In response, showers and
thunderstorms firing along a line just coming off the Cumberland
plateau area this afternoon, should continue to increase in
coverage through the evening hours. Mesoanalysis shows somewhere
around 1,500 J/kg of mixed layer CAPE in place across much of the
CWA, along with strong low level lapse rates. Shear is lacking
though, with effective bulk shear of 25kt or less...and that is
maximized up closer to the TN/KY border. All things considered,
expect much of the convection to be your run of the mill
summertime thunderstorms. However thermodynamic profiles would
support an isolated damaging wind gust this afternoon so I
wouldn`t be surprised to see that occur. Would expect that to be
more likely in the southern plateau and southern valley areas due
to locally higher instability and downdraft CAPE values there.

Expect convection to die off fairly quickly this evening, leaving
mostly dry conditions in place. We will see increasing jet support
aloft, with the forecast area lying beneath a strengthening right
entrance region. Forecast soundings do show some meager elevated
instability as well. As such, can`t completely rule out an
isolated shower or two over our northern counties tonight. But I think
that`s the exception to the rule though.

Confidence isn`t the greatest in how Saturday plays out. We`ll be
well ahead of a front that will push through during the long term
period. So we won`t have that as a forcing mechanism. Thus
convection during the day tomorrow will be largely diurnally
driven, with any upper level forcing being subtle shortwave
activity moving through. Current PoPs reflect scattered activity
tomorrow afternoon, with a relative favoring of southern areas
where instability will be greatest. But lack of a distinct
forcing mechanism means this is somewhat of a low confidence
forecast. In terms of severe weather threats tomorrow, the threat
will be a little higher. Shear will be better, more along the
30-35kt range for effective shear versus today`s 20-25kt. So, a
slightly better environment still favoring damaging winds, but
still not a widespread severe weather type day.

&&

.LONG TERM...
(Saturday night through next Friday)
Issued at 231 PM EDT Fri Aug 16 2024

Key Messages:

1. Shower and thunderstorm chances continue through Sunday, with a
lower chance of showers in northern sections Monday.

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

Discussion:

A broad cyclonic flow will be over the eastern Conus at the start of
the period, with the center of a closed low over the Great Lakes.
Disturbances rotating around this low will keep PoPs in the high
chance to likely range for Sunday, culminating in some categorical
PoPs Sunday afternoon with the passage of an upper level trough axis
and a surface cold front. Instability and shear look too limited to
pose a severe threat. More stable conditions develop on Monday on
the back side of the trough with a NW flow pattern through the
column. However, some moisture wrapping around the closed low may
bring showers to northern sections. The categorical NBM PoPs for
Monday look way too high for this pattern and will be cut back
significantly, to chance/slight chance.

A large high pressure ridge will be developing over the Plains early
in the week, with the surface high having a slow eastward drift to
New England through the rest of the forecast period. This pattern
will favor dry conditions with below normal temperatures. Expect
highs on Tuesday in the mid 70s to mid 80s, with dewpoints dropping
into th 50s on Tuesday. A slight warming trend can be expected for
the rest of the week, but remaining near to slightly below normal.

&&

.AVIATION...
(00Z TAFS)
Issued at 715 PM EDT Fri Aug 16 2024

Showers and storms are beginning to move out of the area with
drier conditions late tonight. With clearing overnight, expect low
clouds and fog to set in at terminals, especially at TYS and TRI,
with the potential for IFR or LIFR conditions late tonight and
early Saturday morning. There is more uncertainty around CHA where
less precipitation was observed. Any fog and low clouds should
improve by 14z with another round of vcts late in the period.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             73  94  70  91 /  60  30  60  40
Knoxville McGhee Tyson Airport, TN  71  91  70  86 /  40  30  70  50
Oak Ridge, TN                       70  91  69  85 /  50  30  70  50
Tri Cities Airport, TN              68  87  66  80 /  60  20  60  70

&&

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

$$

SHORT TERM...CD
LONG TERM....DGS
AVIATION...JB