428
FXUS64 KMRX 162323
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
723 PM EDT Tue Jul 16 2024

...New AVIATION...

.SHORT TERM...
(This evening through Wednesday night)
Issued at 229 PM EDT Tue Jul 16 2024

Key Messages:

1. Isolated to scattered showers and thunderstorms this evening,
tonight, and Wednesday.

2. Increasing humidity will result in heat index values near or
over 100F.

Discussion:

To say that the short term forecast is uncertain would be an
understatement. There are many complicating factors to consider.
First, an upper-level jet will strengthen overnight with a jet
streak of over 100 kt. A strong shortwave will amplify troughing
across the Upper Mississippi Valley and Great Lakes, too. This
will enhance ascent across the Great Lakes and Ohio Valley with
increasing SW/WSW 850 mb winds in response.

At the surface, there is a defined outflow boundary near the
Interstate 40 corridor from early morning convection across
western KY. Ongoing convection along the deformation axis and
higher terrain of the plateau will also result in localized
outflow boundaries that will linger across the area overnight. As
WSW/SW 850 mb winds increase late tonight, this will increase
localized convergence along these boundaries with the potential
for isolated to scattered convection during the overnight and
early  Wednesday morning time-frame. Confidence in timing and
location is very uncertain because of these mesoscale boundaries.

Shortwave vort maxima will lower heights across the region on
Wednesday with the potential for increasing coverage of isolated
to scattered showers and thunderstorms. A surface cold front will
shift southeast late in the day through Wednesday night with the
potential for scattered showers and thunderstorms along this
boundary. RAP forecast soundings are indicating MLCAPE of 2000 to
3000 J/Kg across the area on Wednesday with DCAPE of 800 to 1000
J/Kg. PW values will also increase late Wednesday ahead of the
front near 2.0 inches. This will produce a low severe risk with
localized strong wind gusts  in addition to frequent lightning
and heavy rain rates. While not everyone will see abundant rain,
this is expected to be the most widespread convection across the
area in weeks.

&&

.LONG TERM...
(Thursday through next Tuesday)
Issued at 229 PM EDT Tue Jul 16 2024

Key Messages:

1. A frontal passage will keep widespread showers and storms across
the area through Thursday.

2. A break from the heat is expected behind the front, with slightly
below normal temperatures Thursday through Tuesday. Good chances for
rainfall will return late Friday into Saturday and again Sunday
through Tuesday

Discussion:

At the beginning of the extended forecast A cold front will be over
or near the forecast area ahead of a large upper trough moving south
from the northeast states. The big forecast question for the
beginning of the extended forecast is how far south does the frontal
boundary move Thursday. If it is still in the vicinity expect
another day of widespread showers and storms. However, if it pushes
too far south then the bulk of the precip will be to the south and
we will be much drier. NBM POPs suggest the front is still in the
vicinity Thursday so will continue with that trend. Storm total QPF
ending Thursday has most locations around 1 to 1.5 inches of much
needed rainfall.

After Thursday the front will have shifted south but shortwave
energy moving through the upper flow and south to southeast flow off
the Gulf of Mexico will keep a chance of showers and storms in the
afternoon and evening Friday...higher near the mountains. Models
want to bring a surface low along the front into Alabama later
Friday and lift it northward Saturday. As the front lifts back north
through and over the forecast area and eventually remain stationary
Saturday, rain chances increase. The moist flow will keep diurnal
afternoon and evening showers and storms across the region through
Sunday. Rain chances will be highest in the eastern mountains and
lowest northern plateau and Virginia through Sunday. Highs Thursday
through Sunday will be a few degrees below normal and mainly in the
lower 80s northeast to mid and upper 80s central and southwest.

For Monday and Tuesday the frontal boundary lifts farther north into
the Ohio Valley Monday and Tuesday as the Bermuda high stays strong
along the southeast coast. There still should be elevated
precipitation chances due to higher than normal moisture values
across the area. The position of the High pressure area helps Gulf
moisture stream into the southeastern U.S. The convection will be
driven by daytime heating. Temperatures the last two days of the
extended forecast will be slightly below normal during this time.
High temps will generally be in the mid 80s to upper 80s.

&&

.AVIATION...
(00Z TAFS)
Issued at 718 PM EDT Tue Jul 16 2024

Currently, there are showers and storms west of TYS and TRI. It is
unclear if they will hold together and/or make it to the terminals
overnight. The current indications are for them to fall apart with
little impact. Based on this trend, VFR is expected to prevail
with fog development mainly being in places that saw rain
measurable rain today. Shortly after sunrise, there are
indications for additional shower development around TRI that
could create MVFR conditions, but confidence is limited. Through
the afternoon, southwesterly winds are expected with some higher
gusts at TYS and TRI. Late in the afternoon, scattered storms are
likely to approach the terminals, but timing is uncertain.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             76  94  73  89 /  20  80  70  80
Knoxville McGhee Tyson Airport, TN  74  91  71  85 /  50  80  80  80
Oak Ridge, TN                       74  91  71  84 /  40  80  80  70
Tri Cities Airport, TN              71  89  69  80 /  70  90  80  70

&&

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

$$

SHORT TERM...JB
LONG TERM....TD
AVIATION...BW