171
FXUS64 KMRX 160523
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
123 AM EDT Tue Jul 16 2024

...New AVIATION...

.UPDATE...
Issued at 900 PM EDT Mon Jul 15 2024

|Late afternoon and early evening storms have ended. Expect partly
cloudy skies south and mostly clear north with patchy fog forming
late. Temperatures this evening are in the mid 80s to around 90
and should cool slowly into the mid 60s northeast to mid 70s
southwest which will not change for morning lows in the update.
Change is to remove showers and storms except a few in eastern
mountains another hour or so. Tuesdays weather looks similar to
todays with isolated to widely scattered showers storms mid
afternoon to early evening in southern areas. Updated forecast
sent.

&&

.SHORT TERM...
(This evening through Tuesday)
Issued at 306 PM EDT Mon Jul 15 2024

Key Messages:

1. Isolated convection again on Tuesday with main coverage across
the south.

2. Continued hot temperatures with mostly dry conditions in the
short term.

Discussion:

Mesoanalysis is showing some areas of around 2000 J/Kg MLCAPE this
afternoon with isolated convection along the higher elevations,
mainly across western higher elevations of the Cumberland Plateau
and Clinch Mountains. Some gusty winds could be expected with the
stronger storms, but severe weather is unlikely. Areas that do
receive rain will have some patchy fog overnight into Tuesday
morning - such as the Sequatchie Valley.

The weak upper level trough/col will shift southeast on Tuesday
with weak southwesterly flow across far southeast Tennessee and
southwest North Carolina. Northwest flow and increased subsidence
will limit convection across the northern zones of our forecast
area with slight chance/chance PoPs across southern/southeastern
counties. MLCAPE will be near 2000 J/Kg according to RAP forecast
soundings with some dry air in the boundary layer keeping LFC
heights relatively high and providing a risk of localized winds
with the strongest pulse convection. Overall, the severe wind risk
is very low.

&&

.LONG TERM...
(Tuesday night through next Monday)
Issued at 306 PM EDT Mon Jul 15 2024

Key Messages:

1. Excessive heat is expected to die down with the passing of a
front and falling of pressure heights throughout the atmosphere.

2. The frontal passage will bring widespread storms across the area
Wednesday into Thursday.  Higher than normal moisture may lead to
scattered showers for the remainder of the period.

Tuesday Night through Thursday Night

The period begins with the continuance of a ridging pattern for our
region, with a high pressure center located off the Atlantic Coast.
The shortwave trough to our southwest has been cut off and seems to
be drifting as a low pressure center further south throughout the
period.  Ridging is ended by a frontal passage and a return to a
troughing pattern by Thursday.  The timing of the frontal passage is
uncertain, but it seems to move into the area by Thursday night. The
ECMWF brings the front through our area quicker and a tad further
south than the GFS. Surface temperatures are expected to exceed 90
degrees once again on Wednesday, with heat indices likely to exceed
100 degrees due to increased humidity.

The frontal passage is proceeded by a stark rise in PWATs, with
values around 1.9 inches.  The majority of our region is under the
WPC marginal risk for excessive rainfall due to the higher than
average moisture.  Wind profiles signal the potential for training
convection which could lead to some higher rainfall amounts in
areas.  Overall, MLCAPE values will be near or below 1000 J/kg for
much of the region, with the some localized higher values. Deep
layer shear is unimpressive ahead of the front but rises with its
passage, potentially leading to higher rainfall amounts on Thursday.
With this event, the potential of flooding is in question, however
we can expect the ongoing lack of precipitation to lower that
potential. The main risk of these storms is going to be locally
strong wind gusts.

Friday through Monday

We can expect the frontal boundary to linger over the area for the
remainder of our period after its initial passing.  The GFS and
ECMWF signal a drop in pressure heights following the frontal
passage, which could lead to a break from the excessive heat.  While
temperatures are likely to lower, PWATS remain unseasonably high,
which will allow weak instability to persist.  Precipitation is
likely during this period and will be mostly diurnally driven and
not unlike most summertime convection.  The southeastern ridge
strengthens towards the end of our period, however moisture remains
quite high for the time of year.

&&

.AVIATION...
(06Z TAFS)
Issued at 121 AM EDT Tue Jul 16 2024

VFR conditions are expected through the 06Z TAF cycle. Isolated to
weakly scattered showers and a thunderstorms will develop across
the region tomorrow afternoon. This will result in a low but non-
zero potential for lightning near or atop a terminal for a brief
period of time. Given the low confidence, have continued this as a
prob30 mention at this time.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             96  76  95  72 /  30  20  80  60
Knoxville McGhee Tyson Airport, TN  96  75  93  72 /  30  30  80  80
Oak Ridge, TN                       95  74  93  71 /  20  30  80  80
Tri Cities Airport, TN              93  72  91  69 /  20  30  80  80

&&

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

$$

SHORT TERM...TD
LONG TERM....BW
AVIATION...KRS