404 
FXUS64 KMRX 112304 AAA
AFDMRX

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Morristown TN
704 PM EDT Sat Sep 11 2021

.UPDATE...
FOR 00Z AVIATION.

&&

.SHORT TERM...(Tonight and Sunday)

Key Messages:

1. Dry weather expected again tonight and Sunday as upper level 
ridging strengthens over the region and surface high pressure 
remains in control. Temperatures increase back to above normal 
Sunday.

Discussion:

Upper level ridging over the southwest and south central states has 
now begun shifting east and is now covering much of the Tennessee 
Valley. Surface high pressure has now become centered east of the 
Appalachians as well. As a result winds were shifting to the south 
and southwest around the high and rising heights have allowed 
temperatures to climb into the lower 80s at most low elevation 
sites. With light southerly flow overnight lows will be slightly 
warmer tonight...mostly mid 50s to mid 60s. Patchy fog locally dense 
should form across some area rivers and lakes again by early morning 
with slight increase in low level moisture but does not look like it 
will be widespread. A warming trend will continue Sunday as the 
upper high strengthens. Dew points will begin to rise as well from 
the 50s into the lower 60s. Apparent temperatures will be in the mid 
to upper 80s Sunday afternoon with a few spots to about 90. Cloud 
cover should still be scattered and not affect high temperatures.

TD

.LONG TERM...(Sunday night through Saturday)

|Key Messages:

1. Increasingly hot, humid, and mainly dry through Tues.

2. Chances for afternoon/evening showers/storms increase Wed through 
Sat, but temps will remain very warm and humid.

Discussion:

Sunday Night through Tuesday...

Quasi-zonal flow will be found across the country Sun night and Mon 
with H5 heights over 591 DAM over the SE CONUS and broad surface 
high pressure retreating into the western Atlantic. This will 
maintain WAA, and with plenty of sunshine continuing and 850 mb 
temps around 18C, highs Mon will warm into the upper 80's to near 90 
after morning lows staying in the low/mid 60's. By Mon night, a 
potential tropical cyclone will be approaching the TX coast with a 
landfall likely to occur sometime during the day Tues. Mid/upper 
ridging will continue to hang on over the SE CONUS through Tues with 
the broad surface high still over the western Atlantic as well, but 
the southerly flow will begin to advect the tropical moisture from 
the cyclone into the TN Valley. This increase in low-level moisture 
combined with strong heating will allow for isolated diurnal 
convection over the S Valley, Plateau, and Smokies Tues, so blended 
NBM slight chance PoPs. Most areas will stay dry with morning lows 
in the low/mid 60's and highs Tues around 90 once again.

Tuesday Night through Saturday...

The potential tropical cyclone will slowly move into the Delta 
region Tues night and Wed while a northern stream shortwave trough 
progresses rapidly from the N Plains through the Great Lakes. This 
shortwave will push a weak cold front into the OH Valley Wed, but 
the front will quickly wash out as a piece of the shortwave cuts off 
and dives into the S Plains and merges with the tropical system. 
This will result in a slow moving, cut off low that will gradually 
rotate through the Mid South Wed and Thurs advecting deep tropical 
moisture into the TN Valley and S Appalachians beneath large scale 
mid/upper ridging that rebuilds to the north. Have chance PoPs 
areawide both Wed and Thurs for diurnal convection as PWATs should 
be increasing to nearly 2 inches, and this combined with heating 
will build up appreciable diurnal instability. Too early for 
details, but slow moving convection with locally heavy rainfall is 
possible. Uncertainty increases Thurs night through Sat regarding
how fast the cut off low will eject to the NE. The deterministic 
CMC and ECMWF are much more progressive with another northern 
stream shortwave kicking the low northeastward, while the GFS 
keeps it spinning over the deep South as another potential 
tropical system develops in the western Atlantic. The 
GEFS/Euro/Canadian ensemble means show big differences too, so 
kept NBM chance PoPs each afternoon Fri and Sat. Temps from Wed 
into next weekend will remain very warm and humid in this tropical
airmass with highs in the mid/upper 80's and lows in the 
mid/upper 60's.

Garuckas


&&

.AVIATION...
00Z TAF DISCUSSION.

Clear skies are forecast at all sites through the TAF period, but
there is some uncertainty regarding fog at TRI. For now, signs
point to no fog, similar to last night. Dewpoints dropped to the
lower 50s this afternoon, and with forecast lows in the mid 50s,
fog seems unlikely. But it's TRI, so you never know. Could see
quarter mile vis develop if fog rolls in off the nearby lake.

DGS

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             63  88  65  89  67 /   0   0   0  10   0 
Knoxville McGhee Tyson Airport, TN  61  87  65  89  67 /   0   0   0  10   0 
Oak Ridge, TN                       61  86  63  88  66 /   0   0   0  10   0 
Tri Cities Airport, TN              56  86  62  88  63 /   0   0   0   0   0 

&&

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

$$