382
FXUS64 KMRX 051940
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
340 PM EDT Fri Jul 5 2024

...New SHORT TERM, LONG TERM...

.SHORT TERM...
(This evening through Saturday)
Issued at 330 PM EDT Fri Jul 5 2024

Showers and thunderstorms have been moving across much of the
forecast area this afternoon. With the moist and unstable airmass
with mixed layer CAPE values 1500 to 2500 J/KG ahead of the
convection some strong storms have occurred. Precipitable water
values continue to be very high 1.9 to 2.2. Dew points ahead of
the convection were in the mid 70s and heat index values have
reached around 105 in a few locations. With the temperature drop
behind the storms heat index values have dropped.

The risk for more storms is now lower because of the cooling with
the remaining threat just the far eastern part of the forecast
area the rest of the afternoon. Highest rain chances will be this
afternoon, then decreasing this evening and overnight. For tonight
the front over middle TN will move across this evening and into
early Saturday. Slight chance to chance showers/storms extreme
east. Lows tonight will still be warm in the lower to mid 70s but
cooler than this morning. Also patchy fog will form in the areas
with significant rainfall. Saturday with upper ridge to the south
and upper trough moving in temperatures will be cooler in the
upper 80s to lower 90s. Lower dew points will be observed by all
with the numbers in the mid to upper 60s so heat index values will
only be in the lower to mid 90s. With the front close to the
mountains a few showers and storms my form but likely move quickly
east of the Appalachians.

&&

.LONG TERM...
(Saturday night through next Friday)
Issued at 330 PM EDT Fri Jul 5 2024

Key Messages:

1. Mostly dry conditions continue into Sunday.

2. First half of next week looks fairly active, so confidence is a
little higher for better afternoon thunderstorm coverage each day.

Discussion:

The Tennessee valley and southern Appalachian region will remain
situated beneath southwesterly flow aloft for much of the long term
period, with troughing over the mid-Mississippi and Ohio valleys and
ridging off the southeast coast. In general, this will mean chances
for diurnally driven showers and thunderstorms most everyday from
Monday onward, with the best chances over higher terrain as is usual
in the summer.

We`ll be in a dry air advection regime Sat night, but by Sun morning
low level flow will begin to turn out of the southeast and bring
some better moisture content back our direction from the Carolinas.
Upslope flow into the southern Appalachians will likely be enough
for at least some isolated convection in the mountains so will keep
some slight chance PoPs through the morning hours in TN mountains
zones. Coverage should increase Sun afternoon with steering flow
pushing storms off into the lower elevations...but the best chances
will remain in the mountains. Don`t drop rain chances Sunday night
as the pattern could support some nocturnal convection, but coverage
should be limited.

Monday through the midweek time frame should see notably higher rain
chances, with southeast/southerly boundary layer flow allowing for
moisture return with theta-e ridge axis pulling into east Tennessee.
Best chance of diurnal convection will remain in orographically
favored mountains and plateau zones on Monday and Tuesday, but
outflow boundary interactions and steering flow pushing storms off
the Appalachians should yield fairly decent rain chances most
everywhere. By Wednesday and Thursday, persistent southwest flow and
the possibility of moisture associated with Beryl being siphoned off
and shot this direction should lead to a steady increase in
afternoon convective coverage.

&&

.AVIATION...
(18Z TAFS)
Issued at 155 PM EDT Fri Jul 5 2024

VFR conditions are expected outside of thunderstorms today.
Showers and storms moving through terminals now will exit next
hour or two but more could form through early evening ahead of a
cold front to the west. Initial storms could have gusty winds to
30 knots or higher at TRI so have Tempo there. Later storms
weaker but still possible MVFR conditions with rainfall and linger
until around 01Z. Some fog/low CIGs will be possible late tonight
at TYS and TRI so included brief MVFR ceiling early Saturday
before VFR again.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             75  93  72  94 /  40  10  10  30
Knoxville McGhee Tyson Airport, TN  73  91  70  92 /  50  10  10  30
Oak Ridge, TN                       71  92  69  93 /  30  10   0  20
Tri Cities Airport, TN              71  89  67  90 /  50  10  10  30

&&

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

$$

SHORT TERM...TD
LONG TERM....CD
AVIATION...TD