028
FXUS64 KMRX 051804
AFDMRX

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

...New AVIATION...

.UPDATE...
Issued at 1130 AM EDT Fri Jul 5 2024

Line of showers and thunderstorms are moving onto the plateau
late this morning and are whats left of an MCS that was moving
across middle TN earlier this morning. Our airmass is moist and
unstable with mixed layer CAPE values are 1500 to 2500 J/KG ahead
of the convection. Precipitable water values are very high too 1.7
to 2.2. Dew points are in the mid 70s. The flow is weaker but
scattered to numerous showers and storms are expected to develop
with a risk for damaging wind gusts and wet microbursts. A slight
risk for severe storms was added to the day 1 outlook across NE TN
and SW VA. With warnings issued already in eastern KY there could
be some by early to mid afternoon across northern sections. Late
morning temperatures are in the upper 80s to lower 90s already and
heat index values are in the mid 90s to just over 100. Expecting
highest heat index values next couple hours ahead of the
thunderstorms. A few locations in the central and southern valley
will like reach around 105 heat indexes. Have updated rain
chances to lower them slightly to around 70 percent with line and
increased dew points slightly. Updated forecast sent. May need to
update again as more storms develop at early afternoon.

&&

.SHORT TERM...
(Today and tonight)
Issued at 303 AM EDT Fri Jul 5 2024

Key Messages:

1. Scattered to numerous showers and thunderstorms expected today
ahead of a cold front. Marginally severe storms are possible,
mainly in the afternoon.

2. Another hot, humid day is expected today but with increasing
cloud cover and rain chances, we are not expected to reach Heat
Advisory criteria.

3. Some fog development is possible tonight in locations that
received rainfall.

Discussion:

A trough is moving into the Midwest. Weak troughing will be over
the Tennessee Valley today and tonight. At the surface, a cold
front will move through the region late tonight or early Saturday
with a shift to northerly winds. POPs start to increase late this
morning but the best chance for showers and thunderstorms will be
this afternoon and evening. NBM guidance seems to be running high
on POPs compared to the HREF but this latest run is a little
closer. HRRR guidance has more activity north of I-40 and along
the mountains. With good instability (CAPE over 2000 J/kg) and
plenty of low level moisture in place, there will be a marginal
risk for severe storms mainly in the afternoon during max heating.

With increasing clouds and rain chances, Heat Advisory criteria
will likely not be reached today. Although, it will be hot and
humid with heat indices around 100 for much of the Southern
Valley with highs in the lower 90s and dew points in the mid 70s.

Some showers and storms may linger into the evening hours but
mostly dry weather is expected after midnight. Fog development is
possible but will likely be limited to places that receive rain.

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 303 AM EDT Fri Jul 5 2024

Key Messages:

1. Not quite as hot, but still slightly above normal through much of
the long term.

2. Mostly dry conditions expected across of the area this weekend in
the wake of a front Friday night into Saturday morning.

3. Diurnal showers and thunderstorms increase early next week
especially across the higher elevations.

Discussion:

In general throughout the entire extended, trend PoPs lower each day
compared to NBM guidance and deterministic models due to the drought
conditions developing over much of the area. Also, overall chances
of convection have been too high by ensembles and deterministic
models.

For Saturday, frontal boundary moves east of the Appalachians with
drier air advecting into the region. Any chance of convection will
be confided mainly over the far east Tennessee mountains and
southwest North Carolina. NBM probabilities remain highest there for
measurable rainfall.

For Sunday, ridge of higher theta-e remain across the southern
Appalachian mountains, especially over the Carolina`s. A low chance
of convection is expected over the far east Tennessee Mountains and
southwest North Caroline but overall dry conditions.

For Monday, boundary layer flow becomes more southeast/southerly
allowing for moisture return with theta-e ridge axis pulling into
east Tennessee. Better chance of diurnal convection especially for
the Mountains and Plateau as forcing orographic.

For Tuesday, Wednesday and Thursday, diurnal orographically forced
convection will continue. Continue to believe that the NBM PoPs are
too high due to the aforementioned above. There is a potential by
Thursday that some of the moisture from BERYL may move into the
Tennessee valley.

&&

.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             74  92  72  95 /  50  20  10  10
Knoxville McGhee Tyson Airport, TN  74  90  69  92 /  60  20  10  10
Oak Ridge, TN                       72  90  68  92 /  50  10   0  10
Tri Cities Airport, TN              71  87  67  90 /  70  30  10  10

&&

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

$$

SHORT TERM...TD
LONG TERM....DH
AVIATION...TD