-- Discussion containing changed information from previous version are highlighted. --
467
FXUS64 KMRX 171744
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
144 PM EDT Mon Jun 17 2024

...New AVIATION...

.UPDATE...
Issued at 1145 AM EDT Mon Jun 17 2024

A late morning update to lower rain chances slightly and with a
little less coverage over NE TN and delay main rain chances to
start in early afternoon. Not much other changes as upper level
ridge holds tight over the Carolinas. The latest NAM model and NBM
data are pretty aggressive with showers and thunderstorm chances
this afternoon to about 00Z for the northeast half of the region.
Expecting convection to develop first in the NE TN mountains and
move slowly into the valleys. PW values are around 1.6 inches so
could have heavy rainfall in some storms. MLCAPE values still are
around 1500 J/KG with DCAPE values from 600 to 1000 J/KG so some
downburst potential with any thunderstorms. Updated forecast sent.

&&

.SHORT TERM...
(Today and tonight)
Issued at 341 AM EDT Mon Jun 17 2024

Key Messages:

1. Hot and humid again today with upper ridging across the region.

2. Afternoon scattered showers and thunderstorms possible, mainly
across the mountains.

Discussion:

It will be hot and humid once again with a 500mb 595dam ridge centered
over central North Carolina. Subsidence will result in mostly dry
conditions and some areas of lower dewpoints. Current CAM guidance
suggests lower afternoon dewpoints in the Chattanooga/southern
valley region in the wake a weak shortwave feature and downslope
850mb flow. This will result in sub-500 J/Kg MLCAPE across the
southern valley which will limit thunderstorm chances; however,
MLCAPE values of 1500 to 2000 J/Kg are expected across the East
Tennessee mountains through northeast Tennessee where higher
moisture and slightly better ascent is expected. Boundary layer
winds are weaker in these areas and less downslope flow is
anticipated. Convection will likely develop across the mountains
and drift northward through the evening before dissipating between
22z-01z. With PW values around 1.7 inch, some heavy rain rates
could be anticipated with thunderstorms. Additionally, severe
weather is unlikely, but DCAPE values across the mountains through
northeast Tennessee will max out around 900 to 1000 J/Kg which
will be sufficient for some strong downburst winds associated with
pulse convection. Localized fog will be expected tonight where
rain occurs during the afternoon.

&&

.LONG TERM...
(Tuesday through Monday)
Issued at 341 AM EDT Mon Jun 17 2024

Key Messages:

1. Hot and dry conditions will continue through the week with highs
in the 90s across most of the area.

2. By the weekend, low-end chances for storms return, along with
potentially more dangerous heat and humidity.

Tuesday through Thursday

At the start of the period, upper-level ridging will be building in
with a 500mb high to near 5,950m. A strong surface high will also be
centered over the Atlantic. With drier air advecting from the east
and weak southeasterly flow over the mountains, hot conditions will
continue with nearly zero rain chances. The drier air will also
suppress humidity, keeping heat index values close to the air
temperatures. By Wednesday, ridging will continue to strengthen with
the 500mb high nearing a record 6,000m over the northeast and
heights locally near 5,960m. Similarly hot conditions can be
expected with even drier air arriving from the east. By Thursday,
500mb heights will rise even more over our area to above record-high
values per BNA sounding climatology. This strongly suggests
temperatures rising far into the 90s, especially in the southern
Valley. Continued surface high pressure and dry air will keep rain
chances out of the forecast.

Friday through Sunday

By Friday, we start to see a breakdown in high pressure and a steady
increase in moisture through the weekend. While 500mb heights will
drop closer to 5,920m, temperatures at the 850mb level are indicated
to be near-record high values of 21 to 22 Celsius. The increase in
moisture will be sufficient for a return in low-end PoPs, especially
by the end of the weekend. However, the more notable impact will be
the increase in humidity and overall heat index values, likely in
excess of 100 degrees. This will be dependent on the development and
coverage of diurnal convection, but indications suggest heat above
and beyond the first half of the extended period.

&&

.AVIATION...
-- Changed Discussion --
(18Z TAFS)
Issued at 130 PM EDT Mon Jun 17 2024

VFR conditions prevailing today with scattered showers and
thunderstorms already developing near TYS and TRI early this
afternoon. Will keep vicinity TSRA and tempo groups for storms,
the next few hours. Convection should end about sunset with
patchy fog developing late tonight, especially near TRI. Winds
will stay light except in any convection.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
Chattanooga Airport, TN             74  91  71  90 /  10   0   0   0
Knoxville McGhee Tyson Airport, TN  71  91  68  89 /  10   0   0   0
Oak Ridge, TN                       71  91  69  89 /  10  10   0   0
Tri Cities Airport, TN              68  90  64  89 /  10  10   0   0
-- End Changed Discussion --

&&

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

$$

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