Heat in Tennessee, August 16, 2024

Area Forecast Discussion
National Weather Service Huntsville AL
107 PM CDT Fri Aug 16 2024

...New NEAR TERM, SHORT TERM...

.NEAR TERM...
(Tonight)
Issued at 106 PM CDT Fri Aug 16 2024

Active afternoon of weather is on tap for the Tennessee Valley as
a cold front approaches the area from the north and west. This
feature will serve as a lifting mechanism for showers and
thunderstorms later this afternoon and into the early portions of
the evening hours. Good heating this morning has warmed
temperatures into the low to mid 90s as of 18z and they will
continue to climb another 2-4 degrees this afternoon. SBCAPE
values of 2500-3500 J/kg have evolved, with no capping inversion.
Mid-level dry air and an inverted-v sounding profile would favor
an environment favorable wet microbursts or line segments (though
bulk and effective shear values remain fairly modest and around
20-30 kts at most). Main timing of this still appears to be 19-01z
this evening, with PoPs generally in the medium category (40-60%)
through 01-02z. Precipitation chances will wane quickly with the
setting sun, but would think that cloud cover may be slower to
clear this evening, resulting in a mostly cloudy sky. Some partial
clearing may allow for localized patchy fog in areas that see
locally heavier downpours. Otherwise, it'll just be a warm/humid
night with lows in the mid 70s.

&&

.SHORT TERM...
(Saturday through Monday)
Issued at 106 PM CDT Fri Aug 16 2024

We remain in an active pattern as the cold front will be slow to
move across the Tennessee Valley and another shortwave rotates
around the parent low over the meandering over Great Lakes. Hi-Res
guidance continues to highlight the next impulse and associated
convection to move through the region mid/late morning into the
early afternoon (14-18z). Instability parameters won't be quite as
high given the morning cloud cover, but would anticipate at least
1000-2000 J/kg of SBCAPE to go along with 20-30 kts of bulk
shear, allowing for a marginal threat for a few strong to severe
storms. Low confidence in an additional round of convection late
Saturday afternoon and evening -- all dependent on the timing of
the first round and how quickly we can recover.

The aforementioned boundary will sag further to the south into
central Alabama on Sunday, but with yet another shortwave
traversing the area, low to medium chances (20-40%) for afternoon
showers and storms seemed warranted once again. A few of these
storms could be locally strong to severe during the peak heating
of the afternoon. The upper trough will pivot into the central
Appalachians and Mid Atlantic on Monday, with northerly flow
ushering in a cooler and drier air mass bringing an end to the
rain chances and a break from 90s temperatures as highs Monday
will only peak in the mid to upper 80s.

&&

.LONG TERM...
(Sunday through Thursday)
Issued at 357 AM CDT Fri Aug 16 2024

Consensus guidance from the 16/00Z suite of global models suggests
that a mid-level longwave trough will become established across
eastern North America early in the period, with moderately strong NNW
flow aloft predicted to remain in place across the TN Valley through
the middle of next week. At the surface, an area of low pressure
will shift east-northeastward across southern Quebec and into western
New England on Sunday/Sunday night, with the trailing cold front
expected to cross the CWFA at some point Sunday afternoon. Thus, a
low-medium (20-40%) chance for showers and a few thunderstorms has
been maintained in the grids through late Sunday morning. Although
some wrap-around stratus clouds may impact the northeastern portion
of the region on Sunday night/Monday (in the wake of the departing
cyclone), probabilities for any light rain showers or sprinkles
remain very low (5-10%). Light-moderate N-NE flow will advect a
cooler/drier continental airmass southward early next week, with
highs falling into the m-u 80s for most of the region beginning
Monday, and lows dropping into the u50s-l60s Tuesday morning (and
perhaps m-u 50s Wednesday morning). Present indications are that low-
level ESE flow will return Wednesday night as a subtle surface trough
retrogrades westward across the region, and this will allow for a
minor increase in both low-level moisture and chances for showers on
Thursday.

&&

.AVIATION...
(18Z TAFS)
Issued at 1202 PM CDT Fri Aug 16 2024

A front will bring SHRA/TSRA to the area this afternoon which may
result in MVFR to localized IFR conditions between 19-00z (have
handled this with a TEMPO mention for now). AWWs and amendments
may be needed during this timeframe. Convection will wane after
sunset, but MVFR ceilings may persist for much of the night.
Saturday morning, a second round of TSRA may push through the
area and have added a PROB30 to account for this.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Heat Advisory until 5 PM CDT this afternoon for ALZ001>007-016.

TN...Heat Advisory until 5 PM CDT this afternoon for TNZ096.

&&

NEAR TERM...AMP
SHORT TERM....AMP
LONG TERM....70
AVIATION...AMP