Heat in Tennessee, August 11, 2023

Area Forecast Discussion
National Weather Service Huntsville AL
1240 PM CDT Fri Aug 11 2023

...New AVIATION...

.NEAR TERM...
(Rest of Today)
Issued at 1001 AM CDT Fri Aug 11 2023

Given instability already in place driven by dewpoints in the mid
to upper 70s and temperatures in the upper 70s to lower 80s
across northern Alabama, cannot rule out a 20 to 30 percent chance
of a shower or thunderstorm developing in northeastern Alabama SW
towards Cullman county through 3 PM. In those areas, some weak
convergence lingers behind the convection that pushed southeast of
the area around daybreak. This is helping to keep that area a bit
more cloudy this morning.

The highest dewpoints are mainly near the AL/MS border (75 to 80
degrees). Expect that to continue at least to around 1 PM and then
possibly remain in the mid to upper 70s afterwards. More prolonged
clearing can be seen in portions of NW AL and this has allowed
temperatures to climb into the lower to mid 80s already in that
area. Given the old rule of adding ten degrees and 10 AM combined
with model data holding off on appreciable increases in cloud
cover until around 2 or 3 PM, think that highs could reach the
lower 90s in NW Alabama. With dewpoints already mentioned,
thinking this will allow heat index values to climb to between 105
and 109 degrees for 3 hours or more towards noon into the early
afternoon hours. We could see increasing cloud cover and more
scattered shower/thunderstorm activity briefly from Franklin
county SE into Cullman county as the eastern extent of the MCS
currently over SE Arkansas brushes the AL/MS border, but this will
likely happen around or after 3 PM. Increased highs slightly in
NW AL given ongoing lack of cloud cover there, but kept highs
near/east of the I-65 corridor in the 85 yo 90 degree range. This
should keep heat index values below 105 degrees near and east of
these areas. A Heat Advisory has been issued for Lawrence,
Franklin, Colbert, and Lauderdale counties from 11 AM through 7
PM.

&&

.SHORT TERM...
(Tonight through Sunday)
Issued at 345 AM CDT Fri Aug 11 2023

The upper ridge over the southern Plains looks to drift slightly
to the east tonight into the upcoming weekend period. While upper
waves may continue to traverse along/east of the ridge pattern,
the location/timing of these features remain very uncertain. The
wx pattern tonight at least looks fairly benign, as the stalled
front weakens/lifts to the north. This may allow for some patchy
fog early Sat morning. Overnight lows look to fall mainly into the
upper 60s/lower 70s, before temps rebound into the lower 90s/near
90F later in the day Sat. Low chances (20-30%) for showers/tstms
are expected Sat afternoon with the potential for one of these
upper disturbances moving across the area. Low chances (10-20%)
for showers/tstms continue Sat night into Sun morning north of
the TN River, in closer proximity to additional passing upper
waves. Sct showers/tstms are possible Sun afternoon, aided once
again by passing upper waves coupled with diurnal heating. Lows
Sat night look to fall more into the lower/mid 70s, before temps
once again rebound into the lower 90s/near 90F Sun afternoon. Max
heat indices on Sun also look to approach 105-107F in some spots
and a Heat Advisory may be warranted later this weekend.

&&

.LONG TERM...
(Sunday night through Thursday)
Issued at 345 AM CDT Fri Aug 11 2023

A seemingly persistent and disturbance laden upper level flow
that has helped continue a parade of showers and thunderstorms
across the area this past week, appears to become oriented a bit
further more to our north next week. This should actually bring
drier conditions to the Tennessee Valley for a portion of next
week. Before then, this period will begin on a very warm to hot
note Monday. Mon morning should start out muggy with lows in the
mid 70s. A hot and humid airmass still in place (dewpoints in the
mid/upper 70s) along with highs in the low/mid 90s will create
heat index values into the 100 to 109 degree range for a good
portion of the area. The higher end of this range (105-109
degrees) is in our Heat Advisory criteria.

A cold front that should be situated to our north late Sunday,
should move to the SE, and across the Valley Mon evening. This will
help end the heat, humidity and rain chances, with lows by Tuesday
morning cooling into the mid 60s to around 70. Highs that day will be
noticeably more comfortable for most, mostly in the mid 80s. Lows
Tue night will cool into the lower 60s. Similar conditions are
forecast on Wednesday with highs in the mid 80s and lows mid 60s. A
return of moisture mainly over areas near and south of the Tennessee
River will bring a slight chance of showers and thunderstorm Thursday
afternoon. Highs should warm into mid/upper 80s, and lows in the
mid/upper 60s.

&&

.AVIATION...
(18Z TAFS)
Issued at 1240 PM CDT Fri Aug 11 2023

VFR conditions are expected much of the TAF period. With light
winds and mainly high cloud cover expected, some MVFR VSBYS could
develop near fog development. Then expect VFR conditions to return
after 13Z. Any -TSRA was left out of TAFs for now due to low
confidence of occurrence until after the TAF period.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Heat Advisory until 7 PM CDT this evening for ALZ001>004.

TN...None.
&&

NEAR TERM...KTW
SHORT TERM....09
LONG TERM....RSB
AVIATION...KTW