Special Weather Statement, NWS Huntsville, AL

Area Forecast Discussion
National Weather Service Huntsville AL
1050 AM CDT Sat Jul 1 2023

...New NEAR TERM...

.NEAR TERM...
(Rest of Today)
Issued at 1050 AM CDT Sat Jul 1 2023

Scattered showers and thunderstorms are continuing to develop over
western Tennessee and move east through westerly to southwesterly
flow. Some of these storms have been severe. This is all forming
along a boundary and associated weak shortwave trough axis that is
rotating around a meso-high centered over central and southern
Alabama and Lousiana. Temperatures with clear skies earlier this
morning have climbed into the upper 80s to around 90 degrees in
northwestern Alabama. Further east, temperatures are in the mid to
upper 80s. Some mixing earlier this morning made things a bit more
bearable east of the I-65 corridor. However, as this shortwave
moves further east across central Tennessee and northern Alabama
over the next 2 to 4 hours, expect shower and thunderstorm
activity to develop over the area and excessive heat to develop.

A very unstable airmass is in place ahead of this shortwave.
MUCAPE and SBCAPE between 3000 and 5000 J/KG is building ahead of
it. Mid level lapse rates are very steep around 7.5 degrees/km,
which should aid in strong to severe hail development. Plenty of
dry air aloft should aid with good low level moisture in
microburst potential in producing strong to severe microbursts as
well.

An excessive Heat Warning still looks good based on the high
dewpoints expected ahead of the shortwave and high in the mid to
upper 90s near and west of the I-65 border. Further east, lower
high temperatures and slightly lower dewpoints will keep heat
indices a bit lower, but still reaching heat advisory criteria of
105 to 109 degrees.

&&

.SHORT TERM...
(Tonight through Monday)
Issued at 330 AM CDT Sat Jul 1 2023

On Sunday, the ridge will be shunted farther to the south as a
trough makes headway into the OH Valley and Grt Lakes regions.
Increasing synoptic scale lift will support more organized and
potentially widespread convection in the TN Valley region, but
there continues to be uncertainty with regards to exact placement
and timing for convection. Steep low-lvl lapse rates and
inverted-V soundings on Sunday, along with high PWs (>1.7 in)
suggest a threat for strong outflow winds with thunderstorms. It
does appear that once again, convection may be delayed
sufficiently late for temp rises in the presence of lingering high
TDs to generate heat indices above 105 F in many areas. Thus, a
Heat Advisory has been issued for the entire forecast area for
Sunday.

Given the prospects for a stalled sfc front near and probably just
to the north of the area, along with continuing short waves
transiting eastward across the area, Monday may offer generally
cloudier/showery weather. POPs around 50-60% were included for all
areas for the afternoon period.

&&

.LONG TERM...
(Tuesday night through Friday)
Issued at 330 AM CDT Sat Jul 1 2023

Unsettled weather should continue for the greater part of the
Independence Day work week, as a more zonal upper flow becomes
established over the SE Lower-48. A very moist lower atmosphere
however will remain, with forecast dewpoints remaining in the lower
to at times mid 70s through the latter portion of the new week.
This moisture and associated precipitable water amounts ranging in
the 1.5 to 2.1 inches (especially the mid and latter half of the
week). This moisture plus daytime heating produced instability
will result in scattered (~25-55%) to numerous (~55-75%) shower
and thunderstorm chances, especially each afternoon and early
evening.

The amount of moisture in the low/mid atmosphere as seen in forecast
soundings would suggest more clouds than sun for much of the period.
Despite that, some sun should break through in the morning to early
afternoon and help raise high temperatures into the lower 90s for the
Tue/Thu time frame. For July 4th, the best time for shower and
thunderstorm activity should be in the afternoon and early evening.
Highs should rise to seasonably warm levels into the lower 90s. Rain
chances should diminish in the evening with a loss of heating and a
more stable environment, with lows by daybreak Wednesday into the
lower 70s. A similar forecast is expected for Wed and Thu with highs
into the lower 90s, with numerous showers/storms in the afternoon to
early evening.

&&

.AVIATION...
(12Z TAFS)
Issued at 640 AM CDT Sat Jul 1 2023

VFR conditions currently are likely to prevail through the
morning, but isolated to scattered SHRA/TSRA may occur in the
area this afternoon. Uncertainty in coverage, location and timing
of activity this afternoon is still affecting forecast
confidence. With only scattered convection forecast, PROB30 groups
were used to address threat of SHRA at KHSV and KMSL TAF sites
after 21Z.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Excessive Heat Warning until 8 PM CDT this evening for
     ALZ001>007-016.

     Heat Advisory from 8 PM this evening to 8 PM CDT Sunday for
     ALZ001>007-016.

     Heat Advisory until 8 PM CDT Sunday for ALZ008>010.

TN...Excessive Heat Warning until 8 PM CDT this evening for TNZ076-
     096.

     Heat Advisory from 8 PM this evening to 8 PM CDT Sunday for
     TNZ076-096.

     Heat Advisory until 8 PM CDT Sunday for TNZ097.

&&

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

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