Special Weather Statement, NWS Huntsville, AL

Area Forecast Discussion
National Weather Service Huntsville AL
302 PM CDT Sat Aug 21 2021

.NEAR TERM...(Tonight)
Issued at 302 PM CDT Sat Aug 21 2021

It took a while, but storms from W Mid TN this morning have finally
advanced into N AL. Instead of backbuilding over the same area as
they did to the NW, the storms are now much more progressive, but
still capable of producing up to 1 inch/hour per latest MRMS/radar
estimates. Lighting has also generally decreased in frequency; the TN
Valley has been shrouded in low clouds all morning except for
western portions of the area (Tupelo reached 89, MSL reached 85,
while HSV has only reached 77). Precipitable water estimates from
satellite remain in the 2-2.25 inch range.

This morning's 12Z HRRR (and several other CAMs) handled things
fairly well so far today. They suggested an initial round of semi-
organized showers/storms in the late morning-early afternoon
(verifying so far), with a 2nd round in the early evening (generally
00-03Z) expected to develop within the highly unstable airmass to
the west. Satellite trends show bands of building cumulus in that
area, and some clearing already underway over southern Tennessee
suggests that destabilization is still possible. So forecast PoPs
will peak in that 00-03Z period, then taper off rapidly as the mid-
level impulse swings to the SE. Forecast soundings suggest cloud
cover should improve after about 06Z. Although clearing looks
unlikely, this may still be enough to allow for some fog formation
towards daybreak.

.SHORT TERM...(Sunday through Monday)
Issued at 302 PM CDT Sat Aug 21 2021

Another mid-level shortwave will round the SW flank of the eastern
CONUS trough late tonight into early Sunday, and should move across
the TN Valley during peak heating. There should be less moisture
available (PWats expected to be 1.5 to 2.00 inches rather than north
of 2.00) so coverage should be more limited than today, but there
should still be enough to produce at least scattered storms. The
shortwave should clear the area by Sunday evening, and ridging will
begin building in behind it, likely putting an end to this unsettled
pattern.

A ~594 dam upper high will develop over the Ark-La-Tex region by
Monday afternoon, bringing drier air and more substantial subsidence
to the region. PWats will drop all the way to ~1.25 inches, but this
will allow for the heat to return. High temperatures Monday should
easily reach the low-mid 90s (and there is a chance the blended
guidance is a couple degrees too low). When combined with mid-70s
dewpoints, heat index readings should rise to around 100 degrees.

.LONG TERM...(Monday night through Friday)
Issued at 302 PM CDT Sat Aug 21 2021

Mid-level ridging will persist over the central Plains for early-mid
week, keeping the TN Valley mostly dry, seasonably hot, and very
humid. Dew points will stay in the mid 70s as highs hit the low- mid
90s again Tuesday.

That pattern breaks down quickly. A weak circulation will come
ashore from the SE coast Thursday morning, but increasing moisture
(PWats migrating back toward 2 inches) and diminishing subsidence
will be enough to bring PoPs back into the forecast as soon as
Wednesday. NBM PoPs are reasonable for this timeframe for now, but
additional adjustments are likely as the effects of this low become
more apparent. Temperatures will fall a few degrees from their early-
week peak, but will still remain seasonable for late August.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1228 PM CDT Sat Aug 21 2021

An organized cluster of storms will affect KHSV around 18Z; KMSL will
be on the western fringe of the cluster but could still see enough
lightning to affect the terminal. Lightning could continue thru 20Z.
After that, confidence decreases in direct impacts; there will likely
be at least a small break with mostly VFR conditions and additional
scattered SHRA/TSRA later in the afternoon. Confidence is not high
enough to include a TEMPO, only a long-duration VCTS. Rain chances
fall after sunset and particularly after 06Z. If any clearing is
able to occur, fog may become an issue towards daybreak.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

NEAR TERM...BCC
SHORT TERM...BCC
LONG TERM...BCC
AVIATION...BCC

For more information please visit our website
at weather.gov/huntsville.

Hazardous Weather Outlook
National Weather Service Huntsville AL
1151 AM CDT Sat Aug 21 2021

ALZ001>010-016-TNZ076-096-097-220800-
Lauderdale-Colbert-Franklin AL-Lawrence-Limestone-Madison-Morgan-
Marshall-Jackson-DeKalb-Cullman-Moore-Lincoln-Franklin TN-
1151 AM CDT Sat Aug 21 2021

This Hazardous Weather Outlook is for north central Alabama,
northeast Alabama, northwest Alabama and southern middle Tennessee.

.DAY ONE...This afternoon and tonight.

Showers and thunderstorms will continue on and off through this
afternoon and evening. The main hazard will be localized flash
flooding, but damaging winds will also be possible with stronger
storms.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Isolated to scattered thunderstorms are forecast Sunday. Additional
chances for afternoon and evening showers and thunderstorms will
return Wednesday through Friday.

Temperatures will increase early next week with humidity remaining
elevated. This combination will lead to maximum heat index values of
around 100 degrees, especially along and west of Interstate 65.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management personnel is
not anticipated at this time.

Special Weather Statement
National Weather Service Huntsville AL
309 PM CDT Sat Aug 21 2021

ALZ016-212100-
Cullman AL-
309 PM CDT Sat Aug 21 2021

...A strong thunderstorm will impact portions of southwestern Cullman
County through 400 PM CDT...

At 309 PM CDT, Doppler radar was tracking a strong thunderstorm over
Smith Dam, or 11 miles northeast of Jasper, moving east at 25 mph.

HAZARD...Winds in excess of 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Hanceville, Good Hope, Dodge City, Colony, Wilburn, Bremen,
Arkadelphia, Black Bottom and Smith Lake.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

If on or near Smith Lake, get out of the water and move indoors or
inside a vehicle. Remember, lightning can strike out to 10 miles
from the parent thunderstorm. If you can hear thunder, you are close
enough to be struck by lightning. Move to safe shelter now! Do not
be caught on the water in a thunderstorm.

&&

LAT...LON 3389 8701 3390 8710 3392 8708 3399 8715
      3399 8711 3408 8711 3412 8676 3400 8675
      3395 8679 3396 8682 3393 8686 3394 8688
      3392 8689 3391 8692 3387 8692 3386 8696
      3386 8699
TIME...MOT...LOC 2009Z 271DEG 23KT 3394 8710

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

Kula

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