Severe Thunderstorm Warning 416, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
1235 PM CDT Fri Aug 11 2023

...New SHORT TERM, AVIATION...

.SHORT TERM...
(This afternoon through Saturday)
Issued at 1233 PM CDT FRI AUG 11 2023

Central Alabama is in the wake of yet another upper level
shortwave and associated MCS that developed across northeast
Mississippi just after midnight last night. This MCS was fairly
well forecast by the high-res guidance despite developing a little
later than expected. Nonetheless, strong to isolated severe wind
gusts were observed this morning as the MCS tracked east-
southeastward over the forecast area. Even after storms passed
through our office here at the Shelby County Airport, the 12z KBMX
sounding observed very unstable nocturnal conditions with over
3000 J/kg MUCAPE and 1200 J/kg DCAPE. The old stalled boundary is
currently draped from west to east along a line from Vernon to
Birmingham to Heflin. Very slowly but surely, that boundary will
start to move northward through the evening as the surface ridge
in the central Gulf of Mexico strengthens.

For the near-term, we'll continue to see storms firing with the
stalled boundary still in the area and westerly bulk shear around
25 to 30 knots. Upper level perturbations will continue to provide
enough lift aloft for additional storms through the afternoon,
with water-loaded downdrafts likely within stronger storms.
Looking out the window at the current radar, storms will continue
across eastern counties while we're also expecting additional
storms to fire more to the west closer to the I-65 corridor. Any
additional shortwave activity coupled with leftover outflow
boundaries from previous storms to our west will help trigger
additional convection through this evening.

Other than the isolated severe storm chances, very dangerous heat
will return as a major story through Saturday. We'll stay in a
warm-sector environment with the surface ridge off to our south.
Dewpoints will struggle to mix out due to the the depth of the
moist environment, remaining in the mid to upper 70s. Heat index
values today will easily rise to 105 or above across the western
and southern counties and may rise close to 105 as far north as
Birmingham this afternoon. The Heat Advisory may need to be
expanded northward if we don't see dewpoints mix down a degree or
two from what we're observing currently. Upper level heights are
expected to increase during the day on Saturday as the ridge
builds in from the west. We'll see very dangerous conditions,
perhaps the worst we've seen so far this summer. We'll need an
Excessive Heat Warning over a majority of Central Alabama, as heat
index will rise to 110 degrees or higher.

At least scattered showers and storms will remain possible during
the day on Saturday, with high-res guidance indicating yet another
upper level impulse diving southward around the upper ridge. We'll
have to watch for the potential of another MCS to develop and move
southward through the afternoon. Chance PoPs have been included
areawide for now, until higher confidence in placement of the
storms can be achieved.

56/GDG

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 341 AM CDT FRI AUG 11 2023

Saturday through Monday.

Broad Mid-level ridging will persist over the Four Corners States
while a local maximum will be found over East Texas and much of
Louisiana to start the long term forecast period. Heights look to
rise further over the local area Sunday through Monday followed by
some contraction over the northern portion of the area late
Monday into Tuesday. Expect partly cloudy skies with isolated
showers and thunderstorms mainly in the afternoon hours. The
combination of heat and humidity will result in heat index values
remaining below 105 degrees across portions of the far
northeastern counties with the central counties exceeding 105
degrees while the higher values will be found across our south and
southwest with readings near 110.

Tuesday through Thursday.

Global guidance solutions have come into better agreement of a
closed low over Wisconsin with a longwave trough swinging east
over the Mid Mississippi River Valley Region during this time
frame. The longwave troughing will move further east closer to the
area on Wednesday before a more zonal flow regime returns on
Thursday. A surface cold front is progged to push into the
northern portion of the forecast area on Tuesday, resulting in
scattered showers and storms south and southeast with lower
chances across the northern third of the area. With the zonal flow
regime aloft, the surface front looks to stall just south of the
Interstate 20 corridor on Wednesday and Thursday, resulting in
scattered showers and storms each afternoon near and south of the
boundary with more isolated activity to the north. Heat index
values are expected to exceed 105 degrees on Tuesday across the
southern third of the forecast area. Drier air will mix down on
Tuesday and persist through Wednesday, resulting in heat index
values projected to be below 105 degrees areawide for Wednesday
and Thursday.

05

&&

.AVIATION...
(18Z TAFS)
Issued at 1025 AM CDT FRI AUG 11 2023

Occasional MVFR stratus conditions have been observed across
terminals early this afternoon which should gradually mix out to
VFR. SHRA/TSRA activity has also gradually decreased for northern
terminals. Have kept mention of TEMPO TSRA for MGM and TOI this
afternoon with at least scattered activity expected across
southern Alabama before diminishing this evening. Winds will
remain light from the west except within thunderstorms, where
variable wind gusts will be likely. VFR conditions are expected
through the end of the forecast period.

56/GDG

&&

.FIRE WEATHER...

Scattered showers and storms will continue today through Saturday
with afternoon relative humidity minimums in the 50 percent
range. A decrease in shower and thunderstorm activity is forecast
Sunday and Monday while heat index readings will continue to
exceed 105 degrees during the afternoon hours across much of the
area through this time frame.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     91  73  94  72 /  50  10  40  10
Anniston    91  74  94  73 /  70  10  40  10
Birmingham  92  74  95  75 /  50  10  40  10
Tuscaloosa  93  76  96  75 /  40  20  30  10
Calera      92  74  96  76 /  50  20  40  10
Auburn      90  73  94  75 /  70  20  30  10
Montgomery  96  76  98  77 /  60  30  30  10
Troy        96  76  98  76 /  60  30  30  10

&&

.BMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 9 PM CDT this evening for the following
counties: Barbour-Bibb-Bullock-Dallas-Fayette-Greene-Hale-Lamar-
Lowndes-Marengo-Marion-Montgomery-Perry-Pickens-Pike-Sumter-
Tuscaloosa-Walker-Winston.

&&

SHORT TERM...56/GDG
LONG TERM....05
AVIATION...56/GDG

Hazardous Weather Outlook
National Weather Service Birmingham AL
315 PM CDT Fri Aug 11 2023

ALZ011>015-017>050-122315-
Marion-Lamar-Fayette-Winston-Walker-Blount-Etowah-Calhoun-Cherokee-
Cleburne-Pickens-Tuscaloosa-Jefferson-Shelby-St. Clair-Talladega-
Clay-Randolph-Sumter-Greene-Hale-Perry-Bibb-Chilton-Coosa-Tallapoosa-
Chambers-Marengo-Dallas-Autauga-Lowndes-Elmore-Montgomery-Macon-
Bullock-Lee-Russell-Pike-Barbour-
315 PM CDT Fri Aug 11 2023

This Hazardous Weather Outlook is for the counties served by the
National Weather Service office in Birmingham.

.DAY ONE...Outlook through Tonight.

Severe thunderstorms are possible through 7 pm this evening. The risk
area includes locations near and south of I-20. The main threats will
be damaging winds and large hail.

The combination of high temperatures and high surface dew points will
create a feels like temperature from 105 to 109 degrees today. The
threat area is generally west of I-22 and the US 280 corridor. This
roughly covers the western two thirds of central Alabama.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Severe thunderstorms are possible again on Saturday. The threat
window appears to be from noon to 7 pm for the northeast half of the
area. Please see graphic for specific locations. The main threats
will be damaging winds and large hail.

The hot area today will increase on Saturday. The western area will
have an Excessive Heat Warning where heat indices will be 110 or
greater. The remainder of central Alabama will also increase in the
feels like temperature and a Heat Advisory has been issued.

Heat and humidity will produce dangerous conditions through Tuesday.
Heat indices will be 105 or greater each afternoon in various
locations across central Alabama.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management may be needed
this afternoon and Saturday afternoon.

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