369
FXUS64 KBMX 082013
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
313 PM CDT Wed May 8 2024

...New LONG TERM...

.SHORT TERM...
(This evening through Thursday)
Issued at 122 PM CDT WED MAY 8 2024

Key Messages:

- Isolated showers and some thunderstorms this afternoon and
  evening, a few strong storms may develop.
- A Mesoscale Convective System dives southeast into the area
  after midnight tonight and pushes southeast through the morning
  and into the afternoon hours. While gradually weakening in the
  morning, it may re-intensify before it exists our southeast
  counties Thursday afternoon. Damaging winds will be the primary
  risk, with large hail and a few tornadoes being possible as
  well.
- Some thunderstorms may redevelop across North-Central Alabama
  Thursday late afternoon into the early evening that will have
  large hail potential, this risk will decrease in the evening as
  another MCS approaches our south-central counties from the west.

This afternoon.

The forecast area remains between a potent upper low over
Southern South Dakota and mid-level ridging over the Gulf of
Mexico, extending over the Southeast Atlantic Coast. A few areas
of lower pressure were analyzed across the Central and Northern
Plains where a cold front extended from near Omaha south to near
Tulsa then southwest extending into Southwest Texas. A warm front
extended from near Omaha east across the Ohio River Valley and
into Western New York. An outflow boundary from ongoing widespread
convection across the Northern Tennessee Valley Region extended
from Southeast Missouri into Northeast Tennessee. Surface high
pressure remains centered over the Southwest Atlantic Basin,
continuing to extend westward across much of Florida.

Isolated to scattered showers continue to move east-northeast
across much of east-central Alabama as a weak disturbance is
moving east over the area. Expect partly to mostly cloudy skies
through the afternoon with continued chances for showers and some
thunderstorm activity later this afternoon and into the early
evening with the better potential across the northern third of the
forecast area. A few storms may become strong, but organized
severe storms are not forecast this afternoon. Winds will be from
the south to southwest at 7-14 mph. High temperatures will range
from the mid 80s far north to the low 90s far south.

Tonight.

The upper low over the North-Central Plains is forecast to open
into a longwave trough this evening, with the eastern portion
becoming highly amplified as it absorbs an embedded shortwave
diving south over Minnesota. The increased upward forcing along
with favorable jet dynamics will create conditions favoring the
development of a Mesoscale Convective System (MCS) across
southeast Missouri this evening then advance southeast across the
Mid Mississippi River Valley Region and into the Tennessee Valley
Region overnight.

This activity will approach our far northwest counties just after
midnight and will continue to push southeast, affecting the
northern half of the area through the remainder of the morning
hours. The primary risk will be with damaging straight- line
winds, though large hail will be possible and we can not rule out
a tornado or two given the combination of instability and wind
shear associated with this system.

Winds will be from the southwest at 6-12 mph, the low levels will
remain well mixed to limit any potential fog development. Low
temperatures will range from the mid 60s far north to the mid 70s
southwest.

Thursday.

The MCS will continue moving southeast, affecting much of the
southern half of the area through the afternoon hours. There are
concerns for re-intensification of the MCS as it encounters a more
buoyant and unstable airmass due to daytime heating. The primary
risk will be with damaging straight-line winds, though large hail
will be possible and we can not rule out a tornado or two given
the combination of instability and wind shear associated with this
system.

There will remain chances for some redeveloping shower and
thunderstorm activity behind the MCS, most likely during the late
afternoon and into the early evening across at least the north-
central counties. Residual favorable shear profiles would support
a conditional risk for large hail in the heavier cores that manage
to develop.

This activity will give way to more widespread heavy convection
that will be approaching the southern half of the forecast area
from the west in the form of another MCS that will be pushing
across Mississippi during the afternoon and early evening hours,
which impacts to our south-central counties will be messaged in
the first portion of the long-term forecast discussion.

Through Thursday afternoon, expect winds outside of convection to
remain from the southwest at 7-14 mph. High temperatures will
range from the low 80s far east to around 90 southwest and far
south.

05

&&

.LONG TERM...
(Thursday night through next Tuesday)
Issued at 238 PM CDT WED MAY 8 2024

Conditions are shaping up for a secondary round of strong to severe
thunderstorms late Thursday night through Friday morning. This
activity will develop along the cold front which will be nearly
parallel to I-20 as a mid-level shortwave quickly moves east across
the area. The airmass will be very warm and unstable south of the
front with dewpoints in the lower to mid 70s and steep 7.5-8 C/km
lapse rates leading to large CAPE profiles (MLCAPE ~3500 J/kg).
Shear values will be amplified by the mid-level
speedmax/shortwave which will result in eff. bulk shear values
around 60 kts. This environment will foster intense convection
over the ArkLaTex and Lower MS River Valley this evening which
will rapidly grow upscale into a large MCS with damaging wind
potential maximized along embedded bowing segments as the system
moves east, generally following the instability gradient, across
the southern portions of Central Alabama early Friday morning.
There are questions regarding how far north the threat extends
given the uncertain position of the front and remnant cold pool
from the line of convection Thursday morning which could suppress
the greatest risk to the southern third of the area. Some hi-res
models indicate the potential for isolated cellular development
ahead of the MCS Thursday evening, but this is also more
uncertain. Nonetheless, anything that develops south of the cold
front will have the potential to become severe given the moist,
unstable environment. Damaging winds are by far the primary
threat, but intense updrafts may lead to large hail up to golf-
ball size in the Enhanced risk area. Straight hodographs indicate
a limited overall tornado risk outside of any microscale
interactions which could locally enhance directional shear.

The cluster of storms will begin to exit the area around 7 AM Friday
morning as the cold front continues to push south through the area,
bringing a much more pleasant airmass to the region. Humidity will
be lower on Saturday with highs in the upper 70s to lower 80s under
sunny skies. A mid-level ridge will move across the area over the
weekend as an upper-level low transitions from the Four Corners to
the Central Plains. Deep moisture returns on Monday, and models are
indicating increasing potential for another period of rainy and
stormy conditions through the early part of next week as a warm
front lifts north across the region.

86/Martin

&&

.AVIATION...
(18Z TAFS)
Issued at 1232 PM CDT WED MAY 8 2024

Scattered to broken clouds in the mid and upper levels will
persist over the area today with isolated showers through early
afternoon followed by some thunderstorm activity later this
afternoon persisting into the evening, becoming more and more
confined to the far northern portion of the area overnight, then
expanding southward through the early to mid morning hours
Thursday across the northern half of the area, then expanding
southward encompassing our south-central counties toward midday
and persisting through much of the afternoon. Thunderstorm
potential today is too limited to mention at any terminal, but
thunderstorm potential will increase through the morning and into
the afternoon hours Thursday as widespread shower and storm
activity push southeast across the area. Cloud cover will increase
tonight across the north with MVFR ceilings possible overnight,
then becoming more likely through the morning hours north and into
then through the early afternoon hours south on Thursday.

05

&&

.FIRE WEATHER...

Multiple rounds of showers and storms are expected to affect the
area beginning tonight through tomorrow. Rainfall amounts will
generally range from 1 to 2 inches. A drier airmass will return on
Friday as a cold front passes through the area with min RH of 35
to 40 percent on Saturday. 20ft winds will be out of the south-
southeast at 8 to 10 kts.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     66  86  59  77 /  70  70  40  20
Anniston    68  84  63  78 /  50  70  50  30
Birmingham  71  87  63  78 /  50  70  50  20
Tuscaloosa  72  90  64  81 /  40  60  60  20
Calera      71  86  64  80 /  40  60  60  30
Auburn      71  82  68  82 /  30  60  60  50
Montgomery  73  89  68  83 /  20  60  60  50
Troy        72  90  67  83 /  20  60  60  70

&&

.BMX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...05
LONG TERM....86/Martin
AVIATION...05