616
FXUS64 KBMX 091202
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
702 AM CDT Thu May 9 2024

...New AVIATION...

.MESOSCALE UPDATE FOR SEVERE WEATHER THROUGH LATE MORNING...
Issued at 418 AM CDT THU MAY 9 2024

A Mesoscale Convective System was moving southeast across
Northern Mississippi and much of Southern Tennessee. The overall
storm motion was southeast around 30 mph with a quick storm track
projecting arrival times near 6:30 am for Gadsden, 7:00 am for
Birmingham and 7:30 am for the Anniston metro areas. Further west,
the arrival times for activity is more uncertain as activity is
moving more eastward over the Mid-South Region.

Locally, showers have rapidly developed over the past 30 minutes,
likely in response to the arrival of 100 kt winds at 200 mb
progged by the RAP 13 km model currently. This activity is
expected to continue to develop and move east-northeast in the
established low-level flow from the southwest in the 700 mb - 925
mb layer. A defined shortwave trough at 500 mb was analyzed by
mesoscale modeling over North-Central Louisiana and is progged to
move northeast over the area later this morning, further
supporting additional convective activity.

The environment is very supportive of continued convective
activity as the 09/00z BMX sounding from last night contained
nearly 3500 J/kg of SBCAPE that fed the intense storms over the
Tennessee Valley Region. Mesoscale data suggests current
instability values are a bit lower, typical for this time of day
with the forecast low temperatures occurring, with values from
1600-2000 across the west and northwest portions of the area while
lower instability values found across the far east/southeast. 0-6
km Bulk Shear values range from around 40 kts over North Alabama
to near 50 kts over the southern portion of the area. These values
are sufficient to support storm organization and persistence, of
which already a few heavier showers ahead of the heavy convection
moving southeast are exhibiting deviant storm motions with a storm
split that recently occurred over Northeast Marshall County.

Through late morning, we will be monitoring the progress of the
MCS as it continues to move generally southeast into the forecast
area. We will be closely watching shower activity that is
expected to continue to develop and move northeast. This activity
will have the potential to further develop into thunderstorms as
it traverses the unstable and sufficiently sheared environment.
Discrete mature convection ahead of the MCS will have the best
potential of producing tornado activity along with damaging winds
being a secondary risk. The MCS itself will have the best
potential for producing damaging winds, though an embedded tornado
or two will remain possible.

05

&&

.SHORT TERM...
(Today through Friday)
Issued at 115 AM CDT THU MAY 9 2024

Key Messages:

- A Mesoscale Convective System dives southeast into the area
  before sunrise and push 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 late
  morning into the 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
  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.

- The second MCS appears to track a touch to the north of the
  previous forecast, so the severe chances have increased across
  the southern areas. Damaging winds will be the primary
  risk, with large hail and a few tornadoes being possible as
  well.

We will be watching a MCS that is currently across western TN.
This MCS should dive southeast into the area before sunrise and
push 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 late morning into the
afternoon. There may be a line of showers and storms that develops
as well and will merge with this first area. Highest confidence
right now would be with the MCS to or northwest moving down and
then spreading out. Damaging winds will be the primary risk, with
large hail and a few tornadoes being possible as well, especially
if there is a merge of lines. There will be a brief lull before
the next system moves in.

Conditions are shaping up for a secondary round of strong to
severe thunderstorms late tonight through Friday morning. This
activity will likely 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 still 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 to our west which will rapidly grow into a large MCS
with damaging wind potential maximized along embedded bowing
segments as the system moves east, 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 this morning/afternoon which could suppress the
greatest risk to the southern third of the area. 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 in the Enhanced risk area.

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.

&&

.LONG TERM...
(Friday night through next Wednesday)
Issued at 245 AM CDT THU MAY 9 2024

Dry conditions return Friday night as the system exits to our
east. 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, with an 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.

16

&&

.AVIATION...
(12Z TAFS)
Issued at 702 AM CDT THU MAY 9 2024

Almost all sites have already dropped to MVFR ahead of the next
round of showers/storms. We may briefly see sites drop to IFR
before the band gets in, especially at TOI. The biggest impact
should be the storms as they move into the northern TAF sites
within the next hour or two. This round will slide south of the
northern sites by 16 to 18z and out of the southern sites by 19
to 21z. Conditions will improve to VFR for most of the rest of
the cycle, but begin to decrease at TCL by 3z ahead of the next
round of showers and storms along a cold front. Looks like the
main impact here will be between 6 and 12z.

16

&&

.FIRE WEATHER...

Multiple rounds of showers and storms are expected to affect the
area through Friday morning. 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     86  61  78  49 / 100  30  20   0
Anniston    85  64  79  52 / 100  50  30   0
Birmingham  86  64  79  54 / 100  50  20   0
Tuscaloosa  87  66  81  55 / 100  60  20   0
Calera      85  66  80  55 / 100  60  30   0
Auburn      82  69  81  57 /  90  80  50   0
Montgomery  86  69  84  57 /  90  80  50   0
Troy        86  68  83  57 /  90  80  60   0

&&

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

$$

SHORT TERM...05
LONG TERM....16
AVIATION...16