327
FXUS64 KBMX 250542
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1242 AM CDT Wed Sep 25 2024

...New AVIATION...

.SHORT TERM...
(Tonight through Thursday)
Issued at 848 PM CDT TUE SEP 24 2024

The cold front is back over northern Mississippi, but a pre-
frontal trough/outflow boundary is currently serving as a focus
for showers and storms over our northwest counties. This boundary
and band of showers and storms will make only slow southeastward
progress tonight. An upper low is in the progress of closing off
over Missouri while a seasonally deep trough digs into the Lower
Mississippi Valley. Forcing associated with this trough and the
right entrance region of an upper-level jet streak will maintain
showers and storms overnight in this vicinity, with more scattered
activity further east in the southerly flow. With some potential
for training some locally heavy rainfall is possible overnight
across portions of West Alabama with minor flooding possible as
well as a low but non-zero chance for flash flooding.

Tomorrow the focus for showers and storms will shift to East
Alabama by afternoon where some heating will occur east of the
boundary and tropical moisture increases ahead of Helene. Upper
forcing associated with the trough will continue as well. With
some heating in the southeast counties, CAPE values increase above
1000 J/kg with 35-45 kts of shear capable of producing some
supercells and bowing segments. Low-level shear and SRH are very
weak, so any tornado threat appears extremely low, but isolated
damaging winds and some hail will be possible with cooling temps
aloft. Will be watching the new runs coming in this evening to
determine if a flood watch will be needed starting Wednesday
afternoon and Wednesday night for some of the eastern counties,
ahead of the more significant heavy rains coming in Thursday with
Helene.

32/JDavis

Previous short-term discussion:
(This evening through Wednesday)
Issued at 1220 PM CDT TUE SEP 24 2024

A boundary will continue to move southeast towards northwest
Alabama this afternoon and evening. Ahead of this boundary,
isolated showers and thunderstorms are possible, mainly in areas
of I85 and north. The boundary is expected to move into the
northwestern counties this evening, after sunset, and linger over
the northwestern third of the state through much of the night.
This boundary will provide plenty of lift for showers and isolated
thunderstorms to continue through the night across the
northwestern half of the state, increasing in coverage and
intensity as the boundary moves to the southeast Wednesday. PW
values will slowly be increasing through the day today, with
values around 90% to max by Tuesday evening.

Wednesday, as the boundary slowly moves to the southeast through
the day, winds ahead of the boundary will be from the southwest,
while northerly weak winds will be behind the boundary. Moisture
will be high in southeast areas where the southwest flow is more
consistent. Instability will also be stronger in these areas, with
values around 2000-2500 J/kg possible from the late morning
through the afternoon. Models are showing an area of higher low
and mid level winds in this same area, with plenty of speed and
wind shear. CAMs show scattered development across the southeast
beginning around mid morning, and lasting through the rest of the
day. With all this said, there is potential for strong to severe
storms in the southeast, along counties just north of I85 and
south. The coverage and chance for severe depends on how much
convection develops across the coast. If convection becomes more
widespread along the coast, the severe potential will be limited,
but if the scattered activity can develop first, there is a chance
for damaging winds and storms to rotate. Will have to keep an eye
on updates to see where the greatest shear and instability will
be, as well as how much convection is expected to develop.

The rest of the area could continue to see scattered convection,
though with little to no severe threat as the instability will be
much lower. This will continue through the late afternoon and
early evening as the front weakens. With so much convection
expected through the night and Wednesday, as well as the northerly
flow north of the boundary, high temperatures on Wednesday will be
in the mid 70s to lower 80s, a good 10 degrees cooler than
Tuesdays highs in the upper 80s to lower 90s.

24

&&

.LONG TERM...
(Wednesday night through next Monday)
Issued at 200 PM CDT TUE SEP 24 2024

Current forecast and impacts from Tropical Storm Helene remain on
track this afternoon. The convergent area noted in the previous
discussion will provide the focus for heavy rainfall, most of
which will occur Thursday and Thursday night, across the eastern
half of the forecast area. Rainfall totals east of I-65 of 3-7
inches are possible.

The current track keeps the strongest winds east of the forecast
area, but given the quick forward speed, cannot completely rule
out tropical storm force winds in the southeastern and eastern
portions of the area Thursday night.

14

Previous long-term discussion:
(Wednesday night through next Monday)
Issued at 342 AM CDT TUE SEP 24 2024

The main focus for the extended period is the potential tropical
cyclone in the Gulf of Mexico.

Guidance has been consistent in showing the larger-scale upper
trough developing into a cutoff low over the Mid-MS Valley Wednesday
night into early Thursday. As this takes place, the potential
tropical cyclone is forecast to be intensifying prior to landfall in
Florida. The tropical system is then expected to interact with the
cut-off upper low and we start to see the Fujiwara effect take
place with the tropical system and cut-off low rotating around
each other before the tropical low becomes absorbed in the broader
trough sometime Friday night into Saturday.

Impacts:

Flooding: Two separate features will lead to at least 2 distinct
areas of flooding potential. First, the stalled frontal
boundary/moisture convergence discussed in the short term. Then, the
banding on the northwest side of the tropical track that could set
up in the eastern and southeastern portions of Central AL Thursday.
The placement of this axis of heavy rain will greatly depend on the
eventual track, so updates on this area will be needed in coming
days.

Wind: Winds will steadily increase through the day on Thursday as
the system gets closer. The forward speed of this tropical system is
a big concern as the stronger winds will tend to translate further
inland with a faster-moving storm. Current forecasts have maximum
wind gusts generally in the 30-40mph range for the eastern half of
Central AL, and gusts of 20-30 in the western half. This could
change depending on the eventual track and intensity.

This is a quick-moving system and by Friday morning/early afternoon,
the potential tropical cyclone has largely merged in with the the
upper level low. We`ll still see some lingering rainfall on the
backside of the low through Friday evening, but that diminishes
by Friday night/Saturday morning, leaving lower rain chances
across the area for the weekend.

25/Owen

&&

.AVIATION...
(06Z TAFS)
Issued at 1230 AM CDT WED SEP 25 2024

A slow-moving pre-frontal trough will continue to move slowly
southeastward through the night. Along the line showers and a few
thunderstorms will continue to develop. These will cause
occasional visibility drops at times. Highest rain probabilities
will be across TCL/BHM/EET/ANB/ASN through the morning, shifting
to MGM/ANB by the afternoon. MVFR cigs are also expected to
develop late morning and may temporarily drop to IFR. Winds will
be light through the morning, becoming northeasterly to easterly
at 4 to 7 kts after 15z.

16

&&

.FIRE WEATHER...

Increasing rain chances expected today through Thursday as a frontal
boundary moves into the region and stalls. Tropical moisture
builds into the area ahead of the potential tropical cyclone
Wednesday through Friday keeping Min RHs 60-70%+. Winds increase
substantially on Thursday as the tropical system approaches. Gusts
could exceed 30mph in the eastern half of Central AL.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     78  66  73  62 /  80  70  90  80
Anniston    78  67  75  65 /  80  80 100  80
Birmingham  78  66  74  64 /  80  60  80  70
Tuscaloosa  78  65  78  65 /  80  40  60  50
Calera      79  67  76  67 /  70  60  80  70
Auburn      80  70  76  67 /  90  90 100  80
Montgomery  84  70  76  67 /  90  90  90  70
Troy        82  70  74  65 /  90  90 100  70

&&

.BMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch from this afternoon through Friday morning for the
following counties: Barbour-Bullock-Chambers-Cherokee-Clay-
Cleburne-Lee-Macon-Pike-Randolph-Russell-Tallapoosa.

&&

$$

SHORT TERM...32
LONG TERM....14
AVIATION...16