-- Discussion containing changed information from previous version are highlighted. --
276
FXUS64 KBMX 231901
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
201 PM CDT Mon Sep 23 2024

...New LONG TERM...

.SHORT TERM...
(This afternoon through Tuesday)
Issued at 1151 AM CDT MON SEP 23 2024

High pressure over the southeast will slowly move eastward through the day,
with low and mid level winds transitioning to out of the southwest by
tonight. This afternoon, there is just enough instability,
roughly between 2000 and 2500 J/kg for isolated showers and a
thunderstorm to develop, though forcing and moisture will be
weak. Left in a slight chance for activity this afternoon,
weakening around sunset. Overnight through Tuesday, a low pressure
system moves through the Ohio Valley with a frontal boundary
approaching from the northwest. CAMs are fairly consistent that
the boundary should slowly slide into the northwestern counties in
central AL by the evening, lingering over the north and west
parts of the area into the overnight hours. Moisture is expected
to increase from the 50th percentile today to the 90th percentile
by Tuesday afternoon. There will be plenty of moisture, lift, and
shear, though instability will be low as the front moves in.
Scattered showers and thunderstorms are likely to develop along
this boundary, with activity moving southwest to northeast, with
training storms possible.

24

&&

.LONG TERM...
-- Changed Discussion --
(Tuesday night through next Sunday)
Issued at 142 PM CDT MON SEP 23 2024

Adjustments were needed this afternoon to pops and qpf, given the
latest model trends regarding the upper cutoff low and potential
tropical disturbance. Rain chances have increased for Wednesday as
the upper low approaches from the northwest with moisture
advecting northward ahead of the tropical disturbance. A
convergent zone over the area will lead to widespread rain and a
few storms. Additional rainfall and windy conditions are expected
Thursday, with the influence of the tropical disturbance moving
northward from the Gulf. Exact impacts will depend on track and
strength as that system moves inland. Currently, rainfall totals
Wed through Fri range from near 2 inches in the southwest to 5
inches along the Georgia state line.

14

Previous long-term discussion:
(Tuesday night through Sunday)
Issued at 354 AM CDT MON SEP 23 2024

All eyes should be fixated on the Gulf of Mexico by midweek as we
watch a developing tropical cyclone. Operational models and
ensemble members are strongly indicating the potential for a
large tropical cyclone to move quickly from the Yucatan Channel
toward the Florida Panhandle. *For official tropical cyclone
forecasts, please refer to information from the National Hurricane
Center*

An upper-level trough is expected to move southward and become cut
off over Arkansas on Wednesday. An associated weak front will
move into northwestern Alabama bringing a potential for showers
and storms Tuesday night. The tropical cyclone is expected to
begin interacting with the mid-latitude trough and front on
Wednesday, with a developing inverted surface trough over Alabama.
Therefore, we will begin feeling the effects of the Gulf system
on Wednesday, with the potential for a nearly stationary corridor
of rain.

A highly unusual scenario is expected to play out as the tropical
cyclone moves toward the northern Gulf of Mexico. I do not recall
ever seeing the Fujiwara effect take place in this part of the
country, but that is indeed what nearly all models are indicating.
As the tropical cyclone becomes captured by the cut-off mid-
latitude trough, it appears the tropical cyclone will rapidly
accelerate northward while the cutoff moves southwestward. With
the two cyclones so close in proximity, these cyclones will rotate
around each other before merging into a larger gyre after the
tropical cyclone makes landfall Thursday or early Friday. The
exact track of the tropical cyclone is not pinned down, but there
is a potential for the center of this system to move into Alabama
or close enough to produce impacts from heavy rain and high winds
Thursday and early Friday. If the modeled forward speed of 20-25
knots is correct, the tropical cyclone will have little time to
weaken before reaching areas well inland.

As the systems merge to form a larger cut-off trough to our
northwest, a dry slot is expected to reduce our rain chances for
Friday afternoon through the weekend.

87/Grantham
-- End Changed Discussion --

&&

.AVIATION...
(18Z TAFS)
Issued at 1151 AM CDT MON SEP 23 2024

Isolated showers and thunderstorms are possible this afternoon,
mainly across the northern half of the area. Left mention of VCSH
out of each TAF for now due to uncertainty in timing and coverage.
Activity should weaken after sunset with scattered convection
developing early Tuesday afternoon, at the end of the current TAF
period.

24

&&

.FIRE WEATHER...

-- Changed Discussion --
Isolated showers or storms are possible Tuesday afternoon across
the north and west, but expect most of the area to remain dry.
With temperatures in the 90s and a modestly dry airmass in place,
minimum RH values should range from 35 to 55 percent again Tuesday.
20 foot winds will be southwesterly at less than 7 mph through
Tuesday. A significant increase in moisture and rain chances is
expected on Wednesday and Thursday as a potential tropical system
moves toward the northern Gulf of Mexico.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
Gadsden     68  91  65  80 /   0  20  60  80
Anniston    70  90  68  81 /   0  10  50  80
Birmingham  72  91  68  81 /   0  20  60  80
Tuscaloosa  71  91  68  82 /   0  20  60  80
Calera      73  91  70  82 /   0  10  50  80
Auburn      71  91  70  83 /   0  10  30  70
Montgomery  72  94  71  84 /   0  10  30  80
Troy        70  91  69  82 /   0  10  30  70
-- End Changed Discussion --

&&

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

$$

SHORT TERM...24
LONG TERM....14
AVIATION...24