694
FXUS64 KBMX 240015
AFDBMX

Area Forecast Discussion National Weather Service Birmingham AL 714
PM CDT Mon Sep 23 2024

...New AVIATION...

.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...
(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

&&

.AVIATION...
(00Z TAFS) Issued at 710 PM CDT MON SEP 23 2024

VFR TAF forecast is expected for the next 24 hours. Any isolated
showers out there will be quickly deteriorating over the next hour
or so with some mid level lingering clouds left behind. Winds will
be light/variable to near calm tonight. Winds during the afternoon
on Tue will be generally SW ~5-7kts except for MGM which may be more
SRLY. Shower activity will approach from the NW on Tue ahead of a
front but should generally remain NW of NRN TAF sites. Pops will be
too low to mention in TAFs at this time.

08

&&

.FIRE WEATHER...

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.

&&

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

&&

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

$$

SHORT TERM...24
LONG TERM....14/87/Grantham
AVIATION...08