348
FXUS64 KBMX 111144
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
644 AM CDT Wed Sep 11 2024

...New AVIATION...

.SHORT TERM...
(Today through Friday)
Issued at 350 AM CDT WED SEP 11 2024

Francine is forecast to move toward the Louisiana coast later today,
then move inland through the lower Mississippi Valley into Thursday
morning per latest NHC forecasts. Until then, PoPs and other weather
elements have not changed much. Most of our area is under influence
by drier air wedged through the southern Appalachians where PWs well
below 1" reside in an easterly low-level flow. However, continued
isentropic ascent will occur today, and virga currently evident on
88D data will slowly become light to moderate stratiform rain or
showers throughout the day as the mid- to low-levels saturate. More
substantial increases in PoPs and winds will occur after Midnight
tonight, as Francine`s circulation moves into southern Mississippi.

Recent trends in the forecast path for Francine have shifted
eastward. As such, our overall forecast impacts, combined with
better clarity from hi-res guidance, have increased. These are
summarized below:

* Flooding: Locally heavy rainfall is possible tonight through
  Thursday night, especially with any north-to-south oriented
  convective bands that form. There`s some indication in CAM
  guidance of this occurring during the peak overlap of MUCAPE,
  PWs, and low-level convergence Thursday morning through Thursday
  night, and there`s been support in global models for this as
  well. Any slow-moving band of convection would pose a threat for
  flash flooding, mainly urban or poor-drainage areas. Otherwise,
  unfavorable hydrologic conditions (due to ongoing drought)
  should tend to inhibit any major problems in rural areas. It`s
  also possible that the influx of deep-layer shear will keep
  convection more discrete in nature, which could lead to other
  issues. Due to the conditional nature of the flooding threat, a
  Flood Watch is not being issued at this time.

* Tornado: Low-level kinematics surrounding the eastern portion of
  Francine`s circulation will support modest hodograph curvature
  characterized by 200-400 m2/s2 0-3 km SRH. These values have an
  overlap with the depicted axis of instability on the latest
  HREF, generally 500-1,000 J/kg SBCAPE. (Extreme values of SRH
  you may see on prognostic charts are actually north of the warm
  front/advancing warm sector.) Thus, latest CAMs/HREF seem to be
  showing better clarity on a potential tornado threat, and this
  would generally be the same convective activity that could pose
  our flooding threat. Timing is mainly Thursday morning through
  Thursday night, and all of Central Alabama is under some level
  of risk. Please refer to our latest graphics for those details
  as they will be updated more frequently from this point.

* Wind: Gusts up to ~40 mph are forecast on Thursday. These windy
  conditions are expected across the western 2/3, or so, of Central
  Alabama. A Wind Advisory will be needed soon, and this is the most
  likely product scenario given the forecast extratropical
  transition that occurs during this time frame.

Francine is forecast to continue generally northward toward the mid
Mississippi Valley late Thursday into early Friday morning. A dry
slot is progged to advance across Alabama from the west, bifurcating
the tropical moisture to our northwest and southeast, and the low-
level jet will lift to our north. PoPs make a noticeable decrease
from the west as a result, though lingering activity from residual
tropical moisture and the meandering remnant low will have some
impact discussed in the long-term.

40/Sizemore

&&

.LONG TERM...
(Friday through next Tuesday)
Issued at 350 AM CDT WED SEP 11 2024

As most guidance suggests, Francine will make an extratropical
transition as it continues north toward the mid Mississippi Valley
on Friday, occluding thereafter and potentially stalling as it
encounters resistance from a ridge near the Great Lakes region. We
should have already seen a dry slot move across the area from the
west during this time, and this will move best rain chances east of
I-65. With the remnant low pressure system in the region, and
lingering moisture throughout the boundary layer, we`ll likely see
isolated to scattered diurnal convection through at least Monday.
Tuesday has the potential of being dry with the consensus of the
models transferring much of the energy to system along the Atlantic
coast by then, but will hold onto some slight chance PoPs with the
moisture still in place across the area.  High temperatures will
generally be in the 80s each afternoon outside of some cooler spots
in the northeast counties.

16

&&

.AVIATION...
(12Z TAFS)
Issued at 640 AM CDT WED SEP 11 2024

Considerable cloudiness, mainly cirrus, continues across Central
Alabama. We are beginning to see some of the clouds drop in the
south to around 5000 feet, but MVFR remains to the south of the
area. Looks like we may drop to MVFR for the afternoon with
advancement of some light rain. The northern sites will see a
chance of MVFR ceilings generally in the late afternoon/evening
with rain that may move into the TCL/EET and BHM sites as
Hurricane Francine arrives near the Louisiana coast. Better rain
chances will move in after 00z. Winds will remain east to
southeast, increasing to 10 to 20 kts after 15z.

NOTE: NIL TAF continues for KANB until further notice due to large
comms issue and missing obs.

16

&&

.FIRE WEATHER...

Rain chances continue to increase through tonight with the arrival
of tropical moisture. Rainfall becomes widespread into Thursday
along with the chance for some severe weather along with flooding.
Minimum relative humidity values will increase as overall moisture
increases. 20 foot winds are forecast to be 10 to 15 mph today and
higher on Thursday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     84  65  74  67 /  10  60  80  90
Anniston    83  67  76  68 /  20  70  90  90
Birmingham  83  67  75  69 /  30  70  90  90
Tuscaloosa  82  68  78  68 /  50  90 100  60
Calera      81  68  77  69 /  40  80 100  90
Auburn      79  67  76  69 /  50  70  90  90
Montgomery  78  69  80  71 /  70  80  90  60
Troy        76  68  79  70 /  70  80  90  60

&&

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

$$

SHORT TERM...40
LONG TERM....16
AVIATION...16