257
FXUS64 KBMX 041755
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1255 PM CDT Sat May 4 2024

...New SHORT TERM, AVIATION...

.SHORT TERM...
(This evening through Sunday)
Issued at 1233 PM CDT SAT MAY 4 2024

High pressure over the Atlantic will keep weak southerly flow
over the state with low level warm air and moisture advection
present through the short term. Today, isolated showers and
thunderstorms are possible in the afternoon across much of the
area. Instabilities will be decent, though PW values will struggle
to be at 90% for this time of year. A few storms could produce
moderate showers, but overall coverage of activity should be low.
Tonight, all activity is expected to weaken. Fog development is
likely in the areas that receive rainfall this evening. However,
visibilities and coverage will depend on the evening rainfall so
will hold off on any confidence wording for now.

Sunday, PW values are expected to increase through the afternoon
with a greater coverage of diurnal showers and thunderstorms
expected. Instabilities will be between 1500 and 2000 J/kg and
there will be a small amount of shear present. By the evening,
high res models show a feature moving into the state from the
east. with a weak mid level jet. Coverage of activity is expected
to increase through the late evening as more scattered showers and
thunderstorms move into northwest Alabama. Temperatures will be
several degrees above normal for high temperatures today and
Sunday, with low temperatures several degrees above normal
tonight.

24

&&

.LONG TERM...
(Sunday night through next Friday)
Issued at 322 AM CDT SAT MAY 4 2024

A weak southern stream shortwave currently along the Arizona/Mexico
border will trigger considerable convection along the West Texas dry
line today, eventually growing upscale into an MCS across Central
Texas. The resulting MCV/shortwave trough will reach Alabama by
Sunday evening, triggering scattered to numerous showers and storms
with PWATs near 1.75 inches, though any heavier rainfall will be
very isolated. Some of this activity may linger into Monday
morning in the northeast counties. Depending on how quickly the
shortwave exits to the east, subsidence may suppress convection
across much of Central Alabama Monday afternoon or at least keep
it isolated to widely scattered. This may warrant a decrease in
PoPs in later updates. Another shortwave moves through Monday
evening but will be much weaker as ridging builds over the eastern
CONUS, with only slight chance PoPs in the forecast.

Meanwhile a deep trough will be digging across the western CONUS and
Plains with ridging building further east. A subtropical ridge will
also be strengthening over the southwestern Gulf. Rising 500mb
heights across Central Alabama will be a limiting factor for
convection on Tuesday, though some guidance does indicate a pre-
frontal moisture axis that could trigger isolated to widely
scattered convection. Strengthening low-level southwesterly flow
will result in warming temperatures. The mid-level ridge axis pushes
east of the area Wednesday as the trough becomes positively tilted
from Ontario towards the Four Corners, but mid-levels remain warm
and fairly dry limiting convective development. Meanwhile a stalled
out front just northwest of the Ozarks may begin to advance as a
cold front Wednesday night in the wake of low pressure moving
through the Ohio Valley. One or more MCSs will probably develop off
to our northwest. Will have to keep an eye on them towards the
overnight hours given increasing bulk shear, though they may remain
just north of the area given westerly flow aloft and better height
falls remaining north of the area.

Mid-level troughing remains over the Midwest and Great Lakes
Thursday while weakening further to the west. The ridge over Central
Alabama will begin to flatten by Thursday night. A fairly strong
cold front for May will begin to move in by Thursday night. A strong
EML and associated steep mid-level lapse rates will result in a very
unstable air mass south of the front with 0-6km bulk shear values
around 50 kts. This will result in the potential for large hail and
damaging winds with any storms or MCSs that develop. Limiting
factors will be whether any leftover cold pools from Wednesday
night`s MCS(s) limit destabilization, and a tendency for better
forcing to remain north of Central Alabama. Still, will need to
monitor the potential for severe storms and heavier rainfall as
we get closer and the mesoscale details become clearer. Models
vary regarding how quickly the front clears the area Friday, but
it does look like we should see some pleasant spring weather by
next weekend after we get through summer-like conditions the next
few days.

32/Davis

&&

.AVIATION...
(18Z TAFS)
Issued at 1233 PM CDT SAT MAY 4 2024

Isolated to scattered convection is possible this afternoon. Due
to low confidence in coverage and timing of any activity over a
TAF site, have left in VCSH for now, and will amend if needed.
Tonight, activity should weaken, though there should be plenty of
low level moisture for fog development. Have included MVFR
visibilities for now, and will watch for areas of rainfall in the
evening to better determine the best coverage for fog development.

24

&&

.FIRE WEATHER...

Periods of showers and storms are forecast through Monday. Given
the scattered nature of the activity, rain amounts will average
near one-half inch, with higher amounts where thunderstorms track.
With increasing moisture, minimum RH values will be above 40
percent each afternoon. 20-foot winds should average less than 10
mph from the south to southwest, though could gust to around 25
mph and be variable in direction in or near thunderstorms.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     61  86  63  84 /  30  30  60  50
Anniston    63  86  64  85 /  30  30  60  50
Birmingham  64  88  66  85 /  20  40  60  40
Tuscaloosa  64  88  66  86 /  20  40  60  30
Calera      64  86  66  85 /  20  40  50  40
Auburn      65  85  66  84 /  30  30  40  40
Montgomery  65  88  66  87 /  20  30  40  30
Troy        64  88  65  87 /  30  30  30  30

&&

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

$$

SHORT TERM...24
LONG TERM....32
AVIATION...24