949
FXUS64 KBMX 081126
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
626 AM CDT Wed May 8 2024

...New AVIATION...

.SHORT TERM...
(Today through Thursday)
Issued at 355 AM CDT WED MAY 8 2024

Key message:

- Multiple rounds of strong to severe storms are possible tonight
  through Thursday night with damaging winds and large hail
  possible. Timing and location of the highest threat areas remain
  uncertain.

Today through Midnight:

For today, we will be in a preparation state across the area
before the first of several waves of showers and storms move into
the area. By the afternoon, isolated to scattered showers and a
few storms will be possible. A few stronger storms will certainly
be possible as the area will be a tad more stable that the south.
Areas in the south will reach the low 90s by the afternoon, so any
shower/storm that develops down here certainly will be strong.
Most activity will dissipate after sunset, albeit briefly. At this
time there does not appear to be organized severe weather threat
through the early evening hours tonight.

16

After midnight tonight through Thursday afternoon:

The rex block over the western CONUS and Plains will be
transitioning to an omega block over the eastern Pacific and
western CONUS tonight. As this occurs the upper low over South
Dakota/Nebraska will break into three piece. The western piece
will become an upper low forming near the Grand Canyon, the middle
piece will become a shortwave that eventually dives southward
across the Mid South Thursday night, and the eastern piece will
get absorbed into a northern stream trough over the Great Lakes.
Meanwhile a strong subtropical ridge will be centered over the Bay
of Campeche. At the surface a somewhat disorganized but
sub-1000mb low pressure area will move eastward from Missouri to
the Ohio Valley. A trailing cold front will move only slowly
southeastward, finally reaching Central Alabama Thursday night,
while a warm and humid air mass will be present ahead of it.

Convection developing over the Mid-South will grow upscale into an
MCS tonight aided by a 35kt LLJ which has trended weaker with
recent runs. Convection along the trailing outflow from this MCS
will eventually sink southward into our northern counties late
tonight, with the arrival time trending later. Any isolated cells
that are able to develop ahead of this line this evening would be
potentially capable of all modes of severe weather, though
increased capping/warming 700mb temps make this a low probability
chance at this time. The MCS should be weakening as it moves into
our northern counties late tonight/early tomorrow morning as the
LLJ veers/weakens and shear vectors become parallel to the outflow
boundary. However, the unusually warm and moist air mass and
steep mid-level lapse rates will keep CAPE values above 1000 J/kg,
so it may still be capable of producing severe weather.

Of more concern is the slower trend with the progression of the
outflow boundary, with the potential for the MCS to re-intensify
or a new MCS to develop as daytime heating occurs ahead of the
outflow boundary, potentially aided by a subtle shortwave in the
morning. CAPE values increasing to 2000-3000 J/kg by late morning,
0-6 km bulk shear around 50 kts, and plenty of dry air
aloft/DCAPE would become very favorable for damaging winds mainly
along and east of I-65 if this occurs, before the MCS pushes into
Georgia. Therefore the severe risk has been upgraded to a Level 2
out of 5 slight risk. (Note: we`ve combined the late tonight risk
and the tomorrow daytime risk on one threat graphic; an
additional threat graphic covers the potential next wave tomorrow
night). While this scenario is starting to become more plausible,
and could warrant a further increase in severe risk, it`s also
plausible that the line could push into Georgia before
strengthening too much. Will have to keep watching model trends as
this will be heavily dependent on mesoscale lifting by the
outflow boundary as the only source of forcing. Any individual
cells that can develop would also become capable of producing hail
given the steep lapse rates, potentially larger than quarter
size. It still looks like there will be some subsidence developing
by afternoon with weakly anticyclonic flow and some drying aloft,
to the west of the MCS. Though, some isolated severe storms may
still be possible during this time, ahead of another potential
round of severe storms discussed below in the long term section.

32/Davis

&&

.LONG TERM...
(Thursday night through next Tuesday)
Issued at 355 AM CDT WED MAY 8 2024

A subtle mid-level speed max/southern stream shortwave is expected
to help initiate convection ahead of the front over the ArkLaTex
Thursday afternoon. As this feature moves eastward, it`s unclear
if these storms will grow upscale into an MCS or if there will
just be various clusters of storms. With a very unstable air mass
and steep mid-level lapse rates of 7.5 to 8 C/km persisting south
of the front, as well as strong bulk shear, the severe threat is
expected to persist or re-develop Thursday evening through the
overnight hours. In addition, a shortwave digging across the Mid-
South will result in height falls across the area. Will indicate
a Level 2 out of 5 slight risk focused across the southern half of
the area for a continued threat of damaging winds as well as
large hail with any supercells. Low-level shear appears too weak
for a threat of tornadoes at this time.

The cold front will push through the area Friday morning,
providing welcome relief from the heat and storms. The upper low
over the southwest CONUS will eventually move eastward early next
week. Models have trended a bit quicker and wetter with this
system

32/Davis

&&

.AVIATION...
(12Z TAFS)
Issued at 622 AM CDT WED MAY 8 2024

MVFR ceilings have developed at all sites. There could be a brief
drop to IFR at spots, but the predominate will be MVFR. The
ceilings will slowly rise and become VFR by 16-18z. Showers and
thunderstorms are possible again this afternoon and have the
northern sites in a VCSH for the afternoon hours then clearing out
after 21 to 23z. Winds will become 5-10 kts during the day and
then remain that way through the night. MVFR clouds will redevelop
after 6z with showers and storms moving in from the north.

16

&&

.FIRE WEATHER...

Isolated to scattered showers and storms are possible this
afternoon with greater rain chances overnight and Thursday.
Rainfall amounts will average 0.5-1.0 inch under heavier storms.
Afternoon minimum RH values will be above 45-50 percent this
afternoon and then higher on Thursday. 20-foot winds will be
8-12 mph this afternoon and Thursday. Wind gusts to around 25
to 30 mph are possible near convection. Most of the rain will end
by Friday afternoon, with a dry forecast through the weekend and
first of next week.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     88  67  86  61 /  30  70  90  40
Anniston    88  69  85  64 /  30  50  90  50
Birmingham  88  70  86  63 /  30  50  90  50
Tuscaloosa  89  71  88  65 /  30  50  80  50
Calera      88  71  86  64 /  30  50  90  60
Auburn      87  72  85  67 /  20  20  80  60
Montgomery  91  72  89  67 /  30  20  80  60
Troy        91  72  89  68 /  20  10  70  60

&&

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

$$

SHORT TERM...16/32
LONG TERM....32
AVIATION...16