774
FXUS64 KMOB 100018
AFDMOB

Area Forecast Discussion
National Weather Service Mobile AL
718 PM CDT Thu May 9 2024

...New MESOSCALE UPDATE...

.MESOSCALE UPDATE...

Issued at 718 PM CDT Thu May 09 2024

Convective evolution as we go through the rest of the evening into
the overnight hours remains very complex with a higher degree of
uncertainty than normal.

Severe thunderstorms have quickly developed across central Alabama
and west central Mississippi early this evening in advance of a
shortwave currently moving across MS. Very subtle height falls have
occurred ahead of this wave up in that region, which has been enough
to overcome a small cap around 750mb (as observed on the 00z JAN
sounding). Storms have also focused up in that region along a subtle
west to east oriented boundary. Meanwhile, further south in our
area, the influence of this wave has not been enough to overcome
this aforementioned cap up until this point. A few storms are trying
to develop in south central AL from Crenshaw County eastward along a
residual outflow boundary, but so far the capping has won out. As we
go through the night, subtle height falls will spreads into the area
from the west ahead of a stronger shortwaves that has resulted in
the deep convection across east TX.

While the specific evolution of the convection is uncertain, we
expect a gradual increase in convective coverage across the far
northern portions of the forecast area by late evening, potentially
influenced by a southward moving outflow boundary generated by cold
pools from the central AL convection. Also, convective coverage will
likely quickly increase back to our west across LA/MS late tonight
with the influence of the aforementioned shortwave. This convection
will spread east into the area overnight (mainly after midnight) and
will impact at least the northern half to two-thirds of the forecast
area. How far south this convection makes it is still uncertain.

The airmass ahead of this convection could not be any more favorable
for severe weather. SBCAPES range from 3000 to 5000 j/kg as of
00z, with the highest values in the western half of the area.
Similar values will persist through the night. In addition, model
guidance has been emphatic on spreading in an elevated mixed layer
with mid level lapse rates near or in the excess of 8 C/km. This
was confirmed in the JAN sounding which showed 8.5 C/km. In
addition, deep layer shear on the order of 50-60 kt will be very
supportive of severe weather. Much of this shear is in the mid to
upper levels with weaker flow in the low levels. This favors very
strong cold pools that will drive a damaging wind threat and
perhaps a significant wind event numerous gusts over 70mph
possible. The damaging wind threat will increase with time as
clusters of storms organize and it is possible we will have to
contend with a west to east moving MCS across the area overnight.
If an MCS does organize, there could be some swaths of significant
wind damage along with the possibility of a few tornadoes. Prior
to the potential organization of a storm complex, individual
supercells that develop will carry a substantial large hail threat
as straight line hodographs favor splitting supercells, with the
left movers being the more likely sig hail producers.

The greatest severe threat will likely shift east of the area by 5-
6am. How all the convection evolves overnight will determine what
the extent of the threat will be closer to the coast in the predawn
to morning hours on Friday. There will certainly be a severe threat
in this area, but how much will hinge on how far south the
initial convection makes it and if there is a lingering boundary
to focus convection along the I-10 corridor through Friday morning.
34/JFB

&&

.PREV DISCUSSION... /issued 701 PM CDT Thu May 9 2024/

..New AVIATION...

UPDATE...
Issued at 701 PM CDT Thu May 9 2024

We are continuing to monitor trends for potential severe
weather later tonight, and an updated Mesoscale discussion will
be issued shortly.

AVIATION...
(00Z TAFS)
Issued at 701 PM CDT Thu May 9 2024

General VFR conditions with local mid MVFR ceilings and isolated
to scattered rain showers and thunderstorms are expected early
this evening. We still expect that conditions will likely
deteriorate later tonight into early Friday morning as several
rounds of convection move east across the area. A cold front will
sag south across the area through Friday morning, bringing low end
MVFR/IFR conditions and more widespread showers and storms. Some
of the storms could be intense, with strong damaging winds and
large hail. South to southwesterly winds of 10 to 15 knots through
late tonight, but with locally variable strong winds near the
convection. Winds shift to more westerly late tonight and then
northwesterly Friday morning as the front passes and convection
ends. VFR conditions expected by afternoon. DS/12

PREV DISCUSSION... /issued 353 PM CDT Thu May 9 2024/

.New NEAR TERM, SHORT TERM, LONG TERM, MARINE...

NEAR TERM...
(Now through Friday)
Issued at 350 PM CDT Thu May 9 2024

A very complicated and active
pattern will evolve over the next 24 hours bringing potentially a
couple rounds of sever storms to the area. This afternoon, the
atmosphere has become very unstable with around 3000J/kg of MLCAPE
due to temps around 90 an dewpoints in the mid 70s. Meanwhile we are
monitoring for development along the remnant outflow/sfc cold front
sagging southward into central Alabama. At this time, most of the
development has been east of the area due to the lack of forcing and
a capping warm layer aloft. However as the outflow boundary moves
south, storm development is possible through this evening mainly
across northeastern portions of the area and with strong instability
and favorable deep layer shear, storms would likely become severe
with large hail and damaging winds. The main show is expected to
come overnight tonight as the next shortwave approaches. Storms are
expected to develop this evening over the Arklatex region and
quickly evolve into a thunderstorm complex(MCS) and move east. The
MCS is expected to quickly move east driven by a strong cold pool.
Instability values remain high due steep mid level lapse rates
around 8c/km. This MCS is expected to ride the remnant outflow
boundary some near the highway 84 corridor. Given the environment in
place, damaging to potentially destructive winds of 60 to 80+ mph
will likely swiftly move across interior areas of our area. A couple
tornadoes cannot be ruled out; however, low level shear might be a
little too weak to really get the QLCS tornadoes going.

A final very conditional round of strong to severe storms is
possible Friday morning. This round is very low confidence and more
marginal. It is highly dependent on the overnight storms and if
storms are able to develop in the wake of the overnight MCS. These
storms would likely be somewhat elevated above the left over cold
pool, so large hail would be the main threat. While heavy rain will
be possible, the duration is expected to remain short enough to
prevent more than just localized minor flooding.

Coastal Hazards...With moderate southerly flow persisting through
the period, a HIGH risk of rip currents will be possible through
Friday. /13

SHORT THROUGH EXTENDED TERM...
(Friday night through Thursday)
Issued at 350 PM CDT Thu May 9 2024

As the upper level shortwave trough over the Southeast Friday evening
moves off, an upper ridge over the Southern Plains shifts east over
the Southeast ahead of a eastward moving closed low over the Desert
Southwest. Guidance is advertising several rounds of shortwave
energy moving over the Southeast beginning Sunday night and lasting
into Tuesday before the positively tilted upper low passes north of
the forecast area. The cold front which stalled over the Gulf of
Mexico moves north as a warm front over the Southeast Monday into
Tuesday, drawn north with a closed surface low moving north along
the Mississippi River. This will bring a first round of
precipitation to the forecast area. There is a chance of strong to
severe storms Monday into early Tuesday which will be addressed
below. Tuesday night on, guidance has been inconsistent with the
strength of the cold front and moisture levels behind, resulting in
variations with PoPs Wednesday and after. Have tried to even out the
variations, remaining close to the NBM for this issuance.

Taking a closer look at weather for Monday into Tuesday and severe
storms, south of the warm front, guidance is advertising SBCapes
rising into the 2000-2500J/kg range. Add in good wind shear (Bulk
wind shear topping out between 50 and 60kts Monday night into
Tuesday), and an increased risk of severe weather returning to the
forecast area. There is some disagreement in the guidance in how far
inland the warm front will go, so painting an area is hard to pin
down at this time. In addition to possible strong to severe storms,
will need to monitor for water issues, with the good overrunning of
the warm front if it slows, along with training cells. Will need to
monitor for now.

High temperatures in the upper 70s to low 80s Saturday drop into the
mid 70s to around 80 for Monday, then rise into the mid to upper 80s
for Wednesday and Thursday. Low temperatures in the mid 50s to
around 60 Friday and Saturday nights gradually rise into the low 60s
to near 70 for Tuesday and Wednesday nights.
/16

MARINE...
Issued at 350 PM CDT Thu May 9 2024

A moderate onshore flow will persist through early Friday.
Slightly higher winds are expected in the afternoon hours near the
coast in association with an enhanced sea breeze circulation. A
front moves through the marine zones on Friday, allowing for a
light to moderate offshore wind to return for Friday and into
Saturday. /13

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...High Rip Current Risk through late Friday night for ALZ265-266.

FL...High Rip Current Risk through late Friday night for FLZ202-204-
     206.

MS...None.
GM...None.
&&

$$

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