954
FXUS64 KMOB 091718
AFDMOB

Area Forecast Discussion
National Weather Service Mobile AL
1218 PM CDT Thu May 9 2024

...New AVIATION...

.AVIATION...
(18Z TAFS)
Issued at 1205 PM CDT Thu May 9 2024

General VFR conditions with local mid MVFR conditions in isolated
to scattered rain showers and thunderstorms are expected this
afternoon into this evening. Conditions will deteriorate tonight
as several rounds of convection move across the area beginning
this evening. A cold front will sag south across the area Friday
morning, bringing low end MVFR/IFR conditions to the area Friday
morning. Southerly winds of 10 to 15 knots with locally variable
winds near the convection will shift to westerly overnight, then
northwest to northerly Friday morning as the front passes. /16

&&

.NEAR TERM...
(Now through Friday)
Issued at 1205 PM CDT Thu May 9 2024

No changes made at this time.

******************** previous issued at 504 AM CDT *********

Multiple rounds of strong to severe storms are possible with
confidence in a potentially significant severe weather event
Thursday night is increasing.

Synopsis...Broad southwesterly to westerly flow associated with a
large cutoff low over the four corners, a digging trough over the
Great Lakes and a rather flat ridge of high pressure over the
Gulf of Mexico. This pattern is expected to persist throughout the
period with two subtropical impulses embedded within the broader
flow. Rain chances will be centered around these two impulses, the
first of which will pass through during this afternoon. Scattered
to potentially numerous thunderstorms will develop along a slowly
sagging outflow boundary across interior south central Alabama. A
couple of storms could become strong to severe. Storms will also
re- enforce the already established outflow boundary/surface cold
front further south ahead of the next wave. This next impulse will
be the big punch as it quickly zips across the deep south. Storms
will develop ahead of this impulse across Louisiana and
Mississippi during the late afternoon into the evening and cluster
into a complex of storms. This complex of strong to severe storms
are expected to move through the area around midnight to slightly
before midnight. There are uncertainties on location of where
this complex of storms will move and the severe potential of this
round. By Friday midday, the final shortwave will pivot around the
Great Lakes trough sparking off one last round of storms mainly
across coastal Alabama into the northwestern Florida Panhandle
before the boundary finally pushes offshore.

Severe Weather...Multiple rounds of strong to severe storms are
Thursday through Friday with the overnight storms having the highest
potential ceiling. Round one will likely occur this afternoon across
far interior south central Alabama along the slowly sagging outflow
boundary. We are a bit on the edge of the best forcing aloft which
may keep storms more scattered in nature. However, strong deep layer
winds will support supercells with effective shear around 45 to 50
knots. On top of that, strong instability is expected during the
afternoon with MLCape values around 3000 to 3500 Joules/KG. Strong
storm relative inflow around 30 knots with weak low level shear and
strong instability within the hail growth zone will likely support
potentially large hail approaching golf balls with any supercells
that do mature. A conditional tornado threat is possible; however,
given relatively moist low levels below 700 mb and warm temperatures,
downdrafts will be fairly warm and weaker likely struggling to
balance strong storm relative inflow. Typically in this environment
clustering will be needed but there is just enough low level storm
relative helicity to support a tornado threat IF storms can some
help or  a nudge from a storm merger/cold pool influence. Basically
going to need supercells to cluster up vs a more discrete mode to
get a tornado threat and even then it`s going to be difficult given
the poor low level shear. Nonetheless, cannot rule out a potential
tornado. Damaging winds will also be possible with stronger
supercells and supercell clusters.

Round two will probably be the more significant round as the next
shortwave moves through. Storms will mainly start well west of the
area during the late evening and quickly evolve into a thunderstorm
complex or MCS for short. This MCS will quickly accelerate eastward,
driven by a rather strong cold pool. Instability overnight will
remain well above 3500 J/KG as drier air advects into the midlevels.
Drier air will also allow for more intense downdrafts to develop
further supporting the potential of a rather potent MCS. The big
question is where does it go and how strong does it get. This will
likely be highly dependent on how this afternoon goes and where the
remnant outflow boundary is located. High resolution guidance has
steadily come to a better agreement that we are likely in big
trouble as the outflow boundary sets up across the highway 84
corridor. If this sets up around there then this MCS will likely
travel across most of our area. 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 could not be ruled out; however, low level shear might be
a little too weak to really get the QLCS tornadoes going.
Nonetheless, the upper ceiling of damaging wind gusts being modeled
by high resolution guidance would be significant enough without the
tornadoes. 80+ mph winds is still 80+ mph winds and should be taken
seriously. Now for the caveat! If the outflow does not make it to
our area or it surges offshore this will either 1. potentially allow
for the worst to pass north of the area (least likely scenario) or
2. the MCS runs into a much more stable environment and it just
rains over the area (possible but not much confidence in this
scenario but fingers crossed). Either way we need to be on guard
overnight tomorrow as this event could have a rather high damaging
wind ceiling. If this ceiling looks to come to fruition then further
adjustments to the severe threat may be needed this afternoon.

Finally one more round of isolated to scattered strong to severe
storms will be possible early Friday afternoon. This round is a bit
more marginal and highly dependent on the overnight storms. The
question at hand is does the overnight storms overturn the
atmosphere and keep storms from developing. IF storms do develop in
the afternoon they will likely be slightly elevated as the outflow
from the overnight storms should push offshore. Given still strong
deep layer shear profiles and strong instability within the hail
growth zone with deep separation from the freezing level to
equilibrium level, large hail would be the main hazard Friday early
afternoon across coastal Alabama and into the Florida Panhandle. If
storms are able to fire, would not be surprised to see a larger
hailstone or two as storms intensify. We just are not confident
storms will be able to go in the wake of the MCS and at the time we
are still unsure exactly where that MCS will go in the first place.
Thus this round is more of a wait and see.

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

Heavy Rainfall...While rain rates within storms will be heavy, the
overly potential for flooding rain appears low. These shortwaves
appear to move way to fast through the flow to actually setup a long
duration training scenario and with the fast moving cold pool driven
MCS expect rain to be heavy but not long enough to overcome
impressively dry antecedent conditions. Outside of an urban area or
two and the potential for a localized training storm, the flash
flood risk appears to remain rather limited and localized. BB/03

&&


.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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