356
FXUS64 KMOB 091004
AFDMOB

Area Forecast Discussion
National Weather Service Mobile AL
504 AM CDT Thu May 9 2024

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

.NEAR TERM...
(Now through Friday)
Issued at 504 AM CDT Thu May 9 2024

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

&&

SHORT THROUGH EXTENDED TERM...
(Friday night through Wednesday)
Issued at 504 AM CDT Thu May 9 2024

Upper ridging will build into the Plains on Friday night in the wake
of the departing shortwave, with flow aloft becoming more
northwesterly over the local area. At the surface, high pressure
will build in into the region, with surface flow becoming
northwesterly as well. This pattern will continue through the
weekend, with persistent northwest flow bringing drier air into
the region. Thus expect mostly clear skies and temps near seasonal
norms (highs in the lower 80s, lows in the upper 50s to lower
60s).

The axis of the upper ridge will slide eastward and through the
forecast area Sunday night, with high pressure along the northern
Gulf. Southerly flow will return to the local area, as the
aforementioned cold front lifts northward through the day on Monday,
in response to a trough moving into the Plains. Showers and
thunderstorms will increase through the day on Monday as the front
lift northwards and several shortwaves eject around the base of the
trough to our west. The trough will move into the Mississippi Valley
Monday night with a surface low and its trailing cold front moving
into the Lower Mississippi Valley. Moisture will continue to
increase as southerly flow strengthens through the vertical column,
with PW values nearing the climatological max for mid May (~2
inches). Showers and thunderstorms will continue through much of the
overnight period Monday, with the greatest chance for thunderstorms
as the cold front moves through on Tuesday. The front will clear the
area Tuesday night as the axis of the trough swings through the
region. Given the day 5/6 timeframe, there is some uncertainty with
regard to the timing and overall impacts which will be further
refined as it gets closer.

Flow aloft will then become zonal, with southerly surface
flow quickly returning. Despite the confidence of the cold front
making it through the area, we won`t see much of a change to the
pattern, as the southerly surface flow combines with the zonal flow
aloft to lend hot and humid conditions towards the latter half of
the week. /73

&&

.MARINE...
Issued at 504 AM CDT Thu May 9 2024

A moderate onshore flow will persist through Friday morning as a
cold front approaches the area. Strong to severe thunderstorms are
possible ahead of the front late Thursday night and into early
Friday morning. The front is expected to move through the marine
zones by Friday afternoon, allowing for a light to moderate
offshore wind to return for Friday and into Saturday. /73

&&

.PRELIMINARY POINT TEMPS/POPS...
Mobile      88  71  87  60  84  62  81  64 /  20  40  50   0   0   0  10  20
Pensacola   87  73  86  63  82  64  80  67 /  20  40  60   0   0   0  10  20
Destin      83  75  84  66  82  66  81  69 /  20  30  70   0   0   0   0  10
Evergreen   89  69  85  56  81  56  82  59 /  60  80  70   0   0   0   0  10
Waynesboro  90  66  85  56  81  57  81  60 /  40  80  30   0   0   0   0  20
Camden      88  66  83  55  79  56  80  59 /  60  80  50   0   0   0   0  20
Crestview   87  70  86  58  84  57  83  60 /  30  50  70   0   0   0   0  10

&&

.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.
&&

$$

This product is also available on the web at:
www.weather.gov/mob