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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS64 KMOB 092117
AFDMOB

Area Forecast Discussion
National Weather Service Mobile AL
416 PM CDT Tue Apr 9 2024

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

.NEAR TERM...
-- Changed Discussion --
(Now through Wednesday Night)
Issued at 416 PM CDT Tue Apr 9 2024

The forecast remains on track for the remainder of the afternoon and
overnight. Upper ridging will linger overhead as the next upper low
pivots out of the Southwestern US and into the Central Plains. Down
at the surface, a persistent southeasterly flow continues to usher
plenty of moisture into the area. Current radar imagery reveals a
few isolated to scattered showers that have developed over interior
portions of southeast Mississippi and southwest Alabama. These
showers are expected to diminish by this evening with mostly dry
and cloudy conditions prevailing tonight. Lows will drop into the
60s.

The next potentially significant weather event will impact our area
Wednesday into Wednesday night with numerous hazards expected. These
hazards include the potential for severe weather, flooding, strong
gradient winds, and multiple coastal hazards. We`ll discuss each of
these impacts in more detail below.

SEVERE POTENTIAL: A potential significant severe weather event is
setting up across the region on Wednesday into Wednesday night. This
is due to a strong shortwave over Texas ejecting east northeast into
the Lower MS Valley and acquiring a negative tilt. As it does so,
deep layer forcing will become maximized over the western portions
of the forecast area Wednesday afternoon and will spread east
through the evening hours. Guidance is in strong agreement that deep
layer wind fields will quickly increase through the day with the
850mb low level jet increasing to 40-50 kt across southeast MS by
18z Wednesday and 50-60 kt in the eastern zones between 00z-06z. An
MCS will likely be ongoing back over Louisiana early to mid
Wednesday morning with the complex maintaining itself and
potentially strengthening as it approaches our western zones by
early afternoon. Surface theta-e values of over 340k are forecast to
nose in on the strengthening low level southerly flow ahead of the
system while 0-1km shear increases to 35-45 kt. Current data
suggests this MCS could sweep across much of our inland forecast
area during the afternoon hours and will carry a threat of
significant damaging wind (up to 80mph) and embedded tornadoes (some
of which could be strong). This is the focus area of the Moderate
Risk issued by SPC. What is more uncertain is if any discrete cells
will develop ahead of this main complex. CAMs are mixed on this
signal, but given the appreciable height falls moving in, it is
certainly a possibility. Such storms would also carry a substantial
tornado threat.

Back to the southeast of the main complex, hi-res guidance indicates
a broken line of storms (potentially supercells) developing
immediately ahead of the cold front and impacting the region from
west to east during the evening hours through about midnight. The
atmosphere will remain very conducive for severe weather, especially
closer to the coast as the strong low level jet continues to advect
in rich low level theta-e within a very favorable low level and deep
layer shear profiles. A significant threat of damaging winds and
tornadoes will exist with this activity as well. The bulk of the
severe weather threat should end around midnight, however, it could
linger til 1-2 am Thursday in our far eastern counties.

The main question and potential limiting factor is the degree of
instability that will be present. HREF mean SBCAPE values are
currently in the 500-1000 J/kg range which would be sufficient for
severe weather given the aforementioned parameters. However, there
is a chance that if too much precip develops earlier than expected
due to the large scale forcing, this could tend to stabilize the
atmosphere prior to the best severe weather parameters moving in.
Something to keep an eye on as we go through time. 34/JFB

FLOODING POTENTIAL: Latest HREF ensemble probabilities of exceeding
3-4" have increased across much of the area with this storm system.
The current forecast is for a general 2-4" but localized totals of 6-
8" cannot be ruled out. This is due to precipitable water values
increasing to over 2" (quite anomalous for this time of year)
combined with the potential for training (especially if convection
becomes focused along a surface boundary enhanced by the MCS cold
pool. The location of the heavier axis of rain is much more
uncertain. Given the uncertainties, but also the potential for
intense rainfall totals in a short time frame, have decided to
include the entire area in a Flood Watch for Wednesday afternoon and
evening. Several rivers are forecast to reach minor stage when
accounting for 3-4" of rain, so any totals higher than this could
result in additional issues. 34/JFB

WIND: A strong onshore flow will develop on Wednesday as the
pressure gradients tightens across the area. A Wind Advisory has
been issued for all inland areas from 11am Wednesday to 8pm
Wednesday for southeasterly winds of 20-30 mph with gusts up to 40-
45mph developing outside of any thunderstorms. The increasing
pressure gradient will also extend over the Gulf Waters and a Gale
Warning remains in effect for all marine zones from late Wednesday
afternoon through early Thursday afternoon with Small Craft
Advisories in effect on either side of the Gale Warning. Winds over
the marine areas are expected to reach 20 to 30 knots with gusts up
to 40 knots and seas building to 6 to 12 ft during this time.

COASTAL HAZARDS: This system will also result in a multitude of
coastal hazards. A high risk of rip currents remains in effect
through late Thursday night with deadly rip currents likely at all
area beaches. Local beach reports from this afternoon have reported
flying red and double red flags and that is expected continue into
Wednesday. A large onshore fetch will also allow seas to build with
high surf conditions expected at all area beaches. A High Surf
Warning is in effect through late Thursday night with large breaking
waves between 4 to 6 feet this afternoon and building to 7-9 feet
(potentially up to 10 feet) by late Wednesday afternoon. With the
increased onshore flow and high surf, there could also be some minor
beach erosion. Coastal flooding is also possible Wednesday morning
and Thursday morning particularly for portions of Northern Mobile
Bay and perhaps near Bayou La Batre given that we are entering into
a springs tide. Based on the current PETSS guidance, I was not
confident enough to issue any coastal flood products, but it is
something that we`ll continue to monitor for. /14
-- End Changed Discussion --





&&

.SHORT TERM...
-- Changed Discussion --
(Thursday through Friday night)
Issued at 416 PM CDT Tue Apr 9 2024

A cold front makes passage late Wednesday and brings an end to the
severe weather. Drier conditions follow for Thursday and Friday as
high pressure moves east over the area. Coastal impacts will take
some time to abate. Highs in the upper 60s/lower 70s Thursday,
warm into the mid 70s Friday. Turning cooler for Thursday/Friday
nights with coolest numbers in the mid 40s positioned over the
interior. /10
-- End Changed Discussion --

&&

.LONG TERM...
-- Changed Discussion --
(Saturday through Tuesday)
Issued at 416 PM CDT Tue Apr 9 2024

High pressure at high altitudes centered over Mexico and the western
Gulf over the weekend maintains west northwest flow aloft.
Surface high pressure moves east across the deep south. Upper
ridging amplifies overhead at the start of the new work week with
some increase in high based clouds possible on southeast edge of
upper trough pivoting northeast across the Mid-MS Valley. With high
pressure aloft and larger scale subsidence, no rain is forecast
through the period.

Daytime temperatures will steadily increase over the weekend as a
more established southerly flow sets up as the surface high moves
east of the area. Will start off cool for morning lows Saturday (mid
40s interior/to lower 50s coast) being some 3 to 7 degrees cooler
than normal heading into mid April. Lows are favored to moderate
each night thereafter. /10
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
Issued at 416 PM CDT Tue Apr 9 2024

An increasing onshore flow will result in Small Craft Advisory
conditions tonight and into Wednesday morning. Winds will continue
to strengthen on Wednesday with Gale conditions beginning late
Wednesday afternoon across the entire marine area ahead of an
approaching front. Gale conditions are expected to persist through
Thursday afternoon in the wake of the frontal passage. Winds will
ease Friday into the weekend as high pressure approaches the
area. /14
-- End Changed Discussion --


&&

.PRELIMINARY POINT TEMPS/POPS...
Mobile      66  75  60  72  49  76  49  80 /   0 100  90   0   0   0   0   0
Pensacola   66  75  64  72  54  75  52  77 /   0  90 100  10   0   0   0   0
Destin      66  75  65  74  57  74  55  75 /   0  70 100  20   0   0   0   0
Evergreen   59  78  60  72  46  75  45  82 /  10  90 100  10   0   0   0   0
Waynesboro  63  74  56  70  46  74  46  81 /  10 100  70   0   0   0   0   0
Camden      60  76  58  68  47  73  45  80 /  10  90  90  10   0   0   0   0
Crestview   60  78  61  76  48  76  45  81 /   0  80 100  20   0   0   0   0

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
AL...Wind Advisory from 11 AM to 8 PM CDT Wednesday for ALZ051>060-
     261>266.

     Flood Watch from Wednesday afternoon through late Wednesday
     night for ALZ051>060-261>266.

     High Rip Current Risk through late Thursday night for ALZ265-266.

     High Surf Warning until 1 AM CDT Friday for ALZ265-266.

FL...Wind Advisory from 11 AM to 8 PM CDT Wednesday for FLZ201>206.

     Flood Watch from Wednesday afternoon through late Wednesday
     night for FLZ201>206.

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

     High Surf Warning until 1 AM CDT Friday for FLZ202-204-206.

MS...Wind Advisory from 11 AM to 8 PM CDT Wednesday for MSZ067-075-
     076-078-079.

     Flood Watch from Wednesday afternoon through late Wednesday
     night for MSZ067-075-076-078-079.

GM...Small Craft Advisory from 7 PM this evening to 4 PM CDT
     Wednesday for GMZ630>636-650-655-670-675.

     Small Craft Advisory from 1 PM to 7 PM CDT Thursday for
     GMZ630>636.

     Gale Warning from 4 PM Wednesday to 1 PM CDT Thursday for
     GMZ630>636.

     Small Craft Advisory from 7 PM Thursday to 1 AM CDT Friday for
     GMZ650-655-670-675.

     Gale Warning from 4 PM Wednesday to 7 PM CDT Thursday for GMZ650-
     655-670-675.
-- End Changed Discussion --

&&

$$

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