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fxus64 kmob 220513 

Area forecast discussion
National Weather Service Mobile Alabama
1213 am CDT Tue Oct 22 2019

Discussion...updated for latest aviation discussion below.


06z issuance...expect a mix of MVFR and IFR ceilings to occur
overnight ahead of a cold front approaching from the northwest.
Skies are forecast to become clear around 22.12z across the
Mobile Metro area, and around 22.15z across the Pensacola Metro
area in the wake of the cold front. Winds will continue from the
south to southwest, or light and variable, ahead of the cold
front. Winds will then shift to the northwest and increase to 10
to 15 knots in the wake of the cold front. /22


Previous discussion... /issued 851 PM CDT Mon Oct 21 2019/

Discussion...see updated information for land and marine areas below.

Update...the convective line will move east out of the northwest
Florida coastal waters shortly. With that, the severe weather threat
has ended. Given radar trends, pops will continue to be adjusted
downward. Highest rain chances for a bit longer reside southeast
of I-65, but this activity will also begin decreasing in coverage
before midnight. Any late night activity will be over the eastern
zones in the form of light showers with any additional rainfall
amounts generally less than a tenth of an inch at best. Cold
front was aligned along the lower MS River Valley. The front
advances eastward and makes passage during the pre-dawn hours,
bringing drier and cooler weather in its wake.

Previous discussion... /issued 701 PM CDT Mon Oct 21 2019/

Discussion...see updated information for land areas and aviation
discussion below.

Update...7 pm: a steady and quick eastward motion to the rain
shield continues. The leading edge of the deep convection will be
moving eastward over the northwest Florida coastal sections this
evening out 60 nautical miles offshore. Instability is highest
over the marine area where sbcapes range from 1500 to 2500 j/kg,
atop this instability effective bulk shear magnitudes range from
45 to 55 knots east of the line. Considering degree of instability
and shear, appears the main threat remains over the coastal
waters with strong to perhaps damaging wind gusts maintaining a
threat to recreational and commercial boaters. Radar has shown a
few weak transient rotational Couplets on the leading edge of the
marine convective line which could spawn occurrences of
waterspouts in addition to winds in excess of 34 kts. /10

Previous discussion... /issued 616 PM CDT Mon Oct 21 2019/

Discussion...see updated information for land areas below.

Update...back edge of rain shield is moving eastward at a fairly
fast clip around 35 kts, having moved out of interior southeast MS
zones and now crossing over southwest Alabama southward out of the Alabama
coastal waters. Forecasters will begin to taper back pops from
west to east given these trends. Meso-analysis shows the bulk of
available instability (sbcapes 1500 to 2500 j/kg being confined
over the northwest Florida Panhandle southward over the marine area.
This is where radar shows the eastward motion of the leading edge
of deepest convection. Given orientation of the better instability
and radar trends, the severe weather threat has been cut way back
in areal extent with slight risk lowered to a marginal risk from
Okaloosa co. Florida westward to Baldwin co. Alabama. The main impacts from
potential of strong winds and dangerous to potentially deadly
lightning remains over the coastal waters and perhaps closer to
the beaches. /10

Previous discussion... /issued 401 PM CDT Mon Oct 21 2019/

Discussion...updated for latest marine discussion below.

Marine...a Small Craft Advisory is now in effect for the open
Gulf waters of Alabama and nwfl out to 60 nm including the lower end of
Mobile Bay and MS sound east of Pascagoula beginning early
Tue morning continuing through early Tue evening. Expect northerly
winds increasing to 18 to 23 knots in the areas with seas
building to 4 to 6 feet offshore and around 2 feet in Mobile Bay
and MS sound. 32/ee

Previous discussion... /issued 341 PM CDT Mon Oct 21 2019/

Near term /now through tonight/ early this evening most of
the heavier showers and thunderstorms will be over the eastern
half of the forecast area or generally east of a line stretching
from Thomasville to Gulf Shores in Alabama including all locations in
the western Florida Panhandle. Thunderstorms will continue to decrease
in coverage and intensity mostly due to the lost of daytime
heating and better forcing aloft that shifts off to the northeast,
though we still can't rule out a few strong storms below severe
limits occurring mostly before midnight. By around midnight or
shortly before a cold front begins to move into northern and
western sections of the forecast area moving off the coast before
sunrise. Expect a moderate northerly flow in the wake of the front
slowly diminishing after sunrise. Temperatures will range from
the lower to middle 50s north of the front, or northern and
western the sections of the forecast area, and the upper 50s to
middle 60s south and east of the front which includes most areas
generally along and east of the I-65 corridor inland and most
locations along the immediate coast. 32/ee

Short term /Tuesday through Thursday night/...a large upper trof,
the axis of which extends from the western Great Lakes to the
lower Mississippi River valley, takes on a negative tilt through
Tuesday night while lifting into the northeast states. A nearly
zonal flow develops over the southeast states Tuesday night, then
another upper trof amplifies over the central states through
Thursday. A dome of cool and dry high pressure builds into the
region through Tuesday night in the wake of a cold front which
moved through in the near term period. Another cold front develops
over the plains on Wednesday in response to the central states
upper trof, and an inverted surface trof also develops over the
far western Gulf by Thursday night. It is not clear how far
eastward the frontal boundary will be able to progress during this
evolution, though a consensus has the front making it into
northwest Mississippi to western Louisiana by late Thursday
night. Light northeasterly winds on Wednesday become easterly on
Thursday and continue into Thursday night as the surface high
gradually retreats from the area ahead of the approaching front.
An overrunning southerly flow aloft sets up on Thursday and
continues into Thursday night with precipitable water values
increasing to 1.5 to 1.75 inches. While dry conditions are
expected through Wednesday night, this overrunning pattern and
increasing deep layer moisture will support a return of small pops
near the coast Thursday afternoon followed by likely pops for most
of the area Thursday night. Highs on Tuesday and Thursday range
from around 70 well inland to the mid 70s over the southern
portion of the area, and Wednesday will be a bit cooler with upper
60s well inland ranging to lower 70s elsewhere. Lows Tuesday
night range from the mid 40s well inland to the lower 50s at the
coast then moderate slightly Wednesday night before milder
temperatures follow for Thursday night with mid 50s to lower 60s
inland ranging to mid 60s at the coast. A high risk of rip
currents continues through Tuesday evening then a moderate risk of
rip currents follows through Thursday. /29

Long term /Friday through Monday/...there are two different potential
outcomes with the central states upper trof for Friday into
Saturday. The first possibility is the upper trof slowly weakens
while advancing across the eastern states, and the second is that
a cut off upper low forms over Texas. If the cut off low
materializes, then a surface low evolves from a western Gulf
inverted trof and moves well north of the region, bringing a
weakening cold front into the forecast area on Sunday which then
stalls. Should the cut off low not develop, then the cold front
will move through the area much earlier, on Friday. Fortunately,
both solutions have some form of an overrunning pattern over the
area on Friday which supports likely to categorical pops. By
Saturday, large differences develop between the potential outcomes as
dry conditions would be expected to develop if the cold front
moves through on Friday, while otherwise some mention of pops will
be needed through the remainder of the period. Due to the
uncertainty, have gone for now with chance pops on Saturday with
slight chance to chance pops on Sunday and Monday. Highs on
Friday and Saturday will be in the mid 60s to lower 70s along and
west of I-65 and in the lower to mid 70s east of I-65. A warming
trend ensues on Sunday, and by Monday highs will be in the mid to
upper 70s. Lows Friday night range from the lower to upper 50s
west of I-65 to the upper 50s to lower 60s east of I-65, then
trend gradually warmer with lows Sunday night mostly ranging from
around 60 inland to the mid 60s at the coast. /29

Marine...a cold front will continue to approach from the northwest
this afternoon. Ahead of the front scattered to numerous showers and
thunderstorms can be expected with a few strong storms possible late
this afternoon and this evening. In the wake of the front a moderate
to strong northerly flow can be expected Tue through Wed. A moderate
easterly flow will develop late Wed night and continue through Thu
as a broad surface ridge of high pressure builds along the eastern
Seaboard combined with another cold front approaching from the west.


Mob watches/warnings/advisories...
Alabama...high rip current risk through this evening for alz265-266.

Florida...high rip current risk through this evening for flz202-204-206.

GM...Small Craft Advisory from 7 am this morning to 7 PM CDT this
evening for gmz631-632-650-655-670-675.


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