FXUS64 KMOB 261130 AAA

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
630 AM CDT Wed Apr 26 2017

.DISCUSSION...Updated for latest aviation discussion below.


12Z issuance...VFR conditions will prevail through much of the
period, with MVFR cigs expected to develop during the late
afternoon. Southerly winds will increase with gusts to around 20
knots by this afternoon. Rain chances increase late in the period
as a cold front approaches from the west. /13


.PREV DISCUSSION... /issued 445 AM CDT Wed Apr 26 2017/

NEAR TERM /Now Through Thursday/...A dry and stable airmass will
remain over the area today as upper and sfc ridging remain
intact. Meanwhile, an upper trough will dig across the central
plains and become negatively tilted as it ejects northeast through
the afternoon and evening hours. Ahead of the trough, a sfc low
will move from the Arklatex to the Ohio Valley by this evening
with a trailing cold front approaching the Mississippi River by
00Z this evening. A line of showers and thunderstorms is expected
to be ongoing along the front as it moves eastward overnight and
into the the western portions of our area around midnight. The
front will move east of the area by late morning on Thursday as it
begins to stall out. Parameters are most favorable for a few
strong to severe storms between 06-09Z across primarily
northwestern areas.

The upper dynamics will rapidly pull northeast away from the area
overnight. This will lead to a weakening trend in convection as it
moves across. Damaging winds will be the primary threat as the
primary convective mode is expected to remain linear. The stronger
cores may also produce some large hail. Showers and thunderstorms
will continue east through the day on Thursday and likely linger
across eastern zones Thursday afternoon as the front begins to
stall. The severe threat is expected to continue to decrease as
the dynamics pull away with just a marginal risk continuing. Highs
are expected to be in the low to mid 80s away from the coast with
upper 70s along the coast. Lows tonight will fall into the low
60s across northwest areas to low 70s along the coast. /13

SHORT TERM /Thursday night Through Friday night/...A southwesterly
flow pattern aloft will prevail across our forecast area during
the Thursday night through Friday night time frame between an
upper level ridge of high pressure building over the FL Peninsula
and adjacent western Atlantic Ocean and the next broad upper
level trough that will be deepening over the western CONUS.
Southerly low level flow will return to the region Thursday night
and continue through Friday night between the surface ridge over
the western Atlantic and the next deepening low pressure system
over the Plains states. Low level warm advection should allow
surface dewpoints to rise into the upper 60s to lower 70s through
Friday night. There also could be isolated showers and
thunderstorms develop in the warm advection regime Thursday night
into Friday, but confidence in measurable precipitation and
expectance of low coverage was enough to keep POPs below 20% with
this forecast. Later shifts may need to revisit and add at least
some isolated convective mention either Thursday night into
Friday if later model trends lend greater confidence. Lows
Thursday night will range from the mid 60s to around 70 inland to
the lower 70s near the coast. Highs Friday should warm into the
mid to upper 80s inland, and potentially around 90 over a few
spots. Readings near the coast should range in the upper 70s to
lower 80s. Lows Friday night will trend a little warmer with
readings around 70 to the lower 70s across the region. /21

LONG TERM /Saturday Through Tuesday/...The next deep upper level
trough will move across the central and southern Plains states
Saturday, before lifting toward the Upper Midwest Sunday night
into early Monday. An associated surface cold front will advance
eastward toward the Mississippi River Valley Sunday, then across
our forecast area late Sunday night into Monday morning. Enhanced
deep layer moisture and synoptic scale lift along the frontal zone
will favor an organized complex/line of showers and thunderstorms
spreading eastward from the Mississippi Valley Sunday morning to
the central Gulf Coast region late Sunday afternoon into late
Sunday night/early Monday morning. There are still some timing
differences noted, but trends currently favor showers and
thunderstorms impacting our southeast MS and interior southwest AL
counties either late Sunday morning or early Sunday afternoon,
with convection slowly spreading eastward across the forecast area
through Sunday evening/night, before gradually clearing our
eastern zones by late Monday morning. There are indications of a
rather strong low level jet developing across our forecast area
ahead of the line, potentially as strong as around 40-55 knots
(stronger toward southeast MS and interior southwest AL) Sunday
morning into early Sunday afternoon. The strong LLJ in conjunction
with favorable deep layer shear, good instability with MLCAPE
values between 1000-1500 J/KG, and 0-1km storm relative helicity
values between 150-250 m2/s2 on average will favor potential for
embedded severe storms moving across the region Sunday into Sunday
night, with all severe modes possible. Very heavy rainfall may
also accompany the line, with potential of at least 1-3 inches of
rain with locally higher amounts. A drier zonal flow returns
Monday afternoon into Tuesday in the wake of the departing system.

MARINE...Southerly winds and seas will build late today in
response to an approaching cold front. Showers and thunderstorms
will move across the marine area tonight into early Thursday.
Winds and seas will rebuild late in the week into the weekend as a
stronger cold front approaches from the west. /13


AL...High Rip Current Risk through Thursday morning for ALZ265-266.

FL...High Rip Current Risk through Thursday morning for FLZ202-204-

GM...Small Craft Advisory from 4 PM this afternoon to 7 AM CDT
Thursday for GMZ631-632-650-655-670-675.



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