Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 220159 AAB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
859 PM CDT Mon Aug 21 2017

.DISCUSSION...See updated information for land areas below.


.UPDATE...Convection has faded away this evening with only
a few areas of light stratiform rain left over. Almost all areas
are expected to be dry in a few hours with a quiet overnight
expected. Cannot rule out an isolated shower or storm along the
coast in the predawn hours with precip waters hovering around 2
inches and an upper low to our southwest which will allow a few
storms to develop offshore during the marine diurnal max and
potentially impact areas close to the coast. Also cannot rule out
some patchy fog overnight, but currently not expecting anything

Just sent the forecast update to lower rain chances for the rest
of the evening as well as adjust temps/dewpoints based on
observations. 34/JFB


.PREV DISCUSSION... /issued 658 PM CDT Mon Aug 21 2017/

DISCUSSION...Updated for latest aviation discussion below.

00Z issuance...Lingering isolated to scattered SHRA/TSRA will
impact portions of the region early this evening before a gradual
diminishing trend is expected through the next couple of hours.
Additional scattered storms will develop near the immediate coast
Tuesday morning and develop inland through the day. Localized
MVFR conditions and gusty winds will be possible near the stronger
storms. VFR otherwise prevails through the forecast period. /21

PREV DISCUSSION... /issued 408 PM CDT Mon Aug 21 2017/

NEAR TERM /Now Through Tuesday/...Broad upper low centered over
the north central gulf south of the mouth of the Ms river this
afternoon will continue to shift west through tonight leading to
deeper moisture in the boundary layer this afternoon through early
Tue afternoon then slowly decreasing from east to west later in the
day. Increased lift or mid level forcing is noted with this pattern
as several vort lobes continue to rotate counter-clockwise around
the main low center helping to generate the better coverage of
showers and thunderstorms across most of the lower half of the
forecast area this afternoon and this evening, shifting south over
the adjacent gulf waters overnight and early Tue, then forming over
coastal areas by mid to late morning, spreading further inland with
a weak seabreeze circulation by early to mid afternoon. For now the
best coverage for daytime convection on Tue will be over northern
and western sections of the forecast area by mid to late afternoon
as enhanced lift ahead of the weak seabreeze boundary moves
northward across these areas during max heating in the afternoon.
Model soundings depict the deeper moisture across most of the
forecast area tonight through Tue with marginal lapse rates in the
boundary layer through the period suggesting the main threat with
the stronger thunderstorms will be gusty straight line winds around
40 knots or less...very heavy rainfall with maybe some nuisance type
flooding locally and frequent cloud to ground lightning. For later
this evening and overnight skies will become partly cloudy to the
north inland from the coast with better clouds remaining over
coastal areas stretching well offshore. Some patchy fog will also be
possible over inland areas generally along and north of the I-10

With a better moisture across the region lows tonight will be a tad
warmer than last night ranging from the lower to middle 70s for most
inland areas and the mid to upper 70s along the immediate coast.
With better clouds tomorrow compared to last weekend highs Tue will
be a tad cooler climbing to the lower to middle 90s for most inland
areas and the upper 80s to near 90 near the immediate coast. 32/ee

SHORT TERM /Tuesday night Through Thursday night/...High
pressure builds into the central and northern Gulf as the upper
tropospheric trough moves west and settles over the western Gulf,
where it remains for the duration of the short term. To the
north, a longwave trough over the Great Lakes deepens
southeastward over the Appalachian spine, pushing a weak surface
front south before stalling it just north of the local area.
South of this front, a hot and humid summertime airmass
characterized by PWATs around 2.0 inches will set the stage for a
series of upper shortwaves rotating around the base of the
longwave trough to kick off scattered showers and thunderstorms
each day through the short term period. Given the return of more
substantial deep-layer moisture and instability, as well as the
additional upper dynamics provided by the passing shortwaves,
storms could become strong enough to produce gusty winds, frequent
lightning, and heavy downpours. Temperatures continue to run
around or slightly above seasonal, with highs in the low 90`s and
lows in the mid 70`s. /49

LONG TERM /Friday Through Monday/...We continue to see a wet
pattern over the weekend as high pressure remains over the
southern and central Gulf and a series of impulses rotate around
the upper trough to our north and act on a moist and unstable
summertime airmass. Some of these storms could become strong
enough to produce gusty winds, frequent lightning, and heavy
downpours. The forecast heading into early next week remains
highly uncertain at this time, as models are struggling to resolve
what will happen with the remnants of Harvey as they move onshore
somewhere in Mexico or far southern Texas. The Euro remains the
much wetter solution, stalling the system over southern Texas
before it gets caught up in another mid-latitude trough digging
into the eastern CONUS, eventually pushing it northeast up the
Gulf coast and towards the local area. This would mean very wet
weather for us early next week. Meanwhile, the GFS pushes the
remnants of Harvey well inland into central Texas where it
eventually dissipates, leaving an eastern seaboard trough open to
push drier air into our area from the northeast, keeping our
weather clear and dry. Thus, model trends over the course of this
week will warrant close monitoring as the Harvey situation in the
Bay of Campeche unfolds and the models are able to grab a better
handle on what will happen with its leftovers.

Expect the weekend to remain around seasonal in terms of
temperature, with afternoon highs reaching the upper 80`s to low
90`s areawide and overnight lows ranging from upper 60`s to low
70`s inland and mid to upper 70`s along the coast. /49

MARINE...Weak high pressure will continue to build west over the
north central gulf through the week leading to mostly a light east
to southeast wind flow through early Tue afternoon, shifting mostly
southwest to west by late Tue afternoon then remaining mostly
northwest to southwest through the remaining of the week as the
surface ridge settles further west over the north central gulf.
Expect mostly scattered coverage of showers and thunderstorms
through the remainder of the week with the best chance of
measurable rain occurring during the overnight and morning hours
through the forecast period. Most of the stronger thunderstorms
will be accompanied with gusty straightline winds around 30 knots
or less, frequent lightning, very heavy rainfall and choppy to
rough seas. 32/ee




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