Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 261116 AAB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
616 AM CDT Tue Sep 26 2017

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


12Z issuance...Few to scattered cig bases at MVFR categories this
morning with tsra potentially in the vcty of MOB and BFM by
around 26.17Z. Away from convection. Light north to northeast
winds become southeast into the afternoon. /10


.PREV DISCUSSION... /issued 344 AM CDT Tue Sep 26 2017/

NEAR TERM /Now Through Tuesday night/...Upper air analysis this
morning shows a short wave mid level ridge over the western Gulf,
poking northward into the Mid-South. East of the ridge, high
level trof has slipped southeast and is more positioned over the
northeast Gulf. Satellite Total Precipitable water product shows
a narrow zone of better deep layer moisture (1.6 to 1.8 inches)
aligned over the southwest half of the local area, with lower
values (1.3 to 1.5 inches) over the far northeast zones. Considering
where the better moisture axis is, passage of weak mid level
impulses that ease southward between the upper ridge to the west
and trof to the southeast aiding in ascent, forecasters call for
isolated to scattered showers and storms generally along and south
of a line from Waynesboro MS to Milton FL today. A few storms
potentially strong, with brief strong wind gusts and frequent
lightning being the main threats. Any lingering showers and
storms that may carry over into the evening over the southwest
zones looks to dissipate by 9 PM.

Daytime highs generally 4 to 8 degrees above climatology, ranging
from the upper 80s to lower 90s along and north of I-10 to mid
80s at the beaches. Overnight lows also above normal, ranging from
the mid to upper 60s interior to lower to mid 70s beaches. /10

SHORT TERM /Wednesday Through Thursday night/...The northern
extent of an upper ridge extending from near the Texas coast to
near the Ohio river valley retreats southward during the period in
response to a large upper trof which gradually builds into the
Great Lakes region. A surface low well to the north, associated
with the upper trof, brings a trailing cold front into the
southeast states on Wednesday, then slowly through the forecast
area through the remainder of the period as a large surface high
over the Plains begins to build into the eastern states.  During
this evolution, the upper trof also begins to phase with a weak
upper trof lingering over the extreme southeast states. This
pattern maintains a weak deep layer northerly flow over the
forecast area during the period along with modest subsidence, and
despite the frontal passage the result will be a dry forecast.
Will have highs on Wednesday and Thursday in the lower 90s except
for near 90 at the coast. Lows will range from the mid to upper
60s inland to the lower 70s at the coast. /29

LONG TERM /Friday Through Monday/...The large upper trof near the
Great Lakes region partially phases with the weak upper trof over
the extreme southeast states, with the combined feature moving
off into the western Atlantic through the weekend. The upper ridge
oriented from the Texas coast into the lower Mississippi river
valley expands greatly northward into the eastern states, while
the large surface ridge completes building into the eastern
states with the flow over the forecast area gradually switching
from light northerly to easterly.  Will continue with a dry
forecast on Friday, then expect to see a return of small pops for
the eastern portion of the area on Saturday then most of the area
on Sunday as the easterly flow brings a region of elevated deep
layer moisture across the area. Have gone with small pops near the
coast on Monday as while the easterly flow continues, drier air
also begins to flow mainly into the interior portion of the area.
The previously warm afternoon highs in the lower 90s on Thursday
(which were about 7-9 degrees above normal) gradually trend to
seasonable values mostly in the lower 80s during the period.
Overnight lows will range from the lower 60s inland to near 70 at
the coast. /29

MARINE...A weak pressure pattern results in a light and
variable wind flow pattern and small sea states through the middle
of the week. A more established north to northeast flow is
forecast by the end of the week as a frontal boundary makes
passage late Thursday. Seas to trend higher over the weekend. /10




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