Area Forecast Discussion
Issued by NWS Mobile, AL

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000
FXUS64 KMOB 220459 AAC
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1159 PM CDT Sat Oct 21 2017

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

&&

.AVIATION...
06Z issuance...VFR conditions prevail for the remainder of the
night with the exception of MVFR conditions in patchy fog over
interior areas. Showers and storms develop over the western
portion of the area Sunday morning then spread eastward over the
remainder of the area through Sunday evening as a cold front
approaches from the west. Light easterly winds tonight increasing
to 10 to 15 knots Sunday morning and become southeasterly. /29

&&

.PREV DISCUSSION... /issued 922 PM CDT Sat Oct 21 2017/

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

UPDATE...Made slight adjustment to overnight PoPs to account for
the dissipating showers and latest high-res guidance. Otherwise,
the forecast remains on track and no further changes are needed
at this time. /49

PREV DISCUSSION... /issued 626 PM CDT Sat Oct 21 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...
00Z issuance...VFR conditions prevail overnight although some
patchy light fog will be possible over interior areas. For Sunday,
MVFR conditions in showers and storms develop over the western
portion of the area Sunday morning, with the showers and storms
spreading eastward to affect most of the remainder of the area
through the afternoon hours. Easterly winds tonight of generally
5 knots become southeast and increase to 10 to 15 knots Sunday
morning. /29

PREV DISCUSSION... /issued 349 PM CDT Sat Oct 21 2017/

NEAR TERM /Now Through Sunday/...The upper level high pressure
over the southeast Atlantic coast will shift slightly eastward.
Meanwhile, a medium amplified upper level trough extending from
south central Canada to east Texas will shift east over the Great
Plains. Surface ridge of high pressure across the southeast states
will continue to weaken as a weak surface low pressure area or
weak inverted trough forms over the north central Gulf of Mexico.
This pattern will keep a light southeasterly surface wind flow and
low level moisture across the area, with skies varying from
partly cloudy to occasionally mostly cloudy.

The ongoing isolated light rain showers across extreme southwest
Alabama and southeast Mississippi will dissipate through mid evening
with loss of daytime surface heating. Isolated rain showers and
thunderstorms will then increase over the gulf waters and along the
immediate coastal sections after midnight. Shower and thunderstorm
activity will then increase significantly on Sunday ahead of the
approaching upper trough, becoming widespread along and west of
the Tombigbee River, with scattered to numerous coverages to the
east. A few of the afternoon thunderstorms along and west of the
Tombigbee River could become strong to marginally severe as MLCape
values increase to near 1000 J/kg and Sfc-1km SRH values approach
100 m2/s2.

Low temperatures tonight will be around 15 degrees above normal
ranging from 64 to 69 degrees inland areas, with low 70s along the
immediate coastal sections. High temperatures Sunday will be 2 to 5
degrees above normal, ranging from 79 to 84 degrees. /22

SHORT TERM /Sunday night Through Tuesday night/...The latest
(21.12Z) guidance has shown better agreement with the geo-potential
height fields aloft. Will begin the short term with a sharp mid-
level trof axis approaching the Lower MS River Delta Sunday night.
East of this trof, deep layer ascent becomes maximized over the
deep south within an environment that contains anomalously high
deep moisture levels. PWAT`s to increase near 2 inches. A somewhat
faster net eastward progression of the better dynamics and
showers and storms is also seen in the latest guidance over the
central Gulf coast. Still may see some instances of nuisance,
urban type flooding over areas that typically do not drain well in
moderate to heavier rain events. Will maintain storm total QPF at
a range averaging 1 to 2 inches. Although a few pockets of
locally higher amounts are possible, with the faster and more
consistent solutions, the threat of seeing widespread higher rain
amounts above 2 inches Sunday night appears to have been lessened.

As rains move east Sunday night, causing local airmass to
begin to stabilize along with relatively weak low level south to
southwest flow, appears the threat for severe storms going into
Sunday evening trends low. Still could see an occurrence of a few
strong evening storms with potential of producing brief locally
strong wind gusts on the leading edge of the eastward moving
convective band.

Cold front is expected to push across the region Monday morning,
with chances of showers and storms tapering off from west to east
behind the front during the day. With deep layer moisture having
been scoured out by Monday`s frontal passage, a secondary frontal
passage early Tuesday morning comes thru dry but will bring a
more pronounced lowering in deep layer thickness values resulting
in cooler temperatures along with a much drier airmass. Highs on
Tuesday expected to be near seasonal normals for the latter half
of October, ranging in the lower 70s interior to near 75 southern
zones. Overnight lows Tuesday night, much cooler and well below
climo with mid 40s along and north of I-10 and beach areas in the
upper 40s/lower 50s. /10

LONG TERM /Wednesday Through Saturday/...A temperature forecast
into the middle of the upcoming week due to dry deep levels with
surface high pressure diving southward thru Texas Wednesday then
building east over the Gulf Thursday. Coolest daytime highs remain
in the Wednesday time-frame with numbers ranging in the mid/upper
60s for much of the local area. Highs edge slightly higher with each
day thereafter, lifting into the mid to upper 70s by the end of the
medium range. Another unseasonably cool night Wednesday night,
lower/mid 40s along and north of I-10 and beach areas in the upper
40s/lower 50s, will also reflect a moderating trend by heading into
the week`s end, lifting to the mid to upper 50s interior to mid 60s
coast by Saturday morning. A small chance of showers and storms
return to the forecast Friday and Saturday. /10

MARINE...A moderate to strong easterly to southeasterly wind flow
will gradually become southerly through Sunday evening as a cold
front approaches from the west. The front will move across the marine
area on Monday, leading to a moderate to strong west to northwest
flow that persists through midweek. /22

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...High Rip Current Risk through Sunday afternoon for ALZ265-266.

FL...High Rip Current Risk through Sunday afternoon for FLZ202-204-
     206.

MS...None.
GM...Small Craft Advisory until 3 PM CDT Sunday for GMZ650-655-670-
     675.

&&

$$

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