Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 230200 AAA
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
800 PM CST Thu Feb 22 2018

.DISCUSSION...Updated for latest marine discussion below.

&&

.MARINE...Did a quick update to the current marine forecast
mostly to reflect current wind conditions a little better for this
evening and introduce fog over the near shore waters earlier than
anticipated. The best chance for widespread fog, possibly
becoming dense before sunrise, will be over the near shore waters
of Al generally from Gulf Shores stretching west to the MS/AL
border. 32/ee

&&

.PREV DISCUSSION... /issued 611 PM CST Thu Feb 22 2018/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...
00Z issuance...MVFR cigs and visibilities through about 23.04z
followed by IFR to LIFR cigs and visibilities through about
23.13z followed by MVFR to VFR conditions through through 24.00z.
Winds will be southeast at 3 to 7 knots through 23.14z increasing
to 6 to 10 knots through 24.00z. 32/ee

PREV DISCUSSION... /issued 405 PM CST Thu Feb 22 2018/

NEAR TERM /Now Through Friday/...Weather maps today continue to
show a long wave trof over the western US with an anomalously
strong mid level ridge axis holding firm off the southeast US
coast. 22.12Z analysis indicates that the western periphery of
the H50 ridge has strengthened over the past 24 hrs, with height
rises on the order of 10 to 30 meters over the central Gulf coast
during this time period. The strength of the ridge aloft, dominating
the southeast US, lies some 2 to 3 standard deviations above the
mean for this time of year. At the surface, a quasi-stationary
frontal boundary, aligned generally parallel to the high level
southwest flow, was draped from the Virginias southwest to off the
east Texas coast. The front well to the west has been the focus of
highest probabilities of measurable rains of late. Very little
change in the upper air pattern holds into tonight. Surface ridge of
high pressure from the western Atlantic, westward into the southeast
US maintains a light southeast flow and a moist boundary layer,
supporting the re-development of fog and low clouds overnight. This
is supported by the latest short range ensembles/HRRR/RAP and NAM12
guidance. Fog could become locally dense late in the night in some
areas. Unseasonably warm overnight lows persist.

Friday, upper ridge to the east narrows somewhat from off the
southeast US coast into the Gulf. Some potential exists for mid
level energy, caught up in the southwest flow aloft operating on
daytime instability and sufficient deep layer moisture, may be
enough to bring a chance of showers and perhaps a few storms by
Friday afternoon over the western half of the local area. Before
then, daytime highs could approach record territory once again for
some areas. /10

SHORT TERM /Friday night Through Sunday night/...Southwesterly
mid level flow will strengthen across the central Gulf Coast
region Friday night into Saturday as a potent mid level shortwave
trough lifts from the Rocky Mountains to the central Plains. An
associated area of surface low pressure will also deepen and lift
from the central Plains Saturday morning and toward the vicinity
of Missouri and Iowa by late Saturday afternoon. Warm and moist
southerly surface flow will persist across our region into
Saturday in advance of this feature and also to the west of the
strong deep layer ridge of high pressure over the western Atlantic
and southeastern U.S. Expect a continuation of much above normal
temperatures Friday night into Saturday, with potential for
additional near record or record temperatures during this time
frame. An embedded shortwave impulse in the southwest mid level
flow will translate across Mississippi and southwest Alabama
Friday night, and an associated increase in layer moisture and
ascent will support the development of isolated to scattered rain
showers, primarily across the western portion of the forecast
area. Additional impulses in the southwest flow aloft are set to
propagate across western and northern portions of the region
Saturday, bringing an additional chance of showers and a few
thunderstorms to the region. MLCAPE values still look to increase
to 300-800 J/KG across southeast Mississippi and interior portions
of southwest Alabama Saturday afternoon/early Saturday evening,
while low level/850 mb flow strengthens to around 35-40 knots over
this same region. Any convective cells that develop in this
environment would have the potential to become strong to
marginally severe. SPC Day 3 Outlook has a marginal risk of
severe storms outlined over this portion of the region, which
looks reasonable.

We may see a brief lull in activity mid to late Saturday evening
before a more organized line of convection approaches interior
southeast Mississippi and interior southwest Alabama after
midnight ahead of the approaching cold front. An isolated strong
to severe storm will be possible within the line over our
interior northwest zones, but there will be an overall decreasing
trend in instability and shear after midnight. Rain chances will
remain high going into Sunday and Sunday night as plentiful
moisture and lift spread across our region along the slow moving
frontal zone. We have likely to categorical POPs over much of the
region during this time frame. Isolated thunderstorms also remain
possible given weak instability. Slightly cooler temperatures are
expected Sunday and Sunday night, though still remaining quite a
bit above normal. /21

LONG TERM /Monday Through Thursday/...The cold front finally
pushes southeast of the region Monday. A lingering good chance of
showers continues Monday morning before quickly decreasing from
northwest to southeast Monday afternoon into Monday evening as a
much drier airmass spreads into the area in the wake of the front.
Drier weather is expected Monday night along with noticeably
cooler temperatures, before rain chances increase Tuesday and
Tuesday night ahead of the next approaching shortwave trough. Best
rain chances Wednesday look to be favored over interior areas.
Another shortwave trough and associated cold front could then
bring the next round of showers and possibly a few storms
Thursday. Above normal temperatures are expected Tuesday through
Thursday. /21

MARINE...Main hazard in the near term would be reduced overnight
visibility in fog, re-forming near bays and sounds. Over the
weekend, an increased chance of showers, along with a few embedded
storms expected as a frontal boundary sinks closer to the coast.
Winds, waves and seas will be locally higher in and near any
isolated storms along with an increased lightning hazard. /10

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...None.
FL...None.
MS...None.
GM...None.
&&

$$

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