Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 220000

Area Forecast Discussion
National Weather Service Mobile AL
600 PM CST Wed Feb 21 2018

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


22/00Z issuance...A persistent and slightly building ridge, surface
and aloft, to the east of the region maintains a well established
low level southeasterly flow through the next 24 hours. Winds gusty
at times, especially during the afternoon hours. Ceilings at MVFR
categories this evening and MVFR to VFR on Thursday, but dropping
to IFR at times overnight with the potential of patchy fog. Isolated
SHRA early this evening, otherwise a rainfree forecast. 12/DS


.PREV DISCUSSION... /issued 405 PM CST Wed Feb 21 2018/

NEAR TERM /Now Through Thursday/...Unseasonably warm and a
potentially record breaking temperature pattern continues in the
near term along the central Gulf coast. Upper air map analysis
shows a highly amplified pattern with a long-wave trof over the
western half of the CONUS while a deep layer ridge hangs tough off
the Mid-Atlantic and southeast US coast. The upper ridge has been
been anomalously strong of late with the western periphery of the
H50 ridge over the forecast area today (~5880 meters) being some
50 meters above the climatic daily max for this date. The strength
of the ridge and the position of a synoptic scale surface high to
our east has resulted in several high temperature records, either
tied or broken over the past several days, including today. In
fact, worth noting, if the low temperature from last night of 71
degrees holds at Mobile, this would smash the warmest low on
record by 4 degrees. This would also be 5 degrees above the
normal high temperature for this date. For Pensacola, if the low
temperature from last night of 70 degrees holds, this would
surpass the previous warmest low on record by 2 degrees. Same as
with Mobile, this would also stand at 5 degrees above the normal
high temperature for this date.

Very little change in the near term forecast philosophy, with a
persistence type approach taken with the upper air and surface
pressure patterns changing little in position. Will maintain a
small chance of showers mainly over the western zones this
evening, rooted in a deep, moist southerly flow. High risk of
dangerous to potentially deadly rip currents continues along the
Florida Gulf coast into tonight due to long period swell (7 to 8
seconds) impinging along area beaches and moderate onshore flow.
Indications continue to favor the development of coastal fog
tonight which may develop inland thru the night. The high
resolution HRRR and higher probabilities of restrictions in
visibility at less than 3 miles from the latest short range
ensembles are more focused along and southeast of I-65 with the
better fog coverage tonight. Overnight lows remain well above
normal. For Thursday, there are indications that the western edge
of the deep layer ridge may build back west resulting in a
continuation of anomalously strong mid level heights and
potential of record high temperatures being tied or broken at
several locations. /10

SHORT TERM /Thursday night Through Saturday night/...The highly
anomalous strong upper level ridge over the western Atlantic will
continue to nose westward across the Florida peninsula and into
the east central Gulf of Mexico through Friday. A deep layer dry
and subsident airmass will remain in place across our forecast
area through Friday morning, which supports maintaining a dry
forecast Thursday night into Friday morning. Patchy fog formation
will also be possible again late Thursday night into early Friday
morning. A shortwave impulse in the southwesterly mid level flow
pattern northwest of the ridge axis and ahead of the persistent
trough over the western CONUS will lift northeastward across
Louisiana into Mississippi Friday. Associated increased deep layer
moisture and ascent will clip our western zones Friday afternoon
into Friday night, favoring a low chance of showers and perhaps a
few thunderstorms roughly west of a Butler to Gulf Shores line.

Southwest mid level flow will increase across our area Saturday
into Saturday night as the broad upper level trough progresses
eastward into the central Plains states. The associated cold front
will finally get a push eastward into southeast Louisiana and
Mississippi and into southwest Alabama by late Saturday night.
We expect scattered showers and isolated thunderstorms to develop
across much of the area by Saturday afternoon in the warm and
moist environment ahead of the approaching front. Deep layer
moisture and ascent will increase over our northwestern CWA
along the frontal zone Saturday night, and have POPs becoming
likely over interior southeast Mississippi and southwest Alabama,
with a chance across the remainder of the region. MLCAPE may
approach 300-700 J/KG Saturday afternoon, decreasing somewhat by
Saturday evening. 35-40 knots of 850 mb flow may also clip our
northwestern zones Saturday afternoon and evening, where we may
have to monitor for a few strong to marginally severe storms.
Otherwise, little change in temperatures is expected through
Saturday night, with potential for more record warmth Friday
through Saturday. /21

LONG TERM /Sunday Through Wednesday/...The frontal boundary will
become oriented near the coast during the day Sunday before
pushing offshore Sunday night into Monday. Medium range guidance
continues to show deep moisture and ascent spreading over this
boundary Sunday into Monday, so have gone with likely POPs through
this period. There could be a potential of locally heavy rain
Sunday night into Monday morning. Moist westerly flow holds into
the middle of next week. Will maintain a chance of POPs during the
Monday night through Wednesday period. Slightly cooler temperatures
also return behind the front during the extended period. /21

MARINE...Main hazard in the near term would be patchy fog
developing near bays and sounds. /10


FL...High Rip Current Risk until 3 AM CST Thursday for FLZ202-204-206.



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