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FXUS64 KMOB 090535

Area Forecast Discussion
National Weather Service Mobile AL
1135 PM CST Sun Dec 8 2019

.DISCUSSION...See updated information for land areas and aviation
discussion below.


.UPDATE...Areas of dense fog are forming across coastal southwest
AL and soon likely into southern portions of southeast MS. We have
issued a Dense Fog Advisory until 8 AM CST for Stone, George,
Mobile and Baldwin counties, but later shifts will need to monitor
observations farther inland closely for needed expansion. /21 


06Z issuance...A low level trough moving north-northeast over the
forecast area will bring an eastward shifting band of rain over 
eastern portions of the forecast area, with moist east to 
southeasterly low level flow near Mobile Bay and points west along
with eastern Mississippi. For coastal Alabama and inland 
southeast Mississippi, LIFR conditions with east to southeast flow
5 to 10 knots are expected through the night, before rising to 
low end MVFR around sunrise. East of coastal Alabama, a more 
general southerly flow of 5 to 10 knots will bring low end MVFR to
IFR level conditions rising to VFR as one moves northeast along 
I-65. Scattered rainshowers will continue to shift east, and are 
expected to remain light enough to not impact operations.

After sunrise Monday morning, conditions are expected to rise to
VFR forecast area-wide by 15z and last through the day, under a 
general southerly flow around 10 knots. Into Monday evening, 
southerly flow will drop to around 5 knots, with CIGs and VISBYs 
dropping to low end MVFR or IFR by 06z, especially along the I-10 
corridor. /16 


.PREV DISCUSSION... /issued 959 PM CST Sun Dec 8 2019/ 

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

UPDATE...Local web cameras, visibility sensors, and a recent
report from a NWS employee indicate that areas of fog reducing 
the visibility to around 1/4 mile have developed across Mobile 
Bay and most likely the Mississippi Sound. We have issued a Dense 
Fog Advisory for both of these marine zones effective until 6 AM 
Monday morning. This advisory includes the Mobile Bay Causeway and
I-10 Bayway. 

Visibility is also starting to drop across some locations near 
the southwest Alabama coast, including 1.25 miles as of this 
writing at Mobile Regional Airport. SREF probabilities of 
visibility less than 1 mile overnight are highest in a corridor 
from portions of southeast MS through Mobile and Baldwin Counties
and we will be monitoring visibility trends closely for potential
Dense Fog Advisory issuance over these areas. /21 

PREV DISCUSSION... /issued 815 PM CST Sun Dec 8 2019/ 

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

UPDATE...Another update was just sent to the forecast to increase
POPs to likely (~60-70%) chance across a small portion of the 
northwest FL panhandle through the remainder of the evening as a
narrow but steady band of rain showers continues to lift north
toward portions of Escambia and Santa Rosa Counties over the next
few hours. This band should eventually shift east after 11 PM- 
midnight, and continued the trend of lower POPs late tonight over 
our eastern zones. Will continue to monitor radar trends. /21

PREV DISCUSSION... /issued 608 PM CST Sun Dec 8 2019/ 

DISCUSSION...See updated information for marine areas and aviation
discussion below.

MARINE UPDATE...A weak area of surface low pressure is located
off the LA/MS coast this evening, with an associated weak frontal
boundary extending eastward from this feature across the far 
northern Gulf. Winds are subsequently a little more backed to the 
east to northeast along bays and sounds west of Pensacola, with a 
slightly stronger east to southeast flow noted in marine 
observations along marine zones from Pensacola to the Okaloosa- 
Walton County line. We have updated wind grids to reflect these 
trends through the early evening hours, with Small Craft Exercise 
Caution headlines mainly focused over the waters from Pensacola FL
to Okaloosa-Walton County Line FL out 60 NM this evening. Winds 
should gradually decrease and transition more south to southwest 
by late this evening as the surface low pressure moves east and 
weakens. A narrow band of rain showers has been moving from south
to north across the Gulf from near Pensacola to about 60 nm south
of Pensacola for the past few hours. These showers will be capable
of producing reduced visibility from locally heavy rainfall and
perhaps brief gusty winds.  

Conditions will gradually become favorable for fog development 
near bays/sounds later this evening into late tonight. The current
forecast does have mention of patchy dense fog over these marine 
zones late, which looks good. We will be monitoring visibility
trends closely. /21

00Z issuance...Across the forecast area at 23z, IFR CIGs to low end 
MVFR CIGs with VFR VISBYs were noted along and south I-10, rising to 
general VFR conditions well north of I-10. Light rain was streaming 
inland from the Gulf over portions of coastal Alabama and the 
western Florida Panhandle, but remains generally light enough to 
limit any effects to current conditions.

This evening, am expecting the rain to last to around 06Z, then 
taper off, with little change in general conditions. Guidance is 
strongly indicating fog forming after 06z, dropping VISBYs to IFR or 
lower and lasting through sunrise before beginning to rise. Winds 
from the east around 5 knots or less are expected overnight through 
sunrise. Conditions are expected to rise to general VFR during the 
morning hours and remain so through the day, as winds become more 
southerly and increase to around 10 knots. /16 

PREV DISCUSSION... /issued 355 PM CST Sun Dec 8 2019/ 

NEAR TERM /Now Through Monday/...An upper level shortwave is 
currently making its way over the southeastern CONUS and will 
progress over the east coast by tomorrow morning. At the surface, a 
stalled front is currently draped over the northern Gulf coast 
through north-central Florida and off the east coast into the 
Atlantic. This has led to some light shower activity inland and 
along the coast, with some heavier showers over the Gulf waters this 
afternoon. Expecting showers to continue to progress northward, 
eventually tapering off from west to east during the overnight as 
the surface front and upper level disturbance progresses out of the 
area. The Hi-Res models are also in agreement with this trend. 
However, the Hi-Res models do show a slight chance of some isolated 
showers moving in from the west Monday evening ahead of an 
approaching cold front as well.

Temperatures through tomorrow will run above the seasonal norm for 
this time of year. Low temperatures overnight into early tomorrow 
morning will be in the lower 50s for interior SW AL and SE MS and in 
the mid to upper 50s for the western portion of our area and along 
the coast. Highs tomorrow will be a bit warmer than they were today, 
with temperatures reaching the lower to mid 70s area-wide due to 
southerly flow bringing in warmer, moist air up from the Gulf. 

Model guidance also suggests the possibility of fog development 
overnight into early tomorrow morning, particularly for areas just 
north of the I-10 corridor and southward. Locally dense fog 
formation is also possible towards dawn. /26

SHORT TERM /Monday night Through Wednesday night/...Rain chances
increase from northwest to southeast Monday night into Tuesday as
a cold front approaches the area. Fog development is also likely,
particularly closer to the coast where it could be dense at times. 
Widespread showers and storms are expected along and behind the 
front as it passes through Tuesday morning/afternoon, pushing 
offshore by late Tuesday evening. No severe threat expected with 
this front given modest instability, linear forcing, and weak low-
level jet (~30 knots at 850 mb). However, with upper divergence 
improving ahead of the advancing trough and strong ascent along 
the front itself, could still get a few thunderstorms embedded 
within the shower activity, so left slight chance for thunder in 
the forecast. Temps cool down in the wake of the front as north 
winds usher in a more stable airmass. The parent upper trough lags
the surface front, with its primary axis passing over the local 
area during the day Wednesday. Thus, expecting cloud cover and 
showers to linger through the remainder of the short term period 
in the wake of the front. /49

LONG TERM /Thursday Through Sunday/...Another upper trough digs
across the central CONUS right on the heels of the Tuesday 
system, supporting shower activity straight through the remainder
of the week. We remain firmly entrenched within a cool and stable
airmass below 925 mb. However, with south to southwest flow and WAA
setting up in the 925-850 mb layer, could be a classic setup for 
some weak elevated instability to develop above the 925 mb
inversion. Thus, can't rule out a few rumbles of thunder mixed in
with showers during this time. Meanwhile, surface low forms 
beneath the advancing trough Friday into Saturday as it digs into
the Deep South. Right now, majority of guidance suggests this low
forms over the Gulf and lifts northeast, remaining to our south
and east and therefore leaving us under a "cold rain" pattern.
However, it should be noted that some of the more aggressive 
solutions continue to suggest a more potent shortwave gaining a 
negative tilt as it approaches, and thus a much deeper surface low
forming farther west over the north-central Gulf. This would
change local impacts, so will need to continue closely monitoring
this system throughout the week. /49

MARINE...Southeast winds will continue to decrease, becoming 
light into tonight. Winds will become more southerly by Monday 
afternoon ahead of an approaching cold front. An increasing 
offshore flow will then develop with frontal passage late Tuesday,
and will persist through early Thursday in its wake. Thus, a 
Small Craft Advisory will likely be necessary by Tuesday night 
through at least Thursday morning, especially over the Gulf 
waters. Light to moderate northerly flow will follow for late 
week. /26


AL...High Rip Current Risk through late Tuesday night for ALZ265-266.

     Dense Fog Advisory until 8 AM CST Monday for ALZ261>266.

FL...High Rip Current Risk through late Tuesday night for FLZ202-204-

MS...Dense Fog Advisory until 8 AM CST Monday for MSZ078-079.

GM...Dense Fog Advisory until 8 AM CST Monday for GMZ630>632.


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