Dense Fog Advisory 23, NWS Mobile, AL

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
657 AM CDT Tue Sep 28 2021

.NEAR TERM UPDATE /Now Through Wednesday/...Isolated to scattered
rainshowers have formed over area waters and coastal areas this
morning. Direction of movement indicates a significant portion
may be virga. The KMOB VWP shows southerly winds in the lowest 2k'
of the atmosphere, shifting to westerly by 10k', and
northwesterly by 15k'. Am expecting more and more of the showers
to reach the surface through the day, especially west of the
Tombigbee.

Am issuing a short Dense Fog advisory for areas north of I10,
with a rapid drop in reported conditions, along with better
coverage on the Night Fog satellite loop.

No other updates needed at this time.
/16

&&

.AVIATION...
12Z issuance...At 11z, VFR conditions were noted along the I-10
corridor, with MVFR/IFR conditions, mainly CIGs, north. As light
southerly boundary layer winds increase to 5 to 10 knots this
morning, am expecting conditions to increase to mid level MVFR/VFR,
with local drops to low/mid MVFR levels in showers and
thunderstorms. Highest chance is expected to be along and west of
the Tombigbee River. Conditions are expected to decrease again
tonight as fog forms after 06z with the lightening of the winds.
/16

&&

.PREV DISCUSSION... /issued 455 AM CDT Tue Sep 28 2021/

NEAR TERM UPDATE /Now Through Wednesday/...An upper level ridge
shifts to over the Mississippi River, then stalls, with a surface
ridge stretching west over the northern Gulf coast. Best influx
of Gulf moisture continues to be over the Lower Mississippi River
Valley, with guidance advertising precipitable H20 values rising
around 1.5" along the eastern border of the forecast area to
around 2" over southeast Mississippi through the Near Term. The
latest radar loop shows isolated rainshowers have formed over the
north-central Gulf of Mexico overnight. With the best moisture
flux being generally west of the forecast area, a west to east
gradient in PoPs is expected through the Near Term. Guidance has
been and continues to advertise overnight fog development Tuesday
night, generally east of the Tombigbee River, in an area of better
overnight clearing and lighter winds. Currently, there is enough
mid-level cloud streaming east over western portions of the
forecast area to limit fog development to areas east of the
Alabama River tonight.

Looking at the possibility of any strong to severe storms, guidance
is advertising MLCapes rising into the 1500-2000J/kg range outside
of the precipitation areas with DCapes rising into the 800-1000J/kg
range. Where varies, with best chances being along and east of the
Alabama/Mississippi state line. Add in dry layers in the mid and
upper levels over the less moist areas, damaging downbursts are
possible each day. Helping to limit any organized severe is a lack
of upper support.

With increased moisture levels and upper subsidence from the upper
ridge, the Near Term will see temperatures above seasonal norms.
Tonight's lows temperatures in the low to mid 60s will rise into the
upper 60s to around 70 Tuesday night. The rain will bring a west to
east gradient in high temperatures, with mid 80s west of the
Tombigbee River, upper 80s to near 90 east expected each day.

Even with a large tidal range currently, and steady east to
southeast winds through the week, a Low Risk of rip currents is
expected. There is an uptick to Moderate Friday into Saturday as the
steady flow begins to bring increased swell to area beaches. Helping
to limit the increase is a decreasing tidal range the latter half of
the week into the weekend.
/16

SHORT TERM /Wednesday night Through Thursday night/...An omega-
style blocking pattern will still be in place over the CONUS at
the beginning of the forecast period, characterized by a sharply
amplified upper ridge extending from the north central Gulf coast
towards the Great Lakes, located between a deep upper trof over
the New England area to along/just off the East Coast and a broad
upper trof over the western states. This pattern translates very
slowly eastward, with a series of shortwaves moving across the
area. A surface high pressure ridge will continue over the
southeast states, with a persistent southeasterly flow across the
region. This mostly onshore flow will continue to gradually modify
the airmass in place across the area, with moisture slowly
increasing. This increasing moisture, along with daytime heating
will result in scattered convective development on Thursday,
especially over the western half of the forecast area with only
isolated PoPs over the easternmost portions of the area where
subsidence effects associated with the ridging will continue to be
strongest. May see some strong storms develop Thursday afternoon
due to entrainment of some still lingering dry mid level air. Lows
Wednesday night and Thursday night will range from the mid 60s
well inland to around 70 at the coast. Highs on Thursday generally
range from the mid to upper 80s, although a few spots over south
central Alabama may reach the lower 90s. /12

EXTENDED TERM /Friday Through Monday/...For the first half of the
extended period, an upper-level ridge will move into the Southeast
US. Subsidence from this ridge will lower rain chances on Friday
(with the exception of slight PoPs over portions of Southeast MS)
and will remain low through Saturday. By Sunday, upper-level
troughing over the Northern Rockies and Southern Plains will combine
and move eastward, allowing for the ridge to weaken and move off the
Eastern Seaboard. At the surface, guidance is hinting at a low
developing near the Northern Ohio River Valley, with an associated
frontal boundary extending southwestward. As this feature moves
towards the east, south to southwesterly flow out ahead of the
boundary will allow for an increase in moisture and precip heading
into Monday. There is uncertainty in whether or not this boundary
will make it through the area. For now, went with chance PoPs for
our western communities on Monday, gradually decreasing to slight
chance for our eastern communities. If, however, the boundary
becomes stationary over the area, may need to adjust PoPs upward
in future updates.

High temperatures will warm to the upper 80s to lower 90s on Friday
and Saturday while under the influence of the ridge. Highs will
taper off a bit on Sunday and Monday to the low to mid 80s thanks to
an increase in cloud cover and precip chances. Lows throughout the
period will remain in the mid to upper 60s, with lower 70s along the
coast /96

MARINE...A surface ridge stretching west over the northern Gulf coast
will bring a light to occasionally moderate east to southeast flow
through the remainder of the week and into the weekend. Seas generally
2 feet or less expected through mid week, with an slight uptick
in sea heights Friday into the weekend as increased swell moves
over area waters. /16

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...Dense Fog Advisory until 10 AM CDT this morning for ALZ051>060-
     261-262.

FL...Dense Fog Advisory until 10 AM CDT this morning for FLZ201-203-
     205.

MS...Dense Fog Advisory until 10 AM CDT this morning for MSZ067-075-
     076-078-079.

GM...None.
&&

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