Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 180432 AAC
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1032 PM CST Tue Jan 17 2017

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

&&

.UPDATE...Have updated the package to include the rest of the fa in
the Dense Fog Advisory. With winds settling and visbys dropping,
these areas will see the dense fog soon.

/16

&&

.PREV DISCUSSION... /issued 958 PM CST Tue Jan 17 2017/

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

UPDATE...Visibilities have dropped over the current advisory area.
Am evaluating on timing of expanding it inland. With some reports
dropping inland, am expecting this to occur soon.

/16

PREV DISCUSSION... /issued 609 PM CST Tue Jan 17 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...
00Z issuance...

IFR Conditions are expected to dominate tonight with instances of
LIFR and VLIFR after midnight. Dense fog is anticipated to form in
our inland and coastal areas after midnight and will remain in place
until well after sunrise. High clouds and westerly winds above 25kft
will move-in in the early morning hours. Surface winds are expected
to remain out of the south for the duration of the forecast period.
17/DJ

PREV DISCUSSION... /issued 408 PM CST Tue Jan 17 2017/

NEAR TERM /Now Through Wednesday/...17.12Z upper air map analysis
shows an amplified deep layer ridge positioned over the northwest
Caribbean and the southern Gulf. To the west and north of this ridge,
a tap of east Pacific moisture is seen in satellite imagery streaming
northeast across northern Mexico into the southeastern US within a
well established high level southwest flow. At the surface, a cold
front was draped from the Ohio River Valley to the upper Texas coast.
As a frontal wave of low pressure lifts northeast across the Great
Lakes, the southwest portion of the front is beginning to stall over
the Texas coast. An assessment of deep layer moisture (pwat values)
east of the frontal zone shows values from near 1 inch over northern
Alabama to around 1.4 inches over the lower Texas coast. From a
climatological perspective, these values are near 180% of normal.
Within this zone, radar shows pop-up isolated showers lifting off to
the northeast at 10 to 15 mph. After sunset, the high resolution
guidance tapers off coverage. Even so, could still be a very isolated
shower passing over any one area and feel a 10% chance will
effectively cover this. The placement of the synoptic scale surface
high to the east and the front to our west favors the development of
night-time fog. The high resolution HRRR, NAM12, RAP and MOS guidance
all show this, with fog forming over the southern zones this evening
and spreading northward over the interior. The short range ensembles
also indicate elevated probabilities (70%+) of fog by midnight over
the southern zones (restrictions to visibility dropping off to 1
mile or less). Considering the convergence amongst all the guidance
leading to higher forecaster confidence, a dense fog advisory will be
issued on the 4 pm package beginning at 8 PM and continuing into
shortly after daybreak Wednesday. Upon monitoring trends this
evening, the advisory may be extended northward.

After fog lifts on Wednesday, a small chance of showers possible
thru the day. As for temperatures, no changes with night-time lows
and daytime highs on Wednesday being well above climatic normals. /10

SHORT TERM /Wednesday night Through Friday night/...Upper ridging
extending from the southeast Gulf of Mexico to the lower Great Lakes
will continue to get pushed to the east as an upper level low
pressure area central plains lifts northward. An upper trough
extending southward from the closed low to northeast Mexico around
noon Thursday will swing northeastward, becoming negatively tilted
as it passes very quickly over the region Thursday night. Upper
ridging will then rebuild over the southeast conus on Friday as the
upper trough continues to move northeast away from the area. Weak
surface high pressure will remain across the region through midweek,
and then move east of the area as a weak surface low forming across
the Arklatex region on Thursday lifts northeast to near Chicago by
late Thursday night. Weak surface high pressure will rebuild across
the forecast area on Friday.

A dry forecast is expected through Wednesday evening, with patchy
fog forming across the forecast area once again. Isolated to
scattered coverage of rain showers will move into the forecast area
northwest of I-65 after midnight, followed by likely to definite
showers and thunderstorms spreading east across the forecast area
throughout the day Thursday as the upper trough swing quickly over
the region. A few strong to marginal severe thunderstorms with gusty
surface winds may accompany the line of storms Thursday afternoon and
evening as a low level jet between 40 to 50 knots passes over the
forecast area. Much of the rain will end from west to east after
midnight, with only isolated rain showers occurring throughout the
day Friday.

High temperatures both Thursday and Friday will continue to be warm,
ranging from 71 to 76 degrees. Low temperatures each night range from
the mid 50s to lower 60s. /22

LONG TERM /Saturday Through Tuesday/...A second upper closed low is
expected to form over north Texas by Saturday evening and move east
over northern Mississippi by midnight Sunday night. An associated
surface low pressure area forming across the Texas Panhandle is
expected to strengthen as it moves east, reaching Tennessee during
the same time frame. This will set up another very wet pattern across
our region, with scattered to numerous showers and a chance of
thunderstorms through the weekend, with widespread rainfall amounts
between 2 to 3 inches. A few strong to marginal severe thunderstorms
with gusty surface winds may accompany the line of storms Saturday
into Sunday as a low level jet between 40 to 50 knots passes over
the forecast area. A cold front approaching from the west on Sunday
will move through the region late Sunday, bringing drier conditions
back into the forecast area on Monday. Much of the rain will end from
west to east after midnight Sunday, with only isolated rain showers
occurring throughout the day Monday followed by dry conditions.
Temperatures will continue to be warm through the weekend, with highs
in the lower 70s and lows in the mid 50s to lower 60s. Cooler
temperatures are forecast for Monday with highs in the mid 50s to
lower 60s. /22

MARINE...Main hazard in the near term is areas of dense fog likely
over area bays and sounds tonight bringing restrictions to visibility
to a mile or less. Dense fog advisories in effect for this potential.
High pressure over the Appalachians thru mid week breaks down by
Thursday as a cold front approaches and makes passage across the
coastal waters. A stronger cold front makes passage late on Sunday.
These fronts bring an increased coverage of showers and storms to the
coastal waters. A strong southwest to west flow, choppy to rough
conditions on bays/sounds and high seas forecast late in the weekend
following the passage of the strong weekend front. /10

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...Dense Fog Advisory until 8 AM CST Wednesday for ALZ051>058-060.

     Dense Fog Advisory until 8 AM CST Wednesday for ALZ059-261>266.

FL...Dense Fog Advisory until 8 AM CST Wednesday for FLZ201>206.

MS...Dense Fog Advisory until 8 AM CST Wednesday for MSZ067-075-076.

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

GM...Dense Fog Advisory until 8 AM CST Wednesday for GMZ630>635.

&&

$$

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