Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 181149

Area Forecast Discussion
National Weather Service Mobile AL
549 AM CST Mon Dec 18 2017

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


12Z issuance...Areas of dense fog and low stratus keeping many at
LIFR and VLIFR conditions early this morning. Scattered showers,
and perhaps a few embedded thunderstorms, move in from the
southwest throughout the morning and afternoon, which should help
to improve some of the fog issues and return visibilities to MVFR
or better, though ceilings remain IFR/LIFR. That said, locations
along the coast will likely be pestered by patchy advection fog
throughout the day. More widespread fog then redevelops across the
area tonight, possibly becoming dense once again. Winds remain
light and variable throughout the period. /49


.PREV DISCUSSION... /issued 451 AM CST Mon Dec 18 2017/

NEAR TERM /Now Through Monday night/...Southwest flow continues
in the mid and upper levels through the near term as we remain
parked between a large upper high centered over Cuba and a cutoff
low over the southwestern U.S. Weak ripples in the mid and upper
southwest flow continue to produce showers and thunderstorms
across the local area as they act on an unseasonably warm and
humid airmass below. Still not expecting severe weather or heavy
rainfall, as instability is severely lacking and largely limited
to areas well offshore. Bigger impact continues to be coastal fog
development due to the warm and moist low-level air overrunning
the cool near shore waters. While this fog will be most widespread
and dense during overnight hours, lingering patchy fog will
remain possible along the immediate coast throughout the day.
Inland fog is also expected to redevelop tonight due to the
abundance of boundary layer moisture, wet ground from recent
rainfall, and calm winds. Another Dense Fog Advisory will need to
be considered late tonight into early Tuesday morning for much of
the area. /49

SHORT TERM /Tuesday Through Wednesday night/...Upper high
pressure area centered over Cuba will remain quasi-stationary as
an upper cutoff low moves slowly eastward across the southern
plains through Tuesday night. The cutoff upper low pressure area
will then evolve into an open wave as it passes over the lower
Mississippi River region early Wednesday morning. This shortwave
will then pass over the southeast conus and western Atlantic along
the northern periphery of the upper high through the remainder of
the short term.

A weak surface high pressure ridge will remain across the
southeast states through Tuesday afternoon, and then weaken and
shift southeast as an area of surface low pressure forming over
east Texas on Tuesday moves east across the lower Mississippi
River region by late Tuesday night. This surface low will then
move across the southeast conus and western Atlantic through the
remainder of the short term. A weak cold front associated with the
surface low will then move south through the forecast area
Wednesday night.

Precipitable water values ranging from 1.1 to 1.5 inches will
increase to 1.5 to 1.8 inches by Wednesday morning ahead of the
shortwave, then drop to one-half inch in the wake of the cold

Precipitation coverage will gradually increase Tuesday and Tuesday
night as the upper low approaches the region. Scattered to
numerous rain showers, along with a few embedded thunderstorms,
will occur Wednesday morning, and then taper off from west to
east throughout the afternoon hours as the upper wave moves east
of the region. Dry conditions will occur Wednesday night in the
wake of the cold front. Widespread rainfall amounts through the
short term are only expected to range from two-tenths to four-
tenths of an inch.

The sea fog will continue to develop through the short term as
surface dewpoints in the mid to upper 60s move northward over the
cool gulf and bay waters. Light southerly winds will allow the sea
fog to advect far inland at times. While the inland areas will
see the fog dissipate during the daytime hours, some of our
coastal zones could see extended periods of dense fog lasting
throughout the daytime hours. /22

LONG TERM /Thursday Through Sunday/...The dry period will
persist through Thursday afternoon as a surface high pressure
ridge rebuilds across the region. Precipitation chances will then
increase once again as a longwave upper trough digs south over
much of North America. Additional widespread rainfall amounts
Thursday through Sunday are expected to range from four-tenths to
seven-tenths of an inch. /22

MARINE...Generally light onshore flow continues through Tuesday
before strengthening to exercise caution levels Tuesday night into
Wednesday. Marine fog will remain a persistent issue as warm and
humid air runs over cold near shore waters. Fog will become dense
at times and conditions will warrant close monitoring for Dense
Fog Advisory issuances. Shower and thunderstorm chances likewise
continue across the marine area through midweek. A frontal passage
then brings west to northwest flow Wednesday night into Thursday
before high pressure builds back into the eastern Gulf and a
moderate onshore flow returns by the weekend. /49


AL...Dense Fog Advisory until 9 AM CST this morning for ALZ051>060-

FL...Dense Fog Advisory until 9 AM CST this morning for FLZ201>206.

MS...Dense Fog Advisory until 9 AM CST this morning for MSZ067-075-

GM...Dense Fog Advisory until 9 AM CST this morning for GMZ630>636-



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