Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 141723

Area Forecast Discussion
National Weather Service Mobile AL
1123 AM CST Thu Dec 14 2017

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


18Z issuance...VFR conditions expected through the period. A few
mid level cloud decks will traverse the area on westerly flow.
Generally light southwesterly surface winds will decrease to light
and variable after sunset tonight. A weak cold front will traverse
the area during the late night and early morning hours, causing
winds to become northerly by daybreak Friday. An increase in mid
level clouds can be expected behind this front. 05/RR


PREV DISCUSSION... /issued 430 AM CST Thu Dec 14 2017/

NEAR TERM /Now Through Thursday night/...A potent upper trough
digs south across the Great Plains through the near term,
extending as far southwest as northern Mexico by late tonight.
To the east of this trough, zonal flow continues over the Deep
South and Southeast U.S. At the surface, a ridge of high pressure
builds east from the southern high plains and Texas panhandle into
the lower Mississippi River Valley. This ridge pushes a weak
front south through our area late tonight. The frontal passage
should remain dry due to limited available moisture over land and
the weak nature of the front itself. North winds behind the front
then usher in a cooler airmass to start the short term. /49

SHORT TERM /Friday Through Saturday night/...A cool dry airmass
will filter in from the north on Friday in the wake of the weak
cold front moving south across the northern gulf. A 1025mb surface
high pressure area will build over the southeast states through
noon Saturday, and then lift northeast through Saturday night.
Over-running along the western periphery of the departing high
pressure will bring isolated to low-end light rain or showers to
the far western portions of the forecast area Saturday night.
Rain-free conditions will persist across the remainder of the
forecast area through the short term. /22

LONG TERM /Sunday Through Wednesday/...A strong upper level
trough extending from south central Canada to Baja California will
move east over the Great Plains to the east coast early next week.
The surface high pressure area will continue to move eastward
Sunday and Monday as a series of weak surface troughs pass north
of the area.

Rain coverage will increase from west to east Sunday morning, with
numerous to definite rain showers with embedded thunderstorms
forecast for Sunday afternoon. Scattered to likely rain showers
with embedded thunderstorms will occur Sunday night, followed by
scattered coverage Monday and Monday night.

While the latest ECMWF and GFS model runs still have a low level
jet arriving with this system on Sunday, the speeds have lowered
to between 35 to 45 knots. However, a 120 to 150 upper level jet
is still expected to develop over the eastern conus Sunday night
into Monday, with the forecast area residing in the favorable
right entrance region. The potential for strong to marginally
severe storms Sunday and Monday remains, with the primary threats
being damaging straight line winds and perhaps a few tornadoes.

The precipitation timing mid week between the ECMWF and GFS with
this next system have diverged once again as the GFS has the upper
energy associated with the southern base of trough approaching
the region on Tuesday, while the ECMWF has the upper energy
approaching the region on Wednesday. Went with a blend of coverage
for now. /22

MARINE...Westerly flow diminishes today before a cold front moves
south across the marine area late tonight. A moderate offshore
flow develops in its wake, gradually shifting to more easterly
throughout the day Saturday. Moderate to strong onshore flow sets
up by late Saturday night and lasts through early next week, along
with an increase in rain chances. The next frontal passage occurs
sometime late Tuesday or early Wednesday, with yet another round
of moderate offshore flow in its wake. Seas generally around 1 to
3 feet through Saturday, building to 3 to 6 feet through early
next week with the onset of stronger onshore flow. /49




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