Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 160532 AAC

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1132 PM CST Fri Dec 15 2017

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


06Z issuance...VFR conditions continue through the period with
predominately light northerly winds becoming easterly on Saturday.


.PREV DISCUSSION... /issued 1039 PM CST Fri Dec 15 2017/

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

UPDATE...Have updated to lower overnight lows a few degrees over
interior areas. Made adjustments to sky cover as interior areas
are clear to mostly clear while thin upper cloudiness lingers over
the remainder of the area.  Made other minor adjustments. /29

PREV DISCUSSION... /issued 505 PM CST Fri Dec 15 2017/

DISCUSSION...Updated for latest aviation discussion below.

00Z issuance...VFR conditions continue for the next 24 hours with
light northerly winds becoming easterly on Saturday. /29

PREV DISCUSSION... /issued 342 PM CST Fri Dec 15 2017/

NEAR TERM /Now Through Saturday/...Upper air map analysis show
complex trof axis aligned from the Great Lakes, southward over
the Mississippi Valley, then southwest across the Red River Valley
of Texas/Oklahoma to the southern reaches of the Gulf of California.
East of this feature, forecasters continue to see east Pacific
moisture being tapped with a large area of clouds streaming
northeast over the deep south. Surface cold front has settled into
the central Gulf with high pressure over Texas beginning to
expand eastward into the deep south. Very little change in the
forecast upper level geo-potential height fields tonight which
should maintain a modest percentage of opaque mid to high based
cloud cover into tonight. The degree of cloud thickness though may
lower somewhat as band of strong upper level westerlies over the
southeast US begins to lift out through the night. Have decided to
go a few degrees above guidance on overnight lows out of respect
for clouds which removes radiational cooling component. During
the day Saturday, the southwest portion of the upper trof axis
over the Gulf of California begins to open up and lift northeast.
Even so, the high level flow remains from a southwest direction
which keeps potential of clouds in place, mixing in with sun at
times. Surface high pressure slips into the southeast US Saturday
which favors a gradual moderation in daytime highs as winds
become more southeasterly in direction by later in the day. /10

SHORT TERM /Saturday night Through Monday night/...
Surface high pressure moves off the southeastern sea board
leading to the development of a southeasterly surface windflow.
Winds aloft back to the southwest as the deep upstream trough
slowly propagates eastward and a warm frontal boundary pushes
northward from the Gulf of Mexico and into the forecast area
Sunday afternoon. As a result, a warm and wet pattern sets
up across the region with precipitable water amounts climbing
as high as two inches over coastal counties. Strong warm advection
will provide enough isentropic ascent to produce widespread rain.
Upper level dynamics provided by minor shortwave troughs moving
through the very moist upper level flow should be enough to
generate some embedded showers from time to time. The potential
exists for 1 to 2 inches of rainfall from Sunday through Monday
night. Widespread fog development is also likely especially near
the coast Sunday night and Monday night as very warm, moist air
advects over our much cooler coastal waters. Temperatures during
this time will trend well above climatological norms. /08

LONG TERM /Tuesday Through Friday/...Models are again divergent
on the long term solution. The GFS is advertising enough upper
level support to push a cold front across the forecast area
Tuesday afternoon through Tuesday evening. However, the ECMWF is
not as progressive with the low pressure system to our west and
keeps us in the wet...soupy pattern through Thursday. Trended
forecast more towards GFS as ECMWF seems to be overly deepening
upper levels waves off the U.S. southwest coast which in-turn
leads to a slower eastern progression. Temperatures expected to
trend near normal Wednesday and Wednesday night but warmer than
normal as a southeasterly windflow develops in advance of the next
approaching cold front. /08

MARINE...By Saturday night as a warm, moist, onshore flow evolves
atop cooler water temperatures over bays, sounds and near shore
waters, the stage would be set for the development of advective type
fog. A better coverage of widespread and potentially dense fog,
likely limiting visibility to below a mile or less, will likely lead
to an increased probability of hazardous boating impacts Sunday
night through Tuesday morning. /10




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