Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 201734 AAC
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1134 AM CST Mon Feb 20 2017

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

&&

.AVIATION...
18Z issuance...VFR conditions forecast the remainder of the
afternoon. Southeast winds generally 10 to 15 kts. North to south
band of clouds from Minnesota to the western Gulf begins to
overspread the central Gulf coast tonight. Lowest cig bases
potentially to LIFR categories overnight with small chance of SHRA
moving into MOB/BFM by around 21.06Z. Patchy fog reforms as well
mid to late evening. /10

&&

.PREV DISCUSSION... /issued 809 AM CST Mon Feb 20 2017/

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

UPDATE...Latest observations indicate a rapid improvement in
visibility and the dense fog advisory has been cancelled. Any
lingering patchy fog mainly near area river valleys will lift
quickly through mid morning. Headlines for fog advisories removed
from public and marine zones. /10

PREV DISCUSSION... /issued 625 AM CST Mon Feb 20 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...
12Z issuance...LIFR to IFR cigs and visibilities through about
20.14z then improving to MVFR cigs and visibilities through about
20.16z followed by VFR conditions through about 21.03z followed by
MVFR to IFR cigs and visibilities through 21.12z. Lower cigs and
visibilities mostly in dense fog and low stratus through mid
morning today. Lower cigs and visibilities will be in fog...low
stratus and rain late this evening through tue morning. Winds will
be east at 5 to 10 knots early today shifting southeast at 8 to
12 knots late this morning through tue morning. 32/ee

PREV DISCUSSION... /issued 611 AM CST Mon Feb 20 2017/

NEAR TERM /Now Through Monday night/...Areas of dense fog will
continue along the coast stretching west and northwest over
interior sections of sw AL and se MS through mid morning. A dense
fog advisory in in effect for these locations through 9 am cst
this morning. Sharp upper ridge of high pressure now located near
the AL/GA border and east FL panhandle will continue to shift east
through tonight in response to a deepening upper low center
moving eastward over TX and the western gulf waters today and
tonight. Ahead of this system widespread showers along with a few
isolated thunderstorms are expected...moving into western parts of
the forecast area late tonight and early tue morning. A weak low
center is also reflected near the surface developing along the ms/la
border late tonight and early tue progged to shift southeast towards
the AL and NWFL through midweek.

For today as the upper ridge departs to the east expect
increasing mid to high clouds moving in from the west by early
this afternoon spreading east across the entire forecast area by
late this afternoon and early tonight. Most of the model guidance
is now showing the onset of precip earlier than anticipated
leading to scattered showers along the with a few isolated
thunderstorms moving over most areas generally along and west of a
line stretching from Mobile to Thomasville in AL after midnight
tonight. With limited surface based instability and marginal lapse
rates in the boundary layer along with a very moist column
setting up the main threat with this pattern will be periods of
very heavy rain possibly leading to some localized nuisance flooding
and gusty winds generally less then 30 knots. As for temps have
opted to lean towards the warmer mos numbers for highs and lows
through tonight mostly due to persistence...with afternoon temps
climbing to the lower 80s for most inland areas and the mid 70s along
the immediate coast. Lows tonight will range from the mid to upper
50s to the east and north and the lower 60s to the west and along the
coast. 32/ee

SHORT TERM /Tuesday Through Wednesday night/...Short range model
guidance has come into better agreement with the evolution of the
upper air pattern Tuesday through Wednesday. A deep upper level
low located in the vicinity of the TX/LA border early Tuesday
morning is expected to slowly translate eastward toward southern
portions of LA/MS through Tuesday afternoon before approaching far
southeast MS/southwest AL and the adjacent northern Gulf of Mexico
late Tuesday night into early Wednesday morning. The GFS and NAM
seem to have caught up with the persistent solution the 00Z ECMWF
has been showing the past couple of days, with a very moist and
diffluent southerly mid level flow continuing to gradually move
across western portions of our forecast area through Tuesday
morning, and eastward over the remainder of the CWA Tuesday
afternoon and evening. Precipitable water values are forecast to
rise to the 1.5" to 1.7" range across our forecast area as the
zone of deep layer moisture/lift slowly moves across our area
ahead of the upper level low. This pattern will result in the
development of numerous to widespread showers as well as the
potential for a few thunderstorms, with coverage increasing from
west to east Tuesday into Tuesday evening. We have increased POPs
to categorical coverage (80-90%) over western portions of the area
Tuesday, with 80% coverage shifting toward the northwest FL
Panhandle/far southwest and south central AL vicinity by Tuesday
evening. The very moist airmass in conjunction with a gradual
eastward progression of the zone of deep lift will result in the
potential for locally heavy rainfall Tuesday. Rainfall amounts
between 1-2" with locally higher amounts are generally forecast
over southeast MS and portions of southwest AL, with amounts
averaging 0.4" to around 1" with locally higher amounts farther
north and east across south central AL and the northwest FL
Panhandle.

The upper level low should continue to progress southeastward into
the northern and central Gulf of Mexico during the day Wednesday,
before gradually approaching southern FL late Wednesday night.
Residual moisture on the northern and eastern fringe of this
feature will result in a continued low chance of rain showers
across our area Wednesday, primarily over the northwest FL
Panhandle and adjacent south central AL, but rainfall amounts
should remain fairly light. We will maintain a dry forecast
Wednesday night as moisture exits east of our region.

Highs Tuesday should range from the lower 70s over western and
northern parts of the forecast area to mid to upper 70s farther
to the east. Highs Wednesday are forecast to continue to range in
the mid to upper 70s. Lows Tuesday and Wednesday nights remain
mild in the mid to upper 50s over interior areas and in the lower
60s near the immediate coast. /21

LONG TERM /Thursday Through Sunday/...Shortwave ridging aloft
will build across our forecast area Thursday and Thursday night
with dry weather anticipated. Southwest flow aloft will increase
again by Friday as an upper level trough sharpens over the Upper
Midwestern states. A cold front will progress southeastward
across our forecast area Friday night as the upper trough ejects
across the Ohio Valley region. Meager moisture and lift ahead of
the approaching front may result in the development of isolated
showers and thunderstorms Friday afternoon and evening, and will
maintain a slight chance of convection around the region. A much
drier zonal flow returns this weekend, before the next approaching
system potentially brings the next chance of convection early next
week. Temperatures Thursday and Friday should once again warm well
above seasonal averages, with readings in the upper 70s to lower
80s. A cooling trend is expected in the wake of the frontal
passage, but highs should still reach into the lower 70s across
much of the region this weekend. /21

MARINE...High pressure will weaken over the north central gulf
through midweek as a deep area of low pressure moves east southeast
generally from east TX to the north central gulf through early wed
morning. Numerous showers along with scattered embedded
thunderstorms will move across the marine area ahead of this system
mostly on tue with periods of very heavy rain...gusty winds mostly
30 knots or less and occasionaly cloud to ground lightning. A light
easterly wind flow early today will be followed by a light to
moderate east southeast wind flow this afternoon...followed by a
moderate to occasional strong southerly flow tue through early wed.
Southerly winds and seas will gradually diminish late wed into thu
as the deep area of low pressure shifts east of the region. 32/ee

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...None.
FL...None.
MS...None.
GM...None.
&&

$$

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