Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 291410 AAB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
910 AM CDT Wed Mar 29 2017

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


.UPDATE...Visibilities across the western Florida Panhandle have
been improving through mid morning with most reporting sites up to
one-half mile or greater. Therefore...the Dense Fog Advisory has
been allowed to expire at 9:00 AM. Updated products have been
sent. /22


.PREV DISCUSSION... /issued 616 AM CDT Wed Mar 29 2017/

DISCUSSION...See updated information for land areas and aviation
discussion below.

UPDATE...A dense fog advisory is now in effect for parts of
Northwest florida until 9 AM CDT this morning. Visibilities
lowering to 1/4 of a mile or less can be expected. 32/ee

12Z issuance...IFR to MVFR cigs and visibilities through about 9
AM CDT this morning followed by MVFR to VFR cigs through about
30.03z followed by MVFR to IFR cigs and visibilities through
about 30.14z. Lower cigs and visibilities mostly in low stratus
and fog. Winds will be mostly southeast to south at 3 to 5 knots
early this morning increasing to 8 to 12 knots with slightly
higher gusts through 30.12z. 32/ee

PREV DISCUSSION... /issued 531 AM CDT Wed Mar 29 2017/

NEAR TERM /Now Through Wednesday night/...Mid to upper ridge axis
near the AL/GA border stretching south over the eastern Gulf will
shift east over the western Atlantic through 12z Thu in response
to deep area of low pressure tracking eastward over the middle
part of the country. At the surface high pressure generally over
the eastern Gulf and SE CONUS will shift east to the eastern
seaboard and western Atlantic late today and tonight as main area
of low pressure to the northwest approaches the Mississippi river
valley from the west. With this pattern expect areas of fog and
low stratus early this morning especially over eastern sections of
the forecast areas north of the coast eroding by mid morning as
better mixing develops in the boundary layer. For later this
morning skies will become partly to mostly sunny through this
afternoon followed by increasing clouds from the west by early
this evening spreading east over much of the forecast area by 12z
Thu. As the area of low pressure begins to interact better with
the ridge to the east surface winds will begin to slowly build and
remain up for most areas through tonight limiting the coverage of
fog by early Thu morning.

As for temps, due to more sun than clouds and continued
subsidence in the boundary layer...especially along and east of
the I-65 corridor through early this afternoon...will continue to
lean towards the warmer mos numbers through this afternoon. Highs
today will climb to the mid 80s for most inland areas to the north
and northwest of KMOB and the mid to upper 80s to the northeast.
With mostly cloudy skies tonight will continue to lean towards the
warmer mos guidance leading to lows in the lower to middle 60s to
the north and west of KMOB including areas along the coast and
the upper 50s to lower 60s to the east and northeast. 32/EE

SHORT TERM /Thursday Through Friday night/...Still looking for a
potential severe weather event for Thursday and Thursday night as
a strong storm system approaching the region from the west moves
across the area. Latest GFS has come into better agreement with
the ECMWF with regard to both timing and intensity of the system
since yesterday at this time. Both indicate an approximate 550MB
50H low initially sitting over eastern Kansas at 12z Thursday
moving east to southern Illinois/Indiana by 12z Friday then
weakening and moving to the mid Atlantic coast by late Friday
night. Associated upper trof initially extending south-southwest
across Oklahoma and through central Texas early Thursday morning
moves east toward our forecast area on Thursday afternoon then
east across the area Thursday evening, with shortwave energy
producing a slightly negative tilt to the trof by Thursday

GFS is still slightly stronger with this system than ECMWF. Both
indicate two shortwave energy maxima, one passing well to the
northwest of the forecast area, and another along the coast and
offshore over the northern Gulf of Mexico. With this, could see
two maxima of convective activity with the passage of the system...
one up to the northwest of our forecast area and another over the
Gulf just to the south, with timing of greatest activity over our
area being Thursday afternoon and evening. While modest severe
weather parameters are still forecast by models to be in place
over the region for a period of time from late morning to mid
afternoon (850MB flow generally around 30 to 35 knots, afternoon
MLCAPE up to around 1500-1600 J/KG, mid level LAPSE RATE in the
6.5-7.5 C/KM range and SFC-3KM STORM RELATIVE HELICITY 150-near
200 M2/S2), there is still uncertainty as a thunderstorm complex
over the Gulf could cut off moisture inflow over areas just inland
from the coast and could therefore limit the severe threat over
our area. We will have to see this pans out, and monitor the next
several model runs. At this time, we are in agreement with the
Storm Prediction Center`s SLIGHT RISK of severe weather over the
western 2/3rds of the forecast area (along and west of a general
Greenville AL to Gulf Shores AL line) with a MARGINAL RISK for
points east. All modes of severe weather (damaging winds, large
hail and isolated tornadoes) possible. A greater risk of severe
weather is anticipated west and north of our forecast area over
central and northern portions of Mississippi and Alabama where
atmospheric dynamics will be stronger.

A surface low pressure area is expected to be over eastern
Kansas Thursday morning also moving eastward, reaching the mid
Atlantic states by late Friday night as well. Associated cold
front approaching the region from the west Thursday evening will
sweep east of the forecast area shortly after midnight with storms
and associated severe threat ending during the early predawn hours

A deep southerly wind flow ahead of the system will continue to
advect increasing moisture northward into the region, with
Precipitable Water values climbing to around 1.65 inches Thursday
afternoon, especially across southern half of the forecast area.
With this storms should be efficient rainfall producers and
locally heavy rainfall is possible Thursday. Widespread 1 to 2
inches likely, especially over southern half of forecast area,
with locally higher amounts possible.

Temperatures remain above normal through the period. Daytime highs
in the upper 70s to lower 80s. Nighttime lows in the upper 50s and
lower 60s Thursday night and in the low to mid 50s Friday night.


LONG TERM /Saturday Through Tuesday/...Dry period expected over
much of the weekend as an upper ridge and surface high pressure
dominate the southeast states. Precipitation chances will increase
once again starting late Sunday as yet another upper level trough
develops to our west and advances east over the southern plains,
with scattered to numerous showers and thunderstorms forecast for
Sunday night through Monday night. At this time it appears there
could again be some strong to possibly severe thunderstorms
associated with this system, along with heavy rainfall. Above
normal temperatures will continue through the long term, but
closer to normal Monday with the more widespread rains expected.

MARINE...A light to moderate southerly wind flow will continue over
the marine area through this morning then begin to build this
afternoon and continue through Thu evening ahead of a deep area of
low pressure and surface cold front moving eastward over the middle
and lower part of the country this morning and overnight. Southerly
winds at 15 to 20 knots can be expected by midday Thu continuing
through Thu evening then shifting west to northwest diminishing to
10 to 15 knots late thu night continuing through Fri afternoon as
the upper system and surface cold front track east of the forecast
area by early Fri morning. With this pattern expect scattered to
numerous showers and thunderstorms to approach from the west late
Thu afternoon and Thu evening moving east of the marine area by
early Fri morning. A few strong to severe thunderstorms will be
possible with this pattern especially by Thu evening. Small craft
should exercise caution Thu afternoon and Thu evening. Southerly
winds redevelop over the weekend building by early next week as
another upper system approaches from the west. 32/EE




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