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fxus64 kmob 011831 aab 
afdmob

Area forecast discussion...updated
National Weather Service Mobile Alabama
1231 PM CST Wed Mar 1 2017

Discussion...see updated information for land areas and aviation
discussion below.

&&

Update...an upper shortwave will be passing over the Midwest
states and the Great Lakes region this afternoon and evening, with
the base reaching as far south as the Tennessee River valley. A
deep southwest wind flow will persist south of the shortwave over
the forecast area through early evening, with weak upper level
impulses passing overhead. At the surface, a high pressure ridge
across the eastern Gulf of Mexico will maintain a breezy and moist
southerly wind flow across the region. The cold front currently
extends from central Tennessee to southwest Louisiana, with
numerous showers and scattered thunderstorms occurring along the
front. This cold front will continue to move southeast at a 25 to
30 mph, and will move into the extreme northwest portion of our
forecast area after 4 PM. The numerous showers and scattered
thunderstorms along the front will move fairly quickly through the
forecast area, with the leading edge of the line reaching the
I-65 corridor around 7 PM. This line will decelerate slightly as
it moves through the remainder of the forecast area during the
evening hours, with the precipitation ending across our extreme
southeast zones by 11 PM.

Mesoanalysis of the pre-storm environment ahead of the
approaching line indicates MLCAPE values near 1000 j/kg, effective
bulk shear values of 55 to 60 knots, and 0-3 storm relative
helicity values of 150-250 m2/s2. Therefore, still expect strong
to severe thunderstorms within the line with damaging thunderstorm
wind gusts and large hail the main threats, and isolated brief
tornadoes possible. /22

&&

Aviation...
18z issuance...prevailing MVFR ceilings with bases near 3000 feet
are expected along the northern Gulf region through this afternoon,
although there could be brief scattered cloud coverage at times.
A line of numerous showers and scattered thunderstorms along a
cold front approaching from the northwest will move fairly quickly
through the area this evening. For now added 3 hour tempo groups
to the tafs for this line, but further updates will be made to
better represent the arrival and departure of the precipitation.
IFR ceiling and strong gusty north winds will follow the frontal
passage, with ceilings gradually improving through the overnight
hours. The winds however will remain out of the north through the
reaminder of the forecast, with frequent gusts to 30 knots. /22

&&

Previous discussion... /issued 623 am CST Wed Mar 1 2017/

Discussion...updated for latest aviation discussion below.

Aviation...
12z issuance...MVFR to IFR cigs and visibilities through about
01.15z followed by MVFR to VFR cigs through about 02.09z followed
by mostly VFR conditions through 02.12z. Lower cigs and
visibilities due to low clouds and fog this morning followed by
low clouds and visibilities mostly in and around showers and
thunderstorms this afternoon and this evening. Winds will be south
at 10 to 15 knots with gusts to 20 knots today and this evening
shifting north in the wake of a strong cold front after 02.06z.
32/ee

Previous discussion... /issued 445 am CST Wed Mar 1 2017/

Near term /now through Wednesday night/...a broad mid to upper
trof over the Central Plains states this morning will shift just
east of the MS River Valley by 12z Thu allowing a surface cold
front to move eastward reaching the central Gulf states and
western sections of the forecast area by early this evening then
east of the forecast area by after 06z Thu. Ahead of this trof a
well defined 50kt h8 jet stretched from East Texas and much of la to
the Tennessee/Ohio River valleys by 12z this morning progged to lift east-northeast
passing mostly north of the forecast area through 00z Thu. The
best shear...mostly unidirectional...looks to approach from the
west early this morning passing mostly over western and northern
sections of the forecast area through 18z today then lifting to
the north by mid to late afternoon. The better low level dynamics
or 850 jet looks to be in phase with the better instability around
midday then lifting off to the north and east during the
afternoon suggesting the best chance for severe weather looks to
be during the early to mid afternoon occurring mostly over western
and northern sections of the forecast area...then followed by a
weaker second round over eastern sections of the forecast area by
late afternoon and early evening. With the weakening trend during
the afternoon hours the storm predication center in Norman OK has
now lowered the severe threat from slight to marginal which
affects mostly inland areas generally along and north of the I-10
corridor. With the limited vertical shear and sfc based CAPES
around 750 j/kg kg damaging straight line winds...large hail and
isolated tornadoes will be the main threats. Skies will be mostly
cloudy today helping to keep afternoon temps mostly in the upper
70s to near 80 followed by clearing skies tonight with lows in the
mid to upper 40s mainly over extreme northern sections of the
forecast area and the lower to middle 50s for all other areas to
the south. 32/ee

Short term /Thursday through Friday night/...an upper trof over
the eastern states slowly moves off into the western Atlantic
with a large surface high building from the plains into the
eastern states. Dry conditions prevail over the area as very dry
deep layer air flows into the region on Thursday in the wake of
the earlier cold front and persists through Friday night. Highs
on Thursday will be in the lower/mid 60s with mid/upper 60s for
Friday. Lows Thursday night and Friday night range from the mid
30s well inland to the lower 40s closer to the coast. /29

Long term /Saturday through Tuesday/...a surface high over the
eastern states shifts into the western Atlantic through Sunday,
leaving a surface ridge over the Gulf Coast states and allowing
for a return flow to ensue over the forecast area. The southerly
flow steadily returns Gulf moisture to the region, with a system
passing well to the north bringing a trailing cold front through
the forecast area late Monday night, although due to timing
uncertainties the passage could be as late as Tuesday night. Will
continue with dry conditions through Saturday night, followed by
a gradual return of mostly slight chance pops through Monday. For
Tuesday will have chance pops west of I-65 with slight chance pops
further to the east. Instability is limited and expect at best
just isolated embedded thunderstorm development. Highs on Saturday
will be mostly in the mid 60s then trend to around 70 for Sunday
with mostly lower 70s for Monday and Tuesday. Lows Saturday night
range from the lower 40s well inland to the lower 50s at the
coast, with warmer lows for Sunday night and Monday night ranging
from the lower/mid 50s inland to near 60 at the coast. /29

Marine...a light to moderate southerly wind flow will continue
through this evening ahead of a strong cold front that moves across
the northern Gulf and marine area by after midnight tonight.
Northerly winds increasing to 20 to 25 knots can be expected in the
wake of the front through midday on Thu then diminishing to around
20 knots through Thu evening...rebuilding to 20 to 25 knots early
Fri morning mostly from cold air drainage from strong high pressure
building from the north. Scattered showers and thunderstorms are
expected ahead and along the cold front late this afternoon and this
evening then shifting south and east of the marine area after
midnight tonight. A few strong thunderstorms will be possible during
this timeframe. Later in the period a moderate to strong easterly
flow persists Fri through much of the weekend as a strong surface
ridge of high pressure shifts east to the eastern Seaboard and
western Atlantic. Small craft advisories are now in effect from
midnight Wed night through 12z Fri morning. 32/ee

&&

Mob watches/warnings/advisories...
Alabama...none.
Florida...none.
MS...none.
GM...Small Craft Advisory from midnight tonight to 8 am CST Friday
for gmz631-632-650-655-670-675.

Small Craft Advisory from midnight tonight to noon CST Thursday
for gmz630-633>635.

&&

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