Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 232320 AAA
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
620 PM CDT Sun Apr 23 2017

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

&&

.AVIATION...
00Z issuance...Upper level storm system over central Tennessee
brings wrap around clouds over the central Gulf coast tonight.
Lowest bases are forecast to be at MVFR levels. Vsby ok. Gusty
northwest winds early, forecast to lower to around 10 knots
shortly after sunset. /10

&&

.PREV DISCUSSION... /issued 314 PM CDT Sun Apr 23 2017/

NEAR TERM /Now Through Monday/...A broad positively tilted mid to
upper low/trof generally located over the mid and lower parts of
the Mississippi river valley will continue to shift east towards
the GA/SC coast through Mon afternoon. Main affects further south
from this pattern is a persistent low to mid level cloud deck
generally on the back side of the upper system shifting south
across much of the lower MS river valley and north central gulf
states tonight and early Mon. With a moderate northwest flow also
occurring at surface, allowing cooler drier air to advect south
across the region, conditions will be on the cool side tonight and
early mon followed by a gradual warming trend beginning late Mon
morning continuing through Mon afternoon, due to less clouds,
dimishing winds and more sunshine.

Surface temps will be running about 2 to 4 degrees below seasonal
averages through Mon afternoon resulting in lows in the upper 40s
to lower 50s for most inland areas and the middle 50s along the
coast, followed by highs mostly in the middle 70s for both inland
and coastal locations Mon afternoon. 32/ee

SHORT TERM /Monday night Through Wednesday night/...An upper low
over Georgia/South Carolina moves off to the northeast through
Tuesday night while an upper trof advances from the western states
into the Plains.  Light northerly surface winds over the forecast
area Monday night switch to a light southerly flow on Tuesday as a
surface ridge shifts eastward across the area.  The southerly flow
continues over the forecast area through Wednesday night as a strong
shortwave within the Plains trof ejects off across the Great Lakes
region, and an associated surface low brings a trailing cold front
to near the lower Mississippi river valley. Precipitable water
values will be near 0.6 inches Monday night through Tuesday night
then increase significantly Wednesday night over the western portion
of the area to near 1.5 inches (150% of normal) tapering to values
near 1.0 inches over the far eastern portion.  Will have dry
conditions continuing through Wednesday, then will have chance pops
over the western fourth of the area Wednesday night with slight
chance pops most of the remaining portion as the weak front nears
the area along with the improving deep layer moisture. Lows Monday
night range from the lower 50s inland to the mid/upper 50s closer to
the coast then trend much warmer through Wednesday night to the mid
60s inland with upper 60s closer to the coast. Highs on Tuesday and
Wednesday will be in the mid 80s inland ranging to the upper 70s at
the coast. /29

LONG TERM /Thursday Through Sunday/...A second system advances from
the western states into the upper trof pattern over the Plains, and
evolves into a sharply amplified trof over the central states by
Sunday.  The weak cold front located near the lower Mississippi
river valley Thursday morning lifts northward into the interior
eastern states through Friday.  Elevated deep layer moisture, with
precipitable water values of 1.5-1.75 inches (150-175% of normal),
shifts eastward across the area on Thursday, after which a region of
anomalously drier deep layer air over the Gulf is drawn into the
forecast area in the persistent deep layer southerly flow.  Cape
values around 2500 J/kg are indicated for Thursday, and while shear
values will be relatively low and wet bulb zero values generally
high due to abundant moisture, these conditions suggest some strong
storms will be possible.  Have continued with chance to good chance
pops for Thursday due to abundant deep layer moisture and modest to
moderate isentropic lift, with mostly dry conditions Thursday night
then dry Friday and Friday night as drier air moves into the region.

A surface low over the Plains, associated with the strengthening
upper trof, meanwhile moves off towards the Great Lakes region
through Sunday, and brings another cold front across the southern
Plains, possibly nearing the lower Mississippi river valley Sunday
night.  Deep layer moisture gradually recovers Saturday into Sunday
ahead of the approaching front, and will have small pops return to
the forecast area for Saturday with chance pops for most of the area
on Sunday. Highs on Thursday will be mostly in the mid 80s except
for near 80 at the coast, with mid to upper 80s for most areas each
remaining day.  Lows Thursday night will be near 70 inland with
lower 70s closer to the coast then lows trend a bit cooler through
Saturday night with upper 60s inland and near 70 closer to the
coast. /29

MARINE...A moderate to strong northerly wind flow is expected
this evening and overnight in response to a strong surface ridge
of high pressure shifting south towards the north central gulf. As
a result a small craft advisory is in effect for the open gulf
waters of Alabama and Northwest Florida out to 60 nm including the
lower end of Mobile Bay and the Mississippi Sound east of
Pascagoula from 7 PM CDT tonight through 7 AM CDT Mon morning.
Northerly winds and seas will begin to diminish generally after
sunrise on Mon and continue through Tue morning then shift mostly
southwest by late Tue afternoon as the ridge of high pressure
continues to shift southeast over the eastern gulf. Southerly
winds and seas will then build throughout the week as high
pressure continues along the eastern seaboard combined with a
broad mid to upper trof and developing cold front approach from
the west. Showers and thunderstorms are expected with this pattern
with the first round occurring Thu followed by another round late
Sat into Sun. 32/ee

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...None.
FL...None.
MS...None.
GM...Small Craft Advisory until 7 AM CDT Monday for GMZ631-632-650-
     655-670-675.

&&

$$

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