Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 270135 AAA

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
835 PM CDT Wed Jul 26 2017

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


00Z issuance...MVFR to IFR cigs and visibilities through 28.00z.
Lower cigs and visibilities mainly in and around isolated to
scattered showers and thunderstorms through 28.00z. Winds will be
west to northwest at 5 to 8 knots early this evening becoming
mostly northwest to north around 5 knots or less overnight and
early Thu, then becoming mostly west at 5 to 8 knots Thu
afternoon through early Thu evening. 32/ee


.PREV DISCUSSION... /issued 406 PM CDT Wed Jul 26 2017/

NEAR TERM /Now Through Thursday/...26.12Z upper air analysis shows
a trof of low pressure positioned over the eastern US while a deep
layer ridge extends from New Mexico, eastward into the Mid-South.
Unusual for this time of year, a deep layer north to northeast flow
is in place over the central Gulf coast between these two large
scale pressure systems. A somewhat drier air-mass has settled over
the interior of the region the past 24 hrs where pwat values have
lowered to between 1.6 and 1.8 inches. Closer to the coast, pwat`s
were closer to 2 inches. Despite the lower pwat values over the
interior, there is enough moisture for weak impulses aloft slipping
southward to work on, combined with afternoon instability to support
the development of isolated to scattered showers and storms. Some of
the afternoon storms could be effective in producing brief strong
wind gusts in excess of 40 mph and frequent lightning. Given latest
radar trends, will carry over a small chance of showers and storms
into the evening before decreasing. May see late night redevelopment
over the coastal waters as upper level shear zone and weak surface
pressure trof slips slowly southward off the coast. Overnight lows
in the mid 70s interior to mid to upper 70s coast.

A similar synoptic scale setup, as seen today, is expected on
Thursday with a small chance of showers and storms mostly confined
to the eastern zones. Heat indices will also be elevated as well.
Highs in the lower to mid 90s coupled with dewpoints in the mid 70s
result in afternoon heat indices lifting to a range of 103 to 107.
Although a few values near 108 are seen in gridded heat index
forecasts, not expecting enough areal coverage for a heat advisory
at this time. /10

SHORT TERM /Thursday night Through Saturday night/...Mean upper
level ridging will continue to stretch eastward across the Lower
Mississippi Valley and across central and southern portions of MS
and AL Thursday night and Friday. Generally dry conditions are
expected Thursday night into Friday morning as a drier and more
subsident airmass extends across our area underneath this
feature. The exception could be an isolated shower or storm near
the immediate coast, but most of this activity should be confined
offshore. Deep layer moisture will begin to increase across
central and northern portions of MS/AL by Friday afternoon as a
frontal zone slowly pushes southward into this vicinity from the
Mid Mississippi and Tennessee Valley regions. A few model guidance
members take the southern edge of the deeper moisture and
associated potential for isolated to scattered showers and storms
into northern portions of our forecast area by Friday afternoon
and will continue to carry 20-30% POPs over the northern half of
the area, with continued dry conditions closer to the coast. Heat
and humidity will otherwise remain the main story Friday, with
highs once again reaching into the lower to mid 90s inland, and
around 90 to the lower 90s coast. Max heat indices once again
mostly range between 100-105, with isolated locations between

An upper level trough will continue to deepen over the Eastern
Seaboard through late Saturday, with the associated trough axis
extending southwestward into the northeastern Gulf of Mexico. The
associated frontal boundary will push southward through our area
Friday night into Saturday, with an increasing chance of showers
and thunderstorms spreading southward over the area through this
time frame. We will have likely POPs by Saturday over most of the
area away from the immediate coast. Will have to monitor for
locally heavy rainfall. Better coverage of showers/storms will
gradually push southward near the coast and offshore waters
Saturday night. Highs Saturday trend a little cooler into the
upper 80s to lower 90s with the front and good chance of rain.
Lows range in the 70s Friday night, and may trend a little cooler
into by Saturday night. /21

LONG TERM /Sunday Through Wednesday/...A drier northwest flow
aloft spreads into the area Sunday and Monday on the back side of
the persistent upper level trough over the Eastern Seaboard and in
the wake of the frontal passage. A lingering chance of showers and
storms may continue over southern areas early Sunday, with drier
conditions possibly Sunday afternoon. Isolated to scattered
coverage of convection may hold over southern and eastern areas
Monday and Tuesday, before a little better chance of showers and
storms returns areawide by Wednesday with perturbations within a
more zonal mid level flow. Temperatures remain close to seasonal
levels through the extended period. /21

MARINE...Surface high pressure holds over the Gulf thru the
remainder of the week with a weak surface pressure trof positioned
over the southeast. Little change in seas thru Friday. The Gulf high
breaks down this weekend as frontal boundary sinks southward over
the coastal waters late Saturday. Westerly winds may pickup a bit
going into Saturday causing a slight build in seas. With the passage
of the boundary, a brief period of offshore flow sets up late
Saturday into Sunday. The front settles south of the coastal waters
early next week and stalls while high pressure builds into the
southeast. This results in more of an easterly wind component on
Monday. Small chances of showers and storms. /10




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