Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 221134

Area Forecast Discussion
National Weather Service Mobile AL
634 AM CDT Fri Sep 22 2017

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


22/12Z issuance...VFR conditions will generally prevail for the
next 24 hours except for MVFR conditions in patchy light fog
early this morning and then again late tonight. Brief MVFR/IFR
also possible in some locations this afternoon as isolated to
scattered showers and thunderstorms develop, ending shortly after
sunset. Light, primarily easterly surface winds through the
period. 12/DS


.PREV DISCUSSION... /issued 434 AM CDT Fri Sep 22 2017/

NEAR TERM /Now Through Friday night/...Pattern generally
unchanged from yesterday, with an upper level trof axis remaining
just to the east of our forecast today. This trof will likely close
off into a weak upper low over the Gulf just to the east-southeast
of the area tonight. Extending up toward the northwest across the
forecast area, upper ridging continues there, and on up to the
northwest of there. Models indicate that a series of weak shortwaves
will move southwest across the area in the moderate northeasterly
upper flow that is present between the two aforementioned upper
features. These weak upper disturbances, combined with the
moderately moist low level airmass (PWAT`s in the 1.4 to 1.8 inch
range) will provide just enough dynamics to produce isolated to
scattered showers and storms across the area today, especially in
the afternoon with max daytime heating and instability, and
additionally supported by sea breeze interactions near the coast.
Any lingering convection late today will end shortly after sunset
this evening, with little to no pcpn expected overnight. There could
be some patchy light fog tonight, however, especially for areas that
receive the rainfall today. Surface high pressure ridging in from
the northeast will continue to maintain a light east to northeast
wind flow across the region. Warm again today with highs in the
upper 80s and lower 90s over most of the interior, and mid to upper
80s along and near the coast. Lows tonight expected to range from
the upper 60s and lower 70s over most inland areas to the mid 70s at
the immediate coast. 12/DS

SHORT TERM /Saturday Through Sunday night/...
On Saturday a westward moving broad mid-level inverted trough over
the southeast should provide the lift needed to produce scattered
convection from an already moist and unstable atmosphere. Over
our forecast area, CAPE values should be over 1500 J/kg with PWATS
above 1.5 inches. Thus isolated to scatter thunderstorms and
showers should be possible in the afternoon hours with maximum
temperatures in the upper 80s.

Though rain chances overland subside during the evening hours, they
remain relatively high offshore. An offshore plume of 1.7-1.9 inch
PWATS maintains the convection over the marine zones and gradually
comes onshore in the early morning hours on Sunday. With the
additional cloud cover and scattered showers minimum temperatures
should be in the upper 60s overnight.

Sunday is expected to be rainy. Models are in good agreement with
scattered to numerous showers of increasing coverage and intensity
near the Alabama and Mississippi border. Lighter showers expected
elsewhere around the forecast area. Showers should assist in keeping
the maximum temperatures in the mid 80s. Though these showers should
lessen by the late evening hours, the moisture plume remains
overhead making it difficult to determine exactly when the rain
should end. Early Monday morning should again see offshore showers
and thunderstorms. 17/DJ

LONG TERM /Monday Through Thursday/...
The last vestiges of the moisture plume and inverted trough begin to
exit the forecast area Monday though with PWATS about 1.8 inches
still anticipate some showers and possible thunderstorms in the
afternoon hours Monday. Similar to Sunday the highest coverage and
intesity appears to be focused on the western half of the forecast
area. Again showers should keep the high temperatures in the mid 80s.

Tuesday through Thursday sees a mid-level ridge begin to build into
the central Gulf Coast. The ridge helps advect dry air south over
the CWA decreasing the 850-500mb average RH down below 50%. The
resulting clear skies should allow for temperatures to reach the low
90s in the later half of the week though minimum temperatures
remain in the upper 60s. 17/DJ

MARINE...High pressure ridging into the marine area from
the northeast will continue through the entire forecast period, with
a primary light to occasionally moderate easterly wind flow
continuing over the marine area. Still expect a slight offshore
component during the late night and early morning hours and a slight
onshore component during the afternoon and early evening hours. Seas
initially around 1-2 feet offshore with smooth conditions on
protected waters, increasing to 3 to 4 feet over the weekend, before
subsiding to around 2 feet once again during the early part of next
week. Isolated to scattered showers and storms possible over the
marine area through the period. 12/DS




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