Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 231140
AFDMOB

Area Forecast Discussion
National Weather Service Mobile AL
640 AM CDT Sat Sep 23 2017

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

&&

.AVIATION...
23/12Z issuance...Clear skies and VFR conditions start off the
forecast, with a few areas of patchy MVFR to IFR fog early this
morning, dissipating shortly after sunrise. Isolated to scattered
SHRA/TSRA are expected to develop again this afternoon. Much of
this activity will be over inland areas away from the coast, so
confidence on impact at KMOB/KBFM/KPNS remains low, so will not
include more than VCTS in local TAFs. Generally light east to
northeast surface winds expected through the period. 12/DS

&&

.PREV DISCUSSION... /issued 439 AM CDT Sat Sep 23 2017/

NEAR TERM /Now Through Saturday night/...Isolated to scattered
showers and thunderstorms are again expected this afternoon as
weather pattern over the region will be very similar to yesterday.
Some of the storms that developed yesterday afternoon produced
gusty winds up to around 40-45 mph and some small hail up to
around nickle size, and believe that potential will again exist
today. Water vapor imagery indicates that the mid levels of the
atmosphere will be slightly more moist today which could somewhat
limit downdraft potential as compared to yesterday. However,
evening sounding data still shows large area of -10C to near -11C
at 500 mb, upstream of our forecast area. Model data shows these
relatively cold temps aloft will advect into our area today with
the northeasterly flow aloft on the north side of the
aforementioned upper low. With this, rather steep 700mb to 500mb
lapse rates today will be comparable to those of yesterday, around
6.2C/KM to 6.6C/KM. So believe that there is a potential for at
least some small hail with any of the storms that develop today,
and perhaps some strong wind gusts up to around 40 mph as well.
while a few strong storms will be possible, other than an isolated
storm or two, the severe threat is very low. Any lingering
convection will diminish during the early evening hours with the
loss of daytime heating and instability. As has been the case for
the past several nights, there could again be some patchy light
fog tonight, especially for those areas that receive the rainfall
today. Surface high pressure ridging in from the northeast will
continue to maintain a light, predominately east wind flow across
the region today, with a slight southeasterly component near shore
this afternoon in association with the sea breeze circulation.
Highs today 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 over most of the
interior to the low to mid 70s near and along the coast. 12/DS

SHORT TERM /Sunday Through Monday night/...
On Sunday the mid-level low centered over the MS/AL border continues
to gradual move westward. A moist airmass on the eastern side of the
low has PWATs of 1.8 inches which is slightly above the 75%
moving average. Because of the ample amount of moisture associated
with these storms localized heavy rainfall could become
problematic for the southwestern half of the forecast area.
Showers and thunderstorms should begin offshore prior to sunrise
then gradually come onshore in the early morning hours. Over land
storms should linger on until the late evening while offshore the
Gulf will remain warm enough to sustain convection.

Going into Monday morning with the moisture plume still overhead
showers and thunderstorms will remain offshore to start the day.
However any low-level convergence, either from the sea-breeze or
thunderstorm outflow boundaries, should be able to spark convection
overland as well. By the afternoon hours convection should become
more widespread as diurnal heating reaches its maximum. Storms
will subside by the evening hours as the aforementioned low moves
northeast.

Increasing risk of rip currents Sunday and Monday due to the
constant presents of offshore showers and thunderstorms. This along
with a steady easterly flow and a developing long period swell
promotes a moderate risk of rip currents Sunday.

Max temperatures Sunday and Monday should be mitigated by the
showers and storms reaching the mid 80s. Dewpoints remain mostly
unchanged keeping minimum temperatures in the upper 60s. DJ/17

LONG TERM /Tuesday Through Friday/...
Ridge begins to build over the southeast Tuesday due to upper-level
influences from Hurricane Maria. Northerly winds settle over the
northern half of the forecast area and could spark showers along the
coast Tuesday afternoon and evening. Overall however a much drier
profile develops keeping convection to a minimum both Tuesday and
Wednesday.

During the later half of the week a deep trough develops over the
great lakes region and dives south. The corresponding cold front
reaches the Gulf Coast by Friday dropping temperatures into the low
80s/upper 70s to start the weekend. DJ/17

MARINE...
High pressure ridging into the marine area from
the northeast will continue through most of the 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. Flow
increases to near Exercise Caution levels on Sunday as gradient
tightens between the high pressure to the north and Hurricane Maria
making its closest approach to the east coast of Florida. Flow
relaxes once again by Monday as Maria continues to move up the
Atlantic east coast. Seas initially around 2 to 3 feet, increasing
to around 4 feet on Sunday, then decreasing to 2 feet or less 1-2
feet offshore with smooth conditions on protected waters, increasing
to 3 to 4 feet over the weekend, before subsiding once again to
around 2 feet once again during the early part of next week. By
midweek, a weak frontal passage will likely result in a light
northwesterly flow over the marine area. 12/DS

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...None.
FL...None.
MS...None.
GM...None.
&&

$$

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