Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 160323 AAB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1023 PM CDT Sat Jun 15 2019

.DISCUSSION...See updated information for land areas below.


.UPDATE...Persistent rain/thundershowers over southeast
Mississippi continue to decrease in coverage as the airmass over
the region cools and instability is lost. Increased upper level
cloud cover from the evening`s convection will help to limit
overnight cooling as compared to previous nights. Lows ranging
from around inland to mid 70s along the coast expected. /16


.PREV DISCUSSION... /issued 656 PM CDT Sat Jun 15 2019/

DISCUSSION...Updated for latest aviation discussion below.

00Z issuance...VFR conditions are expected to remain prevalent
through the next 24 hours. Isolated showers and thunderstorms over
interior southeast MS and southwest AL may linger for another
couple of hours before dissipating. Showers and storms may be more
scattered in coverage on Sunday afternoon, especially across
southeast MS and southwest AL. We opted to include VCTS at KMOB
and KBFM after 18Z Sunday. Brief gusty winds, frequent lightning,
locally lower ceilings/vis, and heavy rain will be possible near
stronger storm cells. Otherwise, winds become calm to light
southerly tonight, then south to southwest 5-10 knots (perhaps a
little higher around 12 knots at times near the coast) during the
day Sunday. /21

PREV DISCUSSION... /issued 400 PM CDT Sat Jun 15 2019/

NEAR TERM /Now Through Sunday/...A surface ridge remains in place
over the western Atlantic and eastern Gulf, maintaining a light
onshore flow across the area through the near term. Ongoing showers
and thunderstorms along the western periphery of this ridge will
continue to impact portions of southeast Mississippi and far
southwest Alabama through this evening before tapering off after
sunset as instability wanes. No rain chances carried through tonight
as lows stay in the low 70s inland and mid 70s along the coast.

An upper level shortwave ejects from the southern Rockies eastward
over the South Plains during the day Sunday. Weak divergent flow out
ahead of this wave will overspread the local area and aid in
convective initiation Sunday afternoon. Expecting scattered coverage
over much of the area, perhaps becoming more numerous along outflow
boundaries and the inland-advancing sea breeze as the afternoon
progresses. High temps will reach the low 90s inland and upper 80s
along area beaches. /49

SHORT TERM /Sunday night Through Tuesday night/...The north
central Gulf region is expected to remain on the northwest
periphery of the subtropical high that has been dominating area
weather. Warm and muggy conditions will continue as an onshore low
level wind flow persists. Afternoon convective coverage increases
as minor shortwave troughs moving through the southwest to
westerly flow aloft interact with afternoon instability, a moist
atmosphere, and low level forcing along the sea breeze front as
well as outflow boundaries formed by dissipating thunderstorms
once convection is initiated. As instability decreases late
afternoon and evening, storms will gradually subside and decrease
in coverage. Models project the ridge to be strong enough to keep
stronger dynamics and synoptic forcing west and north of the
forecast area. Hence, the convective regime developing each
afternoon will be one consisting of high instability within a
weakly sheared environment which will favor the development of
short lived pulse thunderstorms. The stronger of these pulse
thunderstorms storms will be capable of producing locally heavy
downpours, frequent cloud to ground lightning, small hail and
potentially, locally damaging wind gusts.

Temperatures are expected to trend near seasonable norms with
daytime highs climbing into the upper 80s to low 90s.  Overnight
lows will generally range in the low to mid 70s with some interior
sites dropping into the upper 60s and locations along the immediate
Gulf coast only falling into the upper 70s to near 80. /08

LONG TERM /Wednesday Through Saturday/...Very little change
expected in the overall pattern and sensible weather over the region
for most of the period. The subtropical ridge continues to shunt
the stronger dynamics and synoptic forcing west and east of the
north central Gulf region. A moist onshore flow continues, and
minor shortwave troughs propagating through the southwest to
westerly flow aloft interact with the underlying instability and
sea breeze front initiating afternoon convection. Pulse
thunderstorms will generally remain the favored convective mode
for most of the long term. However, both the GFS and ECMWF project
a stronger shortwave trough to impact area weather on Thursday.
The GFS solution is the stronger of the two. The GFS forecasts 0-6
km bulk shear magnitudes of 25 to 40 knots versus the ECMWF
values of 20 to 30 knots. Both project unidirectional shear
profiles and Wet Bulb Zero heights above 12000`. Will trend
forecast more toward the ECMWF at this time suspecting the GFS is
underestimating the strength of the subtropical ridge. The
convective mode on Thursday with the current guidance looks to
favor a multi-cellular one...creating the potential for some
strong to even severe thunderstorms with the primary threat being
damaging straight line winds and possibly quarter size hail in the
strongest updrafts. Confidence of this evolving though remains
low at this time and will continue to monitor for some run to run
consistency in future model runs. Otherwise, temperatures from
Wednesday through Saturday will trend near to slightly warmer than
climatological norms. /08

MARINE...High pressure east of the marine area will maintain a light
onshore flow and little change in seas through Tuesday. Onshore flow
increases and seas build Wednesday through the remainder of the week
as the local gradient tightens between high pressure to our
southeast and a surface trough to our northwest. Chances for showers
and thunderstorms continue throughout the period. Expect locally
higher winds and waves in and around storms. /49




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