FXUS64 KMOB 210458 AAC

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1158 PM CDT Tue Aug 20 2019

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


06Z issuance...General MVFR to VFR conditions start the forecast.
As the night progresses, showers and thunderstorms developing
along and south of the coast will move inland overnight, bringing
localized drops to lower end MVFR levels in heavy rain to coastal
areas. Inland from the coast, localized fog development can bring
drops in VISBYs to low end MVFR levels closer to sunrise, but is
expected to quickly mix out after. Afternoon thunderstorm
development is expected, bringing drops in conditions to lower end
MVFR levels and possible impacts to operations. Convection will
decrease in coverage and strength into the evening hours with the
loss of the day`s heating, with general VFR conditions expected
after 03Z. A general southerly flow is expected through the
forecast. /16


.PREV DISCUSSION... /issued 848 PM CDT Tue Aug 20 2019/

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

UPDATE...Overall the afternoon forecast package remains on track.
Just included some patchy fog development tonight to the current
forecast. /08

PREV DISCUSSION... /issued 701 PM CDT Tue Aug 20 2019/

DISCUSSION...Updated for latest aviation discussion below.

00Z issuance...Widely scattered showers and storms linger through
early evening before slowly dissipating. Winds become light and
variable overnight. Patchy light fog is possible by 06Z across
areas that received rain today with visibility dropping to IFR or
LIFR for a short period at the TAF sites near sunrise. Showers
and storms redevelop by late morning. 07/MB

PREV DISCUSSION... /issued 337 PM CDT Tue Aug 20 2019/

NEAR TERM /Now Through Wednesday/...20.12Z upper air analysis
shows a trof axis at multiple levels from the Appalachians
stretching southwest over the central Gulf coast. At the surface,
a weakly defined pressure trof has migrated slowly northward over
the I-65 corridor today where visible satellite imagery animations
and radar loops continue to show a cyclonic motion to
cloud/precipitation elements around the trof axis. Meso-analysis
shows deepest Gulf moisture (PWATs 1.9 to 2.2 inches) along and
southeast of I-65. Scattered to numerous showers and storms have
used up instability with mixed layer CAPE values in areas where it
hasn`t rained ranging 1000-1500 J/KG over the land zones. Storm
cores have had a hard time maturing this afternoon, with over-all
core heights staying below -20C height at ~ 26.2 KFT per RAP BUFR
soundings. Although storm growth has been lacking, deep layer shear
being non-existent and mid level lapse rates ~ 5.5C/KM, forecasters
still cannot rule out a few afternoon perhaps early evening storms
becoming briefly strong. Deep layer environmental moisture supports
some storms being efficient heavy rain producers. Going into the
evening, ensembles of the high resolution models show a rapid
decrease in coverage. Some patchy fog possible late in the night in
those areas that received heavier rains today. Overnight lows mostly
in the lower to mid 70s.

A weak shear axis aloft remains positioned over the southeast
US and central Gulf coast on Wednesday. With deep layer moisture
holding and with onset of daytime instability, scattered to
perhaps numerous showers and storms are expected. Daytime highs
range from 88 to 93. /10

SHORT TERM /Wednesday night Through Friday night/...An unsettled
weather pattern will remain in place through the short term. A
very moist airmass with precipitable water values around 2 inches
combined with an upper level weakness will continue to generate
scattered to locally numerous showers and thunderstorms each day.
Showers and thunderstorms will start near the coast in the
morning and spread inland through the late morning. Convective
coverage will be most numerous over the land areas during peak
daytime heating. The upside to the additional rain and associated
clouds will be temps that will be at or slightly below normal. /13

LONG TERM /Saturday Through Tuesday/...Very little change in the
pattern through the extended range as plenty of deep layer
moisture will continue across the Gulf coast with precipitable
water values over 2 inches. This will continue the pattern of
diurnally driven scattered to locally numerous showers and
thunderstorms each day. /13

MARINE...A light mostly onshore flow continues over the marine
area as a ridge of surface high pressure continues to stretch
from the western Atlantic to the north central Gulf. Winds, waves,
and seas will be locally higher near thunderstorms through the
forecast period. Conditions will also remain favorable for
isolated waterspouts, especially during the morning and early
afternoon hours. /10




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