Special Marine Warning 370, NWS Mobile, AL

Area Forecast Discussion
National Weather Service Mobile AL
648 AM CDT Sun Sep 19 2021

.NEAR TERM UPDATE /Now Through Monday/...A weak upper level low
centered over the ARLATEX region will lift north-northeastward
through Sunday evening, becoming centered over western Illinois by
midnight. However, the base of the upper shortwave that housed
the departing low will remain as far south as the northwest Gulf
of Mexico. This shortwave will eventually become broader and
weaker through the remainder of the near term as it moves very
slowly eastward over the lower Mississippi River region, and a
longwave trough digs southeast over the Northern Plains. PWATs
will remain from 1.9 to 2.2" through Sunday evening, and then
gradually lower from west to east to between 1.7 to 1.9" late
Sunday night through Monday afternoon.

The high initial values will result in a 70-80% of showers and
thunderstorms again today as we maintain a typical diurnal cycle,
followed by isolated to scattered showers and storms Sunday night.
The slightly lower atmospheric moisture on Monday will result in
slightly lower precipitation chances, with a 40-50% of showers and
thunderstorms across the southwest half of the forecast area, and a
60-70% of showers and thunderstorms across the northeast half.
Despite the fact that the Flash Flood Watch was allowed to expire
this evening, isolated instances of heavy rainfall and nuisance
flooding will remain through the near term, especially with any slow
moving showers and storms given the saturated soils. A couple storms
may have some gusty winds thanks to water loading processes.

Low temperatures tonight remain on track to bottom out in the lower
to middle 70's. The same is expected Sunday night. High temperatures
in the lower to middle 80s are forecast both today and Monday.
However, a few readings in the upper 80s could occur Monday
afternoon across south central Alabama. /22 BB/03

&&

.AVIATION...
12Z issuance...A mixed bag of ceilings and visbys across the area
with mostly MVFR and IFR cigs and visbys. Fully expect IFR cigs to
slowly lift throughout the morning with MVFR prevailing throughout
most of the day. Scattered showers and thunderstorms will develop
again by mid-day near the coast then move inland throughout the
afternoon. IFR visbys will be possible within the strongest of
storms during the afternoon. Winds will remain light out of the
southeast becoming light and variable overnight. Storms should
subside during the early evening hours; however, there should be
enough moisture around for another round of lower cigs during the
overnight hours tonight. BB/03

&&

.PREV DISCUSSION... /issued 432 AM CDT Sun Sep 19 2021/

NEAR TERM UPDATE /Now Through Monday/...A weak upper level low
centered over the ARLATEX region will lift north-northeastward
through Sunday evening, becoming centered over western Illinois by
midnight. However, the base of the upper shortwave that housed
the departing low will remain as far south as the northwest Gulf
of Mexico. This shortwave will eventually become broader and
weaker through the remainder of the near term as it moves very
slowly eastward over the lower Mississippi River region, and a
longwave trough digs southeast over the Northern Plains. PWATs
will remain from 1.9 to 2.2" through Sunday evening, and then
gradually lower from west to east to between 1.7 to 1.9" late
Sunday night through Monday afternoon.

The high initial values will result in a 70-80% of showers and
thunderstorms again today as we maintain a typical diurnal cycle,
followed by isolated to scattered showers and storms Sunday night.
The slightly lower atmospheric moisture on Monday will result in
slightly lower precipitation chances, with a 40-50% of showers and
thunderstorms across the southwest half of the forecast area, and a
60-70% of showers and thunderstorms across the northeast half.
Despite the fact that the Flash Flood Watch was allowed to expire
this evening, isolated instances of heavy rainfall and nuisance
flooding will remain through the near term, especially with any slow
moving showers and storms given the saturated soils. A couple storms
may have some gusty winds thanks to water loading processes.

Low temperatures tonight remain on track to bottom out in the lower
to middle 70's. The same is expected Sunday night. High temperatures
in the lower to middle 80s are forecast both today and Monday.
However, a few readings in the upper 80s could occur Monday
afternoon across south central Alabama. /22 BB/03

SHORT TERM /Monday night Through Tuesday night/...An upper trough
will move from the northern plains into the Ohio Valley by
Tuesday night. An associated sfc cold front will will advance into
the southeast ahead of the upper trough Tuesday into Tuesday night.
The airmass over the area will remain very moist with
precipitable water values around 2 inches. The combination of deep
layer moisture, daytime heating and the approaching front will
bring scattered to numerous showers and thunderstorms to the area
on Tuesday continuing into Tuesday night as the cold front begins
to move across the area. Highs on Tuesday will be in the mid 80s
with lows on Tuesday night dependent on where the front is
located, with mid/upper 60s across far northwest areas to low to
mid 70s along the coast. /13

EXTENDED TERM /Wednesday Through Saturday/...An upper level shortwave
trough moving over the Mississippi River continues to move east,
leaving a mean upper trough over the eastern Conus in its wake.
Several shortwave systems move through the mean upper trough through
the Extended, eventually shifting the northern end of the mean
trough east, but leaving the southern end over the Southeast. A cold
front moves south across the southeast Wednesday through Wednesday
night in response to the first passing upper trough, with surface
high pressure settling over the eastern Conus for the latter half of
the week into the weekend. The ECMWF is advertising a deeper upper
trough passing, leading to a stronger cold front and a bit cooler
forecast through the Extended. Guidance does agree in any
precipitation moving south of the coast late Wednesday/Wednesday
evening. So, for the forecast, have showers and thunderstorms in the
forecast for Wednesday, shifting south of the coast Wednesday night.
Have blended the GFS/ECWMF numbers, with temperatures below seasonal
norms expected Wednesday into Thursday, then moderating to around
seasonal by Saturday. Low 50s to low 60s Wednesday and Thursday
nights rise to the upper 50s to mid 60s by Saturday night. High
temperatures in the mid 70s to low 80s Wednesday and Thursday rise
to the low to mid 80s by Saturday. /16

MARINE...A light easterly flow tonight into Sunday morning will
shift to a light to moderate southerly flow through Monday, and then
westerly on Tuesday. Shower and thunderstorm chances and seas 1 to 2
feet will remain possible through Tuesday night. A cold front is
expected late Tuesday night, brining increasing offshore winds and
building seas through midweek. Current guidance continues to suggest
that the end of the work week may have to be watched for a potential
small craft advisory. BB/03

&&

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

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