Areal Flood Advisory 282, NWS Mobile, AL

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
604 PM CDT Wed Oct 20 2021

.AVIATION...
00Z issuance...Showers, with a few possible embedded storms, will
be possible mainly this evening then again late tonight with a
brief lull in activity in between. Some showers and storms are
expected through the day on Thursday as well. MVFR conditions will
be possible with the heavier showers and storms. An IFR to LIFR
ceiling along with patchy fog is expected to develop over interior
southeast Mississippi and interior southwest Alabama overnight
which then improves to VFR conditions by midday Thursday. VFR
conditions are otherwise expected. South to southeast winds of 5
to 10 knots become light this evening, then a southerly flow of 5
to 10 knots follows for Thursday. /29

&&

.PREV DISCUSSION... /issued 406 PM CDT Wed Oct 20 2021/

NEAR TERM UPDATE /Now Through Thursday/...The mid level flow
pattern has transitioned more W-SW across our region this
afternoon as ridging aloft has moved to our east and a shortwave
impulse is crossing into portions of MS. A plume of deep layer
moisture with increased precipitable water values between 1.6 and
1.9 inches is advecting into our southeast MS and southwest AL
counties, as well as across a portion of the western FL panhandle
this afternoon. Increased ascent ahead of the shortwave impulses
along with some low level moisture convergence has resulted in the
development of scattered to numerous showers along with a few
thunderstorms this afternoon across this portion of our region. A
few of the stronger storms will be capable of producing locally
heavy rainfall this afternoon.

Weak shortwave troughing embedded within a persistent mainly
zonal flow pattern aloft will remain in place across our forecast
area tonight into Thursday. The plume of enhanced deep layer
moisture will slowly advance eastward across our area late tonight
into Thursday morning. This moisture in combination with weak
ascent associated with the shortwave trough axis will maintain a
good chance of showers and a few thunderstorms across our region
tonight into Thursday morning. We will maintain chance to likely
POPs (40-70%) into Thursday morning, with slightly lower POPs
between 30-40% across most places by Thursday afternoon. Lows
tonight will range in the mid to upper 60s inland and in the lower
70s near the immediate coast. Highs Thursday will range in the
upper 70s to lower 80s.

Persistent E-SE flow has resulted in increased swell/surf along
our local beaches and area lifeguards are reporting moderate to
strong rip currents. We have issued a HIGH rip current risk along
the AL/western FL panhandle beaches, effective through tonight. /21

SHORT TERM /Thursday night Through Saturday night/...Broad upper
level troughing encompasses the eastern half of the CONUS Thursday
night into Friday before upper level ridging begins to shift east
and build in Friday night through Saturday night. At the surface, a
cold front slowly sags its way south into the CWA from the north
Thursday night into Friday morning, likely stalling somewhere along
or just north of I-10 for the day Friday as a surface high quickly
forms/traverses the area from west to east Friday into Saturday.

Upper level support moves out quickly Thursday night into Friday
with general subsidence in the mid to upper levels beginning in the
wake of a weak shortwave that traversed the area Thursday afternoon.
This combined with dry air advecting in aloft will help to cut off
any precipitation chances for the short term barring an isolated
shower/thunderstorm Thursday evening along and ahead of the cold
front. Our cold front stalls Friday afternoon along or somewhere
just north of the I-10 corridor, and will serve as a boundary
between low to mid 60's dew points south, and low to mid 50's
dewpoints north. This modulates Friday night into Saturday as the
aforementioned surface high shifts east, allowing for low level
southerlies to take precedence across the area bringing low to mid
60's dew points to everyone in the area. With subsidence aloft and
surface high pressure in control of the area, no precipitation is
forecast Friday through Saturday night across the CWA. Temperatures
will be in the upper 70's to lower 80's for highs Friday and
Saturday, and lows will generally be in the lower to mid 60's
Thursday night, middle to upper 50's Friday night (lower 60's along
the immediate coast), and upper 50's to lower 60's Saturday night.
MM/25

EXTENDED TERM /Sunday Through Wednesday/...Zonal flow in the
upper-levels will be over the region on Sunday. A surface ridge,
located off the Eastern Seaboard will keep the area mostly dry,
however, with southerly winds and pwats increasing to near 1.8
inches, kept a slight chance of PoPs for regions near and south of
the I-10 corridor Sunday afternoon/evening through Monday morning.
By Monday, confidence begins to lower as models begin to diverge.
Euro pushes an upper-level trough, with an associated surface low,
eastward across the central US, eventually pushing a frontal
boundary towards our region. This solution would lead to increased
PoPs on Monday. On the other hand, GFS and its ensembles show more
progression of the upper-level flow, with the trough digging over
the Eastern Seaboard on Tuesday. This solution would lead to drier
conditions, as the trough would be well to the east of our region.
Due to this uncertainty, kept PoPs at 30 percent for the entire
region on Monday. Models come back into agreement on Tuesday as a
ridge builds over the central US. PoPs drop to slight chance as the
ridge builds and moves eastward. By Wednesday, moisture begins to
increase again as a deepening upper-level trough dives into the
Southern Plains and begins to approach our region.

High temperatures throughout the period will remain in the low to
mid 80s, possibly decreasing slightly on Wednesday to upper 70s to
lower 80s. Lows will range from the mid 60s well inland, to low 70s
by the coast. /96

MARINE...Moderate southeasterly flow is expected through this
evening and small craft operators may need to exercise caution
times over the open Gulf waters. Winds and waves may be locally
higher near scattered to numerous showers and storms through
Thursday. A weak cold front moves through the marine area, but
winds are currently only expected to be light from the north
following the passage of this feature. East to southeast flow will
increase this weekend, particularly going into Sunday when small
craft operators may once again need to exercise caution over the
offshore waters. /21

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...High Rip Current Risk until 5 AM CDT Thursday for ALZ265-266.

FL...High Rip Current Risk until 5 AM CDT Thursday for FLZ202-204-206.

MS...None.
GM...None.
&&

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