Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 211714 AAB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1214 PM CDT Sat Apr 21 2018

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


18Z issuance...VFR conditions continue through much of the evening
hours followed by a MVFR ceiling developing around 04-06Z then
lowering to IFR later tonight. Light fog will be possible during
the late night hours. A few showers will be possible through much
of tonight followed by numerous showers with embedded storms
developing over southeast Mississippi and southwest Alabama
through Sunday morning. East to southeast winds near 10 knots this
afternoon decrease a bit to 5 to 10 knots tonight then become
southeast 10 to 15 knots Sunday morning. /29


.PREV DISCUSSION... /issued 725 AM CDT Sat Apr 21 2018/

DISCUSSION...Updated for latest aviation discussion below.

12Z issuance...Mid and upper level clouds increasing this morning,
and expect this trend to continue today, with mid layer MVFR
ceilings possible by this afternoon and likely tonight. Will also
likely see MVFR to occasional IFR visibilities in fog late
tonight. Could see some very isolated showers near the Gulf coast
today, and spreading into the region from the west late tonight,
but left out of TAFs attm due to expected very isolated nature and
the fact that most of the latest mesoscale model data keeps best
rain chances delayed until after 12z Sunday. Light easterly surface
winds this morning, becoming primarily east to southeast at 10 to
15 knots late this afternoon and overnight. 12/DS

PREV DISCUSSION... /issued 507 AM CDT Sat Apr 21 2018/

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

UPDATE...Rip current risk along the Alabama and northwest Florida
Gulf beaches will be increasing over the next 24 hours. Wind flow
is expected to become onshore and increasingly strong beginning
late this afternoon and continuing through Sunday. While the rip
current risk is expected to be low today, by early this evening
the strengthening onshore flow will result in a moderate risk of
rip currents tonight and then a high risk by Sunday. Went ahead
and issued a CFW for a High Risk of Rip Currents for Sunday. Will
issue updated ZFP shortly to headline the hazard for beach zones.

PREV DISCUSSION... /issued 432 AM CDT Sat Apr 21 2018/

NEAR TERM /Now Through Saturday night/...A shortwave upper ridge will
move eastward across the central Gulf Coast region today, weakening
somewhat tonight as a large upper level low moves east out of the
southern plains states an approaches the southeastern states.
Meanwhile, southeasterly low level flow will increase through the
day as a cold front begins to approach the region from the west.
Moisture levels are expected to increase enough near the coast for
the possibility of a few light showers by the afternoon. Upper level
height falls ahead of the approaching upper low, in conjunction with
upper diffluence associated with the left exit region of a jet max
rotating through the base of the trough, will serve to increase deep-
layer ascent along and ahead of an attendant surface front tonight,
with chances for showers and storms increasing across the entire
area late tonight. Instabilities will be lacking through tonight
however, so primarily showers expected overnight. Highs today
expected to climb into the low to mid 70s. Min temps tonight a
little warmer than past several nights due to return flow setup off
the Gulf, with lows ranging from the upper 50s over interior
northern zones to the low to mid 60s near and at the coast. 12/DS

SHORT TERM /Sunday Through Monday night/...Will start the short
term period with an upper level low pressure system centered over
southeast KS and NE OK Sunday morning that tracks east southeast
over the Mid-South by Sunday afternoon. Ahead of this system,
geopotential height fields aloft become increasingly diffluent
within the presence of mid level height falls spreading eastward
over the Lower MS River Valley. Wave of frontal low pressure over
AR is forecast to pivot eastward during the day Sunday with an
attendant cold front approaching from the west. East of the cold
front, a warm front is draped in a northwest to southeast
orientation initially over the central portions of the forecast
area and remains in a nearly fixed position there through the day
Sunday. South of the warm front is where slightly better
instability exists, over the coastal zones and offshore. As deep
layer ascent and frontal forcing approach from the west, any
surface based convection south of the warm front, becomes
increasingly elevated over the interior when moving northward
across the warm front. There is low confidence with the degree of
instability in the small warm sector, as presence of thickening
cloud cover could very well lead to lower amounts by a category or
so than advertised in some of the guidance. Also, strength of the
low level wind field varies between model guidance. Given
thoughts on instability/wind fields, severe potential at this time
remains too low for anything higher than a marginal risk. PoP`s
trend markedly higher from west to east thru the day Sunday.
Latest gridded storm total rainfall ranges from 1 to 2 inches, but
some areas could see locally higher amounts. Due to recent
flooding problems over a few areas with the passage of the last
system a week ago, will be watching closely for flooding. It will
not take much time for creeks/streams to respond quickly if we see
any storms move over the same areas for a few hours.

By Sunday night, with the expected eastward progression of showers
and embedded storms thru the area, categorical PoP`s shift to the
far eastern zones with chances tapering back to the west.

As the surface low swings east over northern MS/northern AL Sunday
night, cold front makes passage. With a complex frontal low
extending from southern GA to northern MS into the day Monday,
potential exists for wrap-around moisture to linger over the
interior, where a chance of rain will be mentioned.

High risk of dangerous to potentially deadly rip currents to
remain Sunday and Sunday night along area beaches. /10

LONG TERM /Tuesday Through Friday/...Although upper trof axis is
progged to be positioned to the east of the local area Tuesday,
more energy riding down the base of the trof may be enough to
squeeze out a chance of some more showers as it passes across.
Heading into the mid and late week, a series of fronts make
passage across the Gulf coast. We continue to see a bump in rain
chances along and ahead of the first front Wednesday night which
may linger into the day Thursday before ending. The next front
brings a quick return to rain chances Friday. /10

MARINE...A moderate easterly flow today will become a more southerly
moderate to occasionally strong flow tonight through Sunday night as
a cold front approaches the marine area from the west. Winds are
then expected to become moderate westerly in the wake of the front
by early Monday, with a light to moderate west to northwest flow
then continuing into the middle part of mid next week. Showers and
thunderstorms are expected over the coastal waters in association
with the frontal passage, primarily from late tonight through
Sunday night. 12/DS


AL...High Rip Current Risk from Sunday morning through Monday morning
     for ALZ265-266.

FL...High Rip Current Risk from Sunday morning through Monday morning
     for FLZ202-204-206.



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