Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 170458 AAB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1158 PM CDT Wed Aug 16 2017

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


06Z issuance...Prevailing VFR conditions forecast along the
northern gulf coast region over the next 24 hours. Added vicinity
thunderstorms starting at 17.18z to all TAF sites for developing
afternoon convection, and a PROB30 group from 17.20z to 18.02z.
Light and variable to calm winds overnight will become west at 5
to 7 knots at KMOB and KPNS, turning to the southwest in the
afternoon. Winds at KBFM will turn to the south-southeast due to a
developing bay breeze. /22


.PREV DISCUSSION... /issued 346 PM CDT Wed Aug 16 2017/

NEAR TERM /Now Through Thursday/...Convection will come to an
end this evening as the boundary layer cools due to the loss of
daytime heating. Muggy overnight conditions continue with lows in
the low to mid 70s inland to upper 70s along the coast. Upper
ridging builds over the area on Thursday resulting in less coverage
of showers and thunderstorms. However, with precipitable water
values still around 2 inches, isolated to scattered showers and
storms can be expected with the greatest coverage across
northeastern areas where better deep layer moisture will reside. The
lower coverage of showers and thunderstorms will result in high
temps in the low 90s inland to upper 80s along the coast. /13

SHORT TERM /Thursday night Through Saturday night/...Upper ridging
centered over the north central Gulf Coast Thursday evening will
begin to get shunted westward with the approach of an inverted
trough axis from the east. Any shower and storm activity we see
on Thursday should quickly wane with the loss of heating in a
generally subsident environment associated with the ridge.

Moisture levels will be on the increase Friday as the influence of
the approaching trough sends precipitable water values back to
near or above the 2 inch mark by Friday evening. With deeper
moisture in place and more favorable large scale lift, we will see
an increase in shower and storm coverage for Friday. Forecast
soundings show around 2000 J/kg of MLCAPE and some modestly dry
air in the mid levels of the atmosphere across the area Friday
afternoon. Will have to watch any storms that form in this
environment as they will be capable of gusty downburst-type winds,
heavy rain and frequent lightning. Certainly not expecting
widespread severe weather but the strongest thunderstorm cores
could produce winds approaching 50mph given the dry air noted in
the mid levels.

The upper trough axis sets up across the area on Saturday resulting
in more widespread cloudiness, showers and storms. Will carry likely
pops across the southern half of the area with chance pops across
the northern tier. Area forecast soundings continue to show
around 2000 J/kg of MLCAPE for Saturday and any of the stronger
storms will be capable of the usual summer time threats of heavy
rain, frequent lightning and localized gusty winds where the
stronger thunderstorm cores collapse.

Temperatures will not vary much over the short term with low to
mid 90s expected inland and upper 80s at the coast. Heat index
values will be in the 103-107 range on Friday and tad cooler on
Saturday. Lows will remain in the mid 70s inland to around 80
along the immediate coast. 05/RR

LONG TERM /Sunday Through Wednesday/...Deep layer moisture and
modest support for upward motion associated with the trough axis
will persist on Sunday. Precipitable water values will continue
near or above the 2 inch mark. General shower and storm coverage
will be similar to Saturday with areas of likely pops over
southeast MS with chance pops elsewhere.

Medium range models begin to diverge with respect to timing and
placement of the upper level features into early next week. The
ECMWF keeps the weakening trough in place across the north central
Gulf Coast. The operational GFS tries to build upper ridging
across the area but a quick glance at the GFS ensemble height
anomalies looks more like the ECMWF solution. Will side with the
more consistent Euro solution and keep chance pops across the area
Monday and Tuesday and decrease to slight chance for Wednesday as
ridging builds back in.

Temperatures will remain at seasonal levels through the extended
forecast period...generally low 90s during the day and mid to
upper 70s for lows.

Eclipse: Monday afternoon is still pretty far out in the long range
for a truly skillful cloud cover forecast but a cursory glance at
model relative humidity through the column shows the potential
for a few low level cloud layers around during eclipse time. Cloud
cover climatology across the southeast US at roughly mid-day in
August is not typically favorable for clear skies but stay tuned!

MARINE...A ridge of high pressure from the western Atlantic across
the north central Gulf will remain in place through the end of the
week. This will maintain a generally light to occasionally moderate
west to southwest wind flow. A weak front will approach late in the
weekend resulting in a higher coverage of showers and thunderstorms.
Winds and seas will be locally higher near thunderstorm activity.




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