Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 201754 AAC
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1254 PM CDT Sun Aug 20 2017

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

&&

.AVIATION...
18Z issuance...Predominate VFR conditions are expected through the
TAF period. Drier air over the area will result in fewer storms
this afternoon. Better moisture will work its way into the area by
midday Monday, resulting in a better chance of isolated to
scattered storms. However, it appears the most likely time frame
for storms will be just after the current TAF period ends, so did
not include a mention of thunder in this forecast. 34/JFB

&&

.PREV DISCUSSION... /issued 1047 AM CDT Sun Aug 20 2017/

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

UPDATE...A deep layer east to northeast flow is resulting in a
wedge of drier air moving into the area, particularly along and
east of I-65. GOES-16 total precipitable water showing values as
low as 1.2-1.4" across inland southwest and south central Alabama.
This drier air will result in a storm free day for a good portion
of the area. Best chance for isolated to scattered afternoon
storms will be across southeast MS and along coastal AL where deep
layer moisture will be more sufficient. Lesser rain coverage will
mean high temps will climb a little higher. Highs are expected to
reach the mid 90s away from the coast, with a few upper 90s
possible over south central AL. Highs in the lower 90s closer to
the coast. Heat indices will again range from 100 to 107 degrees,
highest in coastal areas and west of I-65 where dewpoints will
likely not mix out as much. Overall forecast is on track and only
made minor changes. 34/JFB

PREV DISCUSSION... /issued 702 AM CDT Sun Aug 20 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...
20/12Z issuance...VFR conditions will generally prevail through
the period. Isolated showers and storms will be possible this
afternoon, but coverages not enough to include anything more than
VCTS at TAF locations. Surface winds light and variable through
most of the period, but becoming predominately east to southeast
for a period of time this afternoon. 12/DS

PREV DISCUSSION... /issued 444 AM CDT Sun Aug 20 2017/

NEAR TERM /Now Through Sunday night/...An upper low over the east central
Gulf of Mexico will move very slowly to the west through the period,
and be located over the west central Gulf by late Sunday night into
early Monday morning. As this upper low drifts slowly west, a ridge
of upper level high pressure will begin building over the forecast
area from the east. Meanwhile, surface high pressure ridges into the
forecast area from the northeast, bringing in a wedge of drier air
in the low and mid levels into the northeastern portions of the
forecast area. This will maintain a moisture gradient across the
area, with precipitable water values around 1.5 inches over
northeast zones and up to around 1.9 inches closer to the coast and
across southeast Mississippi. This set-up would tend to keep any
chances of precipitation more confined to our western and coastal
zones, as has been the case over the past few days, and this in
what we expect again today. However, due to the combination of the
building upper ridge and dry airmass, we expect convection to be
more limited in coverage today than past couple of days,
especially over interior eastern zones. The highest chances for
showers and storms (30%) today are expected to be over interior
southeast Mississippi, with isolated (20%) PoPs expected over
interior southwest Alabama (generally to the west of I-65) and
over the Alabama and western Florida panhandle coastal counties.
Over the interior eastern half of the forecast area (generally
north of I-10 and east of I-65, will keep rain chances out of the
forecast today, as that is where the drier airmass is and the
influence of the building upper ridge will be the greatest. Any
showers and storms that do develop today will quickly dissipate
shortly after sunset today, with no PoPs needed for tonight.
Otherwise, hot and muggy conditions will continue. Highs today
will again be in the low 90s near the coast and mid 90s for most
inland locations. These max temps combined with dewpoints in the
low to mid 70s will lead to heat index values ranging from around
101 to 107 degrees today. Lows tonight will range from the low to
mid 70s inland to upper 70s along the coast. 12/DS

SHORT TERM /Monday Through Tuesday night/...Will begin the short
term period with a west Atlantic mid-level ridge axis nosing west
into the Lower Mississippi River Valley with a large upper
tropospheric trof/low (TUTT) positioned over the central Gulf. The
position of the deep layer ridge remains mostly unchanged thru
the period while the Gulf TUTT gradually shifts westward to over
the western Gulf. At the surface, high pressure off the mid-
Atlantic/southeast US coast noses westward over the central Gulf
coast. As the Gulf TUTT tracks west of the local area, deep layer
Gulf moisture modifies thru the first half of the week. Combine
this with sufficient daytime instability and mid level impulses
propagating from southeast to northwest around the larger scale
upper level circulation with the westward moving Gulf TUTT favors
modest chances of showers and storms each day. With that being
said, expected increase in cloud cover on Monday could hamper
viewing of the solar eclipse. Daytime highs Monday and Tuesday in
the lower to mid 90s along and north of I-10 with numbers ranging
from the upper 80s to near 90 closer to the coast.

A diurnal decrease in convective activity is expected each night
over the interior, with the focus shifting southward to over the
Gulf waters and potentially coastal zones. Overnight lows reflect
little change, ranging mostly in the mid 70s interior to upper 70s
beaches. /10

LONG TERM /Wednesday Through Saturday/...A broad high level trof
over the Great Lakes to the Tennessee River Valley on Wednesday,
sharpens by Friday from the Mid-Atlantic to the Appalachians. This
feature allows a surface cold front to push south through the mid
Mississippi River and Tennessee Valleys on Wednesday before
stalling it somewhere across the local area by the close of the
week. The front will serve as a focus for ascent with modest chances
of showers and storms remaining in the forecast into the latter
half of the week as the environment ahead of the boundary remains
seasonally hot and humid.

Daytime highs look to range from the lower half of the 90s
interior and around 90 along area beaches. Overnight lows in the
lower to mid 70s interior Wednesday night may potentially dip into
the upper 60s in a few spots generally over the northwest zones
by Friday night, with the front south of the these areas by then.
Overnight lows reflect little change over the beaches, ranging
mostly in the mid to upper 70s /10

MARINE...A surface high pressure ridge will build in from the east
today and persist into the middle part of the week. This pattern
will result in a variable light wind flow pattern today becoming
more east to southeast through midweek. A weak frontal boundary is
expected to approach the marine area late in the period with winds
remaining light but possibly becoming more southwest to west if
the front slips offshore. Little change in seas expected through
the period. Winds and seas will however be locally higher in and
around isolated to scattered showers and thunderstorms. 12/DS

&&

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

$$

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