Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 051226 AAA
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
626 AM CST Mon Dec 5 2016

.DISCUSSION...See updated information for land areas and aviation
discussion below.

&&

.UPDATE...Surface observations indicate that patchy fog persists
across much of the region early this morning, with visibility still
locally reduced to 1/2 to 1 mile in some spots. We have added patchy
fog mention through the mid-morning hours. Continued southerly swell,
along with high tidal ranges and increasing southerly winds tonight
have warranted the issuance of a high risk of rip currents along area
beaches again today and tonight. /21

&&

.AVIATION...
12Z issuance...Widespread IFR to LIFR conditions this morning, with
low overcast stratus decks of 200-700 ft AGL and fog reducing the
visibility to less than 2 SM at times, locally down to 1/2 SM. Expect
Visibility should slowly improve this morning, but expect low cigs to
persist today, potentially only rising to MVFR at best. Expect
widespread SHRA to move into the region late this morning and this
afternoon, with locally heavy rain reducing visibility. Scattered
TSRA will also be possible, a few of which could become severe late
this afternoon into tonight. Winds should gradually become southeast
to south by this evening. /21

&&

.PREV DISCUSSION... /issued 504 AM CST Mon Dec 5 2016/

..Locally Heavy Rainfall and a Few Severe Thunderstorms Possible...

NEAR TERM /Now Through Monday night/...A deep upper level low
continues to slowly move across northern Mexico early this morning,
and is centered just south of the Texas Big Bend. A moist southwest
flow pattern aloft extends across our forecast area well in advance
of this feature early this morning, with precipitable water values
generally averaging between 1.5" and 1.7" across the region. An
interesting surface pattern is in place early this morning, as a
stationary frontal boundary extends across much of the northern Gulf
of Mexico from south of LA to near the FL Big Bend. Northerly
surface winds and cool temperatures in the 50s to lower 60s are in
place over most of the area, except for a southeasterly wind and
temperatures around 70 around the Destin area near the boundary.
Radar is indicating a temporary break in shower activity as of 4 AM
CST, but surface observations indicate that some patchy fog has
developed around the area with visibility values locally reduced to
1/2 to 1 mile in a few places. We have added some patchy fog to the
forecast through the early morning hours and will continue to
monitor trends.

The active weather event we have been advertising the past few days
still looks on track to impact our forecast area today and tonight.
The upper level low will move eastward toward south central TX
today, before finally ejecting northeastward as a shortwave trough
toward the ArkLaTex vicinity this evening and the Mississippi and
Tennessee Valley regions late tonight into early Tuesday morning.
Surface low pressure will meanwhile deepen near the TX/LA coast this
afternoon, before lifting northeastward toward the Mississippi
Valley this evening, and into TN late tonight into early Tuesday
morning. The surface warm front will likely remained positioned
offshore this morning, with the possible exception of near the
northwest FL coastline. MLCAPE values should therefore average less
than 200 J/KG over most of the region this morning and afternoon,
except perhaps a bit higher between 200-500 J/KG near the northwest
FL coast in the vicinity of the boundary. Short range and high
resolution models are in agreement that large scale lift will spread
over the area, especially after the noon hour, with a signal for
potential of locally heavy rainfall developing over southern
portions of the forecast area this afternoon, where precipitable
water values could rise to an impressive 2.00" or so. WPC QPF
guidance of 1.00"+ of rainfall during the noon-6 PM CST time frame
south of a Mobile-Andalusia line looks reasonable, and will mention
the locally heavy rain potential in the forecast this afternoon
across these areas. We will have categorical (90-100%) POPs in the
forecast during the afternoon. If a few cells moving off the
northern Gulf can tap into some instability near and south of the
boundary close to the coast, will have to closely monitor for a few
rotating storms with wind/isolated brief tornado potential near the
immediate coast this afternoon. Highs today should range from the
lower to mid 60s in the cooler sector along and northwest of I-65,
and the upper 60s to lower 70s generally southeast of I-65.

Surface flow will turn more southeasterly, then southerly this
evening and tonight as the warm front finally begins to pull
northward across the forecast area courtesy of the surface low
lifting toward the Mississippi and Tennessee Valley region. Surface
dewpoints should gradually rise into the mid to upper 60s as the
warm front advances north, possibly around 70 near the immediate
coast. Low level moistening should contribute to MLCAPE values
rising to 200-600 J/KG across much of the forecast area this
evening. Shear should also strengthen this evening ahead of the
ejecting shortwave trough, with short term guidance indicating a 40-
50 kt low level jet developing over our forecast area late in the
evening. Increasing shear and modest instability could contribute to
at least a limited severe weather threat over much of our area this
evening into late tonight as additional convection develops ahead of
the advancing cold front. Damaging wind gusts along with an isolated
tornado or two will be possible this evening, until around 3-4 A.M.
Tuesday morning until surface winds veer with the passing front. We
have mentioned isolated severe storms in the forecast tonight, and
will continue to highlight the limited severe potential in the
HWO/graphicast. Lows tonight will range from the mid 50s to around
60 over western portions of the area, to the mid to upper 60s over
the far eastern and southeastern zones. /21

SHORT TERM /Tuesday Through Wednesday night/...Showers and
thunderstorms will move east out of the area Tuesday morning with a
drier airmass filtering into the region through the afternoon.
However, no cold air follows this front as an upper level southwest
flow develops as another trough digs across the western states. Highs
on Tuesday will be in the low to mid 60s inland to upper 60s and low
70s near the coast. Tuesday night lows will be in the mid 40s inland
to low 50s along the coast. Wednesday will be dry and mostly clear
with highs in the low 60s inland to mid 60s along the coast. /13

LONG TERM /Thursday Through Sunday/...A strong cold front will move
rapidly through the area Thursday morning as an upper trough digs
across the eastern states. A much colder and drier airmass will
follow in the wake of this front for the end of the week. A few
scattered showers are possible during the day as the colder air acts
to squeeze any available moisture out. Rainfall totals will remain
light. Thursday will feature steady or falling temps during the day
with gusty northwest winds making it feel even colder. Highs will
only be in the low to mid 50s inland to low 60s near the coast.
Thursday night lows fall into the mid and upper 20s inland to mid 30s
along the coast. Winds will decrease on Friday but temps will
struggle to reach the low to mid 40s as Arctic high pressure builds
southward. Friday night will be the coldest of the period as the high
settles over the area. Lows will fall into the low to mid 20s inland
to low and mid 30s along the coast. A moderating trend develops over
the weekend as the high moves east of the areas and an east to
southeast flow develops. /13

MARINE...A warm front will remain oriented over the northern Gulf
near the immediate coast today, but will gradually lift northward
this evening as low pressure moves toward the Mississippi and
Tennessee Valley region. Southwest to west flow will become strong
over the offshore waters, as well as the Mississippi Sound and Lower
Mobile Bay tonight and Tuesday morning, and have issued a Small
Craft Advisory for these areas during this time frame. Seas will
build to 5-7 feet tonight into Tuesday. Winds become northwest
Tuesday night following a frontal passage. A more significant cold
front will move through the marine area Thursday and will bring
strong offshore flow and building seas through Friday. /21

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...High Rip Current Risk through late tonight for ALZ265-266.

FL...High Rip Current Risk through late tonight for FLZ202-204-206.

MS...None.
GM...Small Craft Advisory from midnight tonight to noon CST Tuesday
     for GMZ631-632-650-655-670-675.

&&

$$

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