Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 030455 AAC
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1055 PM CST Fri Dec 2 2016

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

&&

.AVIATION...
06Z issuance...Satellite shows expansive and thickening cloud cover
spreading northeast off the east Pacific across Mexico and into Texas,
then eastward into the southeast US. Cig bases are forecast to be at
mid and high levels with VFR conditions forecast. A few light
sprinkles possible out of the higher level cloud deck around or
shortly after 03.06Z. A slight chance of -RA during the day Saturday.
A general light northeast wind flow is forecast overnight. A modest
pickup in east northeast winds is forecast on Saturday, which could
be gusty at times. /10

&&

.PREV DISCUSSION... /issued 955 PM CST Fri Dec 2 2016/

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

UPDATE...Upper air analysis this evening shows a vigorous upper
level storm system centered over the northern Baja Peninsula and
continues to dig south southeastward. This system is tapping moisture
from the east Pacific, bringing an expansive area of thickening
cloud cover across Mexico and Texas, eastward into the southeast US.
Latest 03.00Z soundings at LIX show a continued dry layer up to 775
millibars where it then quickly moistens up aloft, about 8 kft off
the surface. Further upstream at LCH, the moist layer is lowering to
about 5 kft off the surface. Radar is showing some returns moving
northeast across southern Mississippi, but with the drier air in the
low levels, no measurable rain being reported. Will take awhile
longer before the low levels moisten up enough for rain to measure,
which could be as early as daybreak Saturday. Rain chances
to increase thru the course of the day Saturday as a series of mid
level impulses in the high level southwest flow, move northeast
across the central Gulf coast. /10

PREV DISCUSSION... /issued 530 PM CST Fri Dec 2 2016/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...
00Z issuance...Satellite shows expansive and thickening cloud cover
spreading northeast off the east Pacific across Mexico and into Texas,
then eastward into the Lower Mississippi River Delta. Cig bases are
forecast to be at mid and high levels with VFR conditions forecast.
A few light sprinkles possible out of the higher level cloud deck around
or shortly after 03.06Z. A slight chance of -RA during the day
Saturday. A general light northeast wind flow is forecast overnight.
A modest pickup in east northeast winds is forecast on Saturday,
which could be gusty at times. /10

PREV DISCUSSION... /issued 400 PM CST Fri Dec 2 2016/

NEAR TERM /Now Through Saturday/...An upper level trough continues
to dive into northern Mexico, resulting in strong southwest flow
aloft and the advection of moisture...and thus cloud decks...over the
area this evening and overnight tonight. At the surface, an area of
high pressure extending from the northern Plains southeast into the
Southeastern U.S. is maintaining dry, northeasterly flow across the
region into tonight. The high pressure then pushes off to the east
early Saturday and low pressure begins to develop over the
northwestern Gulf in response to the advancing and deepening upper
level low, which by then will be crossing into central Mexico. This
will result in a return of better mid level moisture to the
area...and while dry air at the surface will initially make it
difficult for any precipitation to reach the surface, gradual
moistening of the low levels via evaporation should eventually prove
successful enough to allow for some accumulations across western and
northern portions of the forecast area Saturday. Have thus included
slight chance to chance POPs across western and northern portions of
the forecast area beginning late tonight and lasting through Saturday
as it appears that is where the axis of best moisture will likely set
up.

Overnight lows tonight will remain a little warmer than last night
thanks in large part to the returning moisture and thickening cloud
decks. Thus, expect temperatures tonight to dip into the low 40`s
inland to around 50 near the coast. Likewise, cloudy skies and
showers will help to keep high temps on Saturday in check, primarily
for inland areas across southeast MS and southwest AL. Expect highs
Saturday afternoon to range from mid 50`s across western inland
counties to mid 60`s across eastern inland counties and all coastal
areas. /49

SHORT TERM /Saturday night Through Monday night/...A deep upper
level low will slowly move across northern Mexico from the vicinity
of the Baja region late Saturday afternoon to just south of the Texas
Big Bend by late Sunday night. Surface low pressure will develop over
south TX by late Saturday and eventually into the adjacent western
Gulf of Mexico by Sunday night. A warm front will extend
northeastward from the surface low and will be draped over the
northern Gulf of Mexico Saturday night, before slowly lifting
northward, potentially hugging the immediate Gulf Coast by Sunday
afternoon. Deep layer moisture within southwest flow aloft will
continue to spread northeastward from Texas to the Mississippi Valley
and central Gulf Coast region Saturday night into Sunday, with
precipitable water values forecast to rise to the 1.5" to 1.9" across
our forecast area by Sunday afternoon or evening. A series of
shortwave impulses embedded within the southwesterly mid level flow
will lift across our region Saturday night into Sunday. Deep layer
ascent will bring increasing coverage of rain showers - especially
over southeast MS and interior southwest AL Saturday night, then
across the remainder of the forecast area during the day Sunday.
Instability will be very marginal across our forecast area along and
north of the warm front during the day Sunday, but there is potential
for the boundary to lift just north of the immediate coast by Sunday
afternoon, where MLCAPE values of 200-600 J/KG could be realized. An
isolated strong storm or two could approach the immediate coast from
the Gulf of Mexico Sunday. However, the overall severe threat Sunday
looks pretty marginal given fairly weak low level wind flow (850 mb
winds of 20-30 knots). Lows Saturday night are forecast to range from
the upper 40s to lower 50s over interior locations and in the mid 50s
to around 60 near the coast. Highs Sunday could have quite a range
over the forecast area, with readings in the upper 50s to mid 60s
over the far interior well north of the warm front, to the lower to
mid 70s near the immediate coast.

The upper low will begin to lift northeastward into south central TX
during the day Monday, before quickly ejecting northeast toward the
Mississippi and Tennessee Valley region Monday evening into late
Monday night. The associated surface low will continue to deepen as
it moves northeast toward southwestern LA during by 18Z Monday. The
surface low should then pull northeastward into MS Monday evening,
then toward the Tennessee Valley overnight Monday night. The warm
front should get pulled northward across the I-10 corridor Monday,
then farther north across the remainder of the forecast area Monday
afternoon into Monday evening as the low pulls northeastward. Surface
dewpoints will rise into the mid to upper 60s as the warm front moves
north, contributing to marginal MLCAPE values of 300-600 J/KG moving
north into the interior through the day. Low level flow remains
weak to moderate through Monday afternoon, with 850 mb speeds of
25-35 knots. However, with the marginal instability and low level
wind flow slowly strengthening along the northward moving boundary,
will need to watch for a few strong to marginally severe storms over
southern portions of the area late Monday morning into Monday
afternoon. Model guidance is in agreement that the low level jet
strengthens Monday evening with 40-50 knots of 850 mb flow over the
forecast area between 6 PM and midnight. A limited severe threat may
materialize over the rest of the interior late Monday afternoon into
the evening hours Monday. Marginally severe wind gusts and an
isolated tornado or two will be the primary concerns. Otherwise,
locally heavy rainfall will be possible through Monday night given
the high precipitable water airmass. Storm total rainfall amounts
between 2 and 4 inches with locally higher amounts are forecast in
the Saturday night through Monday night period. /21

LONG TERM /Tuesday Through Friday/...A cold front will move across
the area Tuesday in the wake of the ejecting shortwave trough.
Isolated showers may still be possible over the eastern part of the
area early Tuesday morning, but dry weather otherwise follows Tuesday
into Wednesday underneath a dry west to southwest flow aloft. The
next trough will move from the Plains states to the eastern CONUS
late in the week, with the associated next and more significant cold
front following sometime late Wednesday or Thursday. A slight chance
of rain could arrive ahead of the front Wednesday night or Thursday,
followed by a much colder and drier airmass to end out the week. Our
latest forecast is calling for highs to only reach the 50s Thursday
and a little colder in the mid 40s to lower 50s by next Friday.
Freezing overnight low temperatures look probable across much of the
area next Thursday and Friday nights. /21

MARINE...Moderate northeast winds continue through the rest of
today, then shift to easterly and strengthen to Small Craft Advisory
levels over Gulf waters tonight into Sunday afternoon. Seas building
to 6 to 8 feet will accompany these stronger easterly winds. A shift
to moderate southerly flow occurs Sunday as a warm front moves
northward over the marine area, bringing with it higher shower and
thunderstorm chances into the early part of next week. /49

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...None.
FL...None.
MS...None.
GM...Small Craft Advisory until 6 PM CST Sunday for GMZ650-655-670-
     675.

&&

$$

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