Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 231130 AAA

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
630 AM CDT Thu Mar 23 2017

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


12Z issuance...VFR conditions overnight will become MVFR during
the day on Thursday. Light northeast winds this morning shift to
southeasterly and increase to around 10 to 15 knots Thursday
morning and afternoon. /13


.PREV DISCUSSION... /issued 503 AM CDT Thu Mar 23 2017/

NEAR TERM /Now Through Thursday night/...An upper level ridge
will build eastward across the central Gulf Coast today and
tonight. Meanwhile, a sfc ridge of high pressure will build across
the Mid-Atlantic states and Eastern Seaboard with an associated
ridge axis building southwestward across the area today. This will
allow an east to southeast flow to develop and increase as the
sfc gradient tightens. The southeast flow will bring increased
moisture into the area, especially eastern areas. This will result
in increasing clouds and the possibility of a very isolated
shower over mainly eastern portions of the area where the best
moisture will reside. However, the coverage is expected to remain
well below mentionable levels and will keep today dry. The
southeasterly flow and increasing clouds will keep temps slightly
cooler today, especially across eastern zones. Highs will range
from the low to mid 70s in the east to upper 70s and low 80s
across the western half of the area. Lows tonight will range from
the mid and upper 50s to around 60 inland to low 60s along the
coast. /13

SHORT TERM /Friday Through Saturday night/...An upper level
ridge axis extending from the western Gulf of Mexico through the
central Gulf Coast region and southeastern states early Friday
morning will gradually shift eastward Friday afternoon through
Friday night as an upper level low and associated trough axis
translates eastward across the central and southern Plains states.
The surface ridge of high pressure will also shift eastward into
the western Atlantic Ocean through Friday night as the surface low
advances from the Plains toward the Mid-Mississippi Valley region
and the trailing cold front pushes eastward across the ArkLaTex
region and toward the Lower Mississippi Valley. Our forecast area
will largely remain under the influence of the eastward moving
upper level ridge Friday, but weak lift underneath increasing
southwest flow aloft may result in the development of isolated
light rain showers over southeast MS by Friday afternoon. Will
continue to trend high temperatures near or a little above the
warmest guidance values Friday, with forecast readings in the
upper 70s to around 80 over inland areas and mid 70s along the
coast and beaches.

Large scale ascent ahead of the eastward moving upper level
low/trough and the eastward advancing cold front will aid in the
organization of a line of showers and thunderstorms across the
Lower Mississippi Valley region Friday evening. This line will
continue to move eastward across MS and eastern/southern LA
through late Friday night, but short range guidance keeps the bulk
of this convection to the west of our CWA prior to 12Z Saturday
morning. However, isolated to scattered cells could develop over
southeast MS and adjacent far southwest AL overnight Friday night
in advance of this approaching line. We will therefore maintain a
20-30% chance of showers and storms mainly west of a Grove Hill to
Mobile line after midnight. Better instability and shear stays
focused well to our west, so the severe threat late Friday night
appears minimal/unlikely. Lows Friday night should mostly range
in the upper 50s to lower 60s.

The upper level low will continue to lift across MO during the day
Saturday, while its associated trough axis/surface boundary
progresses eastward from the Lower Mississippi Valley toward the
central Gulf Coast region. A shortwave trough embedded in the base
of the larger scale trough axis will lift across southeast MS and
into southwest/south central AL during through the day Saturday,
aiding in the continued development of scattered to numerous
showers and thunderstorms over our region. We will keep the likely
coverage of POPs focused over southeast MS and adjacent southwest
AL Saturday morning, with increasing coverage spreading eastward
over most of the remainder of the region by Saturday afternoon. A
moist and fairly unstable airmass will be in place across our
forecast area Saturday, though the amount and eastward extent of
instability remains somewhat uncertain. Still, with potential
MLCAPE values up to between 500-1000 J/KG, 25-35 knots of 850-700
mb flow, and 100-200 m2/s2 storm relative helicity, there is
potential for some storms to produce strong to locally damaging
wind gusts Saturday. Isolated severe threat may be most pronounced
generally to the west of I-65 Saturday, where guidance indicates
the best coincident shear and instability, but again the eastward
extent of shear/instability still remains uncertain. The new SPC
Day 3 outlook places most area within a slight risk of severe
weather Saturday which agrees with this thinking. Will continue to
mention the potential for a few severe storms Saturday in the HWO
and also local graphics. A chance of showers and storms may
linger at least into the evening hours Saturday before a drier mid
level airmass moves in late Saturday night. However, the overall
severe threat diminishes along with decreasing instability and
shear. Highs Saturday should range in the mid to upper 70s, with
lows Saturday night once again mostly in the upper 50s to lower
60s. /21

LONG TERM /Sunday Through Wednesday/...A drier mid level zonal
flow pattern returns across the forecast area Sunday, though the
ECMWF and to some extent, the GFS indicates residual weak lift
which could support lingering isolated convection. We will
maintain a 20% POP Sunday over most areas. The next in a series of
upper level troughs is progged to translate across the Mississippi
Valley region Monday. Increasing ascent and sufficient instability
could support additional scattered showers and thunderstorms
across the region Monday and Monday night, a few of which could be
strong over the interior. Some uncertainty on the evolution of the
mid level pattern Tuesday-Wednesday, with potential for increased
ridging aloft, but enough instability/weak shortwave impulses
could support at least isolated thunderstorms both days. Will keep
low POPs in the forecast both Tuesday and Wednesday. Temperatures
should continue to remain quite warm each day through the extended
forecast period, with highs each day averaging in the upper 70s to
lower 80s with morning lows in the upper 50s to mid 60s.

MARINE...An area of high pressure will build over the Mid-
Atlantic and western Atlantic while and area of low pressure
develops over the plains through the end of the week. As a
result, a moderate to strong onshore flow will develop along with
increasing chances of showers and thunderstorms by this weekend.


GM...Small Craft Advisory from 4 PM this afternoon to 1 AM CDT
     Saturday for GMZ631-632-650-655-670-675.



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