Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 281611 AAB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1111 AM CDT Tue Mar 28 2017

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


.UPDATE...Short wave upper level ridge has moved atop the region
today with a surface ridge of high pressure positioned from off
the Mid-Atlantic to the eastern Gulf. To the northwest of this
high, frontal zone was draped from the Ohio River Valley to Lower
MS River Valley, westward to northern TX. Deep layer moisture
(pwats from 1 to 1.25 inches) persists over the southeast US.
Although presence of the ridge aloft acts to counter shower/storm
coverage today, enough deep layer moisture and afternoon instability
will be enough to maintain at least a small chance of convective
development. Coverage though looks to be very isolated with
chances 10-20%. A warm spring day with highs in the lower to mid
80s for much of the area. /10


.PREV DISCUSSION... /issued 654 AM CDT Tue Mar 28 2017/

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

UPDATE...Did a quick update to the current zone forecast mainly
to reflect current conditions mentioning mostly patchy fog for
early this morning and introducing more patchy fog late tonight
and early Wed morning. 32/ee

12Z issuance...MVFR to IFR cigs and visibilities through about
28.14z followed by mostly VFR conditions through about 29.03z then
MVFR to IFR cigs and visibilities through 29.12z. Lower cigs and
visibilities mostly from low stratus and patchy fog this morning
and again late tonight and early wed morning. Winds will be mostly
south at 5 knots or less early this morning then 8 to 13 knots
with gusts to around 20 knots during the late morning and
afternoon hours diminishing to 3 to 5 knots by mid evening...
continuing through 29.12z. 32/ee

PREV DISCUSSION... /issued 605 AM CDT Tue Mar 28 2017/

NEAR TERM /Now Through Tuesday night/...Departing mid level short
wave trof to our northeast is followed by a sharp mid to upper
ridge of high pressure moving eastward over the lower Mississippi
river and central Gulf today and tonight. Ridge axis stretches
from the AL/GA line to the eastern Gulf by 12z Wed. Well to the
west a deep mid to upper low center moves from the lower rockies
to the lower plains by 12z Wed with several mid level impulses
rounding the base of this upper system ejecting east northeast
across east Texas and the mid to lower Mississippi river valley
through tonight. With this pattern weak lift is noted in the mid
levels across the central Gulf coast region today and early
tonight helping to initiate a few isolated showers or
thunderstorms across lower parts of the forecast area early today
then shifting more inland by afternoon. Latest model soundings
continue to show limited surface based instability also through
tonight combined with a moderate capping inversion between 2 and
3 kft. As a result will keep only isolated coverage of showers
and thunderstorms for today...shifting further inland by afternoon
followed by no coverage this evening and overnight. With better
ridging aloft will also continue to mention areas of fog for most
inland locations early today reforming again overnight and early
Wed morning. As for temps due to increased cloud coverage
through tonight will lean very close to the current MAV MOS for
highs today and lean towards the warmer MOS numbers for lows
tonight. Highs today will range from the lower to middle 80s for
inland areas and the mid to upper 70s along the immediate coast.
Lows tonight will range from the lower to middle 60s for all
areas. 32/EE

SHORT TERM /Wednesday Through Thursday night/...Forecast area
will be between weather systems on Wednesday, with upper ridge
axis shifting just to the east of the region and southwesterly
flow developing aloft. It is this southwesterly flow aloft that
will bring in shortwave energy in from the west thursday and
Thursday night, although models differ quite a bit on strength of
of energy. 28/00z GFS is strongest with energy aloft moving in,
ECMWF much weaker and NAM (at least at 12Z Thursday) somewhere in
between the other two solutions. Agree with WPC Model Diagnostic
Discussion this morning that the GFS is very likely showing signs
of convective feedback, which is forcing the much stronger solution,
and as they suggest and we prefer, we will be leaning more toward
the ECMWF at this point. Even so, upper jet moving from west coast
into the central portion of the country through mid week will
carve out a highly amplified upper level trough over the southern
Rockies with an embedded closed mid level low pressure area
developing over the New Mexico Wednesday and then lifting
northeast across Texas panhandle to southern Illinois by late
Thursday night and early predawn hours Friday. At the same time,
the southern portion of the mid level trough is expected to swing
east with axis more or less across our forecast area by sunrise
Friday morning.

A surface low pressure area is still forecast to have develop
over southwest Oklahoma region by early Wednesday and also
reach the southern Illinois/Indiana area by late Thursday night,
with an associated cold front approaching our forecast area from
the west Thursday afternoon and moving east across the area
Thursday night.

Onshore low/mid flow ahead of the system will advect moisture
northward across the region, with precipitable water values
climbing to between 1.5 to 1.7 inches Thursday afternoon and
evening. Models advertise SBCAPE values generally in the 700 to
900 J/KG range on Thursday, with SFC-3km Storm Relative Helicity
values ranging from 200 to 400 M2/S2. A 35 to 40 knot low level
jet is also expected to accompany this system. In addition, models
still suggesting 700-500MB Lapse Rates in the 7 to 7.5 C/KM
range. As such, the pre-storm environment will favor the
development of strong to severe thunderstorms throughout the day
Thursday into Thursday night as a line of numerous storms advances
east through the region. Damaging winds, large hail, and isolated
tornadoes are all possible with this system. The Storm Prediction
Center has now outlooked most of our forecast area with a Slight
Chance for severe weather on Thursday and Thursday evening. in
addition to the strong and possibly severe storms, heavy rainfall
is also possible, with widespread 1 to 2 inches likely.

Temperatures above normal through the period. Highs in the
mid/upper 70s to low/mid 80s. Lows in the upper 50s and lower 60s.


LONG TERM /Friday Through Monday/...The precipitation will then
taper off from west to east late Thursday night and early Friday
in the wake of the cold front, followed by high pressure briefly
building over the region. The dry period will then persist
through the early part of the weekend as an upper ridge and
surface high pressure dominate the southeast states. Precipitation
chances will increase once again early next week as yet another
upper level trough develops to our west and advances east over the
southern plains, with scattered showers and thunderstorms
forecast for Sunday afternoon through Monday. Some indications
that another round of severe weather is possible by Monday and we
will continue to monitor for this possibility. Above normal
temperatures will continue through the long term.  12/DS

MARINE...Expect a moderate onshore flow to continue over the marine
area through early Thu then build by Thu afternoon through early Fri
ahead of an upper level disturbance and surface cold front
approaching from the west. Similar to the last couple of days,
higher wind velocities can be expected each afternoon through Thu
due to afternoon heating or local seabreeze effects. With this
seas will continue to range from 2 to 4 feet offshore with choppy
to occasional rough conditions over area bays and sounds. A
moderate to strong west to northwest flow is expected in the wake
of the front Fri through early Sat with seas building to 4 to 6
ft. 32/EE




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