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Area forecast discussion...updated 
National Weather Service Mobile Alabama
1149 PM CDT Monday Sep 15 2014

Aviation (06z issuance)...will have VFR conditions continuing
through Tuesday morning and while there still is a small potential
for clouds below 1000 feet and/or light fog developing during the late
night/early morning hours...potential is too low to include in a
tempo group at this time. Will kept a thunderstorms in the vicinity beginning at 17-18z
with a tempo group during the early to middle afternoon hours for MVFR
conditions in thunderstorms and brief IFR conditions will be
possible in the stronger downpours. /29


Previous discussion... /issued 11119 PM CDT Monday Sep 15 2014/

Update...have lowered probability of precipitation to slight chance probability of precipitation for the remainder
of the night as convection continues to decrease in coverage. Made
other minor adjustments. /29


Short term (tonight and tuesday)...the main large-scale change
during the next 24 hours is that westerly flow in the middle- and upper
troposphere becomes northwesterly by Tuesday as a longwave trough moves
through the Ohio Valley region. The elongated ridge of today will be
replaced by a deep northwesterly flow. Ahead of the surface cold front...a
deep layer of clouds advect into the region overnight from the north
and combined with sufficient ingredients for additional
rainfall...Tuesday should be wetter than today. Thus rain chances in
the likely category for southern 2/3rds of the area tomorrow along
and ahead of the front. There is notable large scale low level
confluence (and computed convergence) in the wind field along the
front as it moves through tonight. Boundary layer winds become
northerly during the course of the day on Tuesday and weak surface
high pressure becomes established. Leftover showers and
thunderstorms this evening will play a role in moistening the local
atmosphere ahead of the approaching front this evening. Have left
probability of precipitation a little elevated in the overnight period due to this reason.
Made no significant departures on maximum or min temperatures. Many areas stand
to receive between a quarter and a half inch through tomorrow
afternoon this time. Some areas could have isolated totals up to an
inch (higher locally where several thunderstorms move over the same
area). 23/jmm

(tuesday night through Wednesday night)...we expect that the
aforementioned front will have moved southeast according to GFS
numerical guidance by Tuesday evening. Indications are that it will
push south over the northern Gulf Tuesday night...bringing a chance
of showers and isolated thunderstorms through at least the first 3
hours of Tuesday evening and mostly along and south of I-10. By
midnight Tuesday we expect the convection to have moved offshore.

The major actors noted include a 500 mb ridge over The Rockies will
remain stationary through Tuesday night and then start to move east
Wednesday while at the same time a long wave upper trough will deepen
over the eastern United States and also move east. We expect these
features will help maintain the structure of the frontal system and
finally push it offshore Tuesday night.

Numerical outputs regarding the thermodynamic picture indicate the
bulk of convective ingredients will be south of I-10 as of
18... Li as shown by the sounder is initialized somewhat too
low compared to the 15.12z GFS and compared to the lix sounding.
However the precipitable water is pretty close agreement on all
three. Cape is averaging about 1600 with a maximum of 2200. Lifted
index is averaging -4 degrees which has been pretty typical for the
last few weeks during daylight. Precipitable water will remain just
around 2 inches. By 18.06z that should be dropping rapidly...but loss
of sunlight will further lower the chances of rain north of I-10. We
therefore expect likely chances of measurable rain in which short
periods of heavy rainfall...gusty winds...and frequent lightning will
be produced by some thunderstorms into early Tuesday evening. Average
rainfall totals would range from 0.25 to 0.75 inches per 12 hour
period in our area tonight through Tuesday with locally higher
rainfall 2 to 3 inches possible in some locations. As of 18.18z there
will likely will be no impetus for convection at all...and clearing
skies are expected as well.

Forecast highs Wednesday rebounded a bit...about 2 degrees inland
and most likely due to decreasing sky cover. They will be about 4
degrees above normal...and 2 or so below normal Tuesday night. For
Wednesday night...mav guidance has lows 2 degrees cooler than the
last model output which would put it about 5 to 7 degrees below
normal Wednesday night. We raised that a smidgen to match neighbors
but parts of the northern inland regions still make it down to 62.

77/blowing dust

Long term (thursday through monday) significant changes to the
forecast. GFS and Euro are both phased pretty closely. The
wave number 5 model calculations indicate the deep upper trough over
the eastern United States will hang on Thursday and
Friday...dampening through this weekend and allowing a ridge to
build in the west Atlantic region around 60 degrees west. However by
Friday we should see isolated popcorn type afternoon showers and
thunderstorms close to shore. Meanwhile a weak surface front would
move through our region with an offshore push indicated thus far.
Once that happens...a surface ridge would dominate our weather
picture as well as the rest of the southeastern United States
through Monday. This would bring clear to partly cloudy and skies
and to isolated chances of measurable rain through much of the
extended period.

Highs will be around 2 to 3 degrees above climatological normals
Thursday through Friday...and around normal Saturday through Monday.
Lows inland Friday will be about 3 or 4 degrees below normal when
compared to points a little north of our area....easing closer to
normal by next week. 77/blowing dust

Marine...a weak frontal boundary remains nearly stationary along or
just inland from the Gulf Coast through much of the week with a weak
high pressure ridge to the south out over the eastern Gulf of
Mexico. By Thursday and Friday the front to the north gets a push...
and moves south across the marine area with stronger high pressure
building in from the north. Prior to the frontal passage...primarily a light
to moderate westerly flow will continue...with a diurnal northwesterly
component overnight and more of a southwesterly component during the
afternoon. By the weekend...the building ridge to the north will
result in a stronger and more steady easterly wind flow over the
marine area. Seas initially in the 2-3 foot range over the marine
area tonight...then around 2 feet or less for most of the remainder
of the week...before beginning to build going into the weekend with
the increasing easterly flow. Isolated to occasionally scattered showers
and storms over the coastal waters...primarily overnight and early
morning hours. 12/ds


Preliminary point temps/pops...
Mobile 73 89 71 91 70 / 30 60 30 20 05
Pensacola 75 88 74 91 71 / 40 60 40 10 05
Destin 76 88 75 89 74 / 40 60 40 20 05
Evergreen 70 90 67 91 63 / 40 60 20 10 05
Waynesboro 70 90 66 90 64 / 20 50 20 10 05
Camden 70 90 66 89 62 / 30 40 20 10 05
Crestview 71 90 68 92 64 / 40 60 30 10 05


Mob watches/warnings/advisories...


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