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Area forecast discussion 
National Weather Service Mobile Alabama
354 PM CDT sun Apr 19 2015

Short term...(tonight through Tuesday night)...for tonight through
Monday...a longwave trough evolves over the
central states tonight and expands to dominate much of the central
and eastern states on Monday. A series of powerful shortwaves
continue to move through the southwest flow aloft over the region
through much of the period. One of these shortwaves has exited the
forecast area earlier today with the water vapor loop showing
abundant dry middle/upper level air having moved into the area.
Another shortwave approaching from the west may allow for isolated
convection to develop during this afternoon in this dry air
environment aloft...and should convection become strong...an
isolated severe storm could occur. Uncertainty exists however as to
whether a rather weak cap over the area this afternoon will be
overcome. The 0-3 km cin seen in the rap13 seems to quantify this
feature well and also matches current radar trends. With insolation
allowing for temperatures to climb in to the lower 80s and warming
progressively eastward through the afternoon...and considering the
rap13 placement of the weakest portion of the cap...may see some
convection develop which would affect mainly a portion of south
central Alabama. Have gone with slight chance probability of precipitation this evening for
this portion and will monitor for development and possible
strong/severe storm development...although given the expected
limited coverage...the overall strong/severe storm potential is
low.

A remnant upper low advancing slowly across Oklahoma/Kansas seen in
current water vapor loop ejects off towards the Ohio River valley
tonight as this feature begins to be absorbed by the expanding
longwave trough. An associated surface low moves off well north of
the area overnight but brings a trailing cold front across the lower
Mississippi River valley...which decelerates while moving through
much of the forecast area on Monday. Will have slight chance probability of precipitation
for the western half of the area late this evening into the
overnight hours for isolated convection along and ahead of the
approaching frontal boundary. One forecast concern is that a
shortwave may lead to a mesoscale convective
system...MCS...developing in the Gulf waters south of Louisiana
which could then follow an 850 mb Theta-E ridge extending into the
forecast area...or instead advance eastward south of the area and
follow a second portion of the Theta-E ridge extending east-west
across the northeastern Gulf.

Unsure at this point how much weight to put on this potential
development into the forecast area and have for now just put in
slight chance probability of precipitation across the entire area for the late night hours.

Will have slight chance probability of precipitation for much of the area Monday morning for
isolated convection then dry conditions are expected for Monday
afternoon. Depending on how the mesoscale convective system evolves and if it develops at
all...may see some strong storms mainly over the northwest Florida
Panhandle late tonight into Monday morning...but this is highly
conditional on difficult to forecast sub-synoptic scale evolutions
and will monitor for now. Lows tonight will be at least several
degrees above normal and mostly in the middle 60s with upper 60s near
the coast. Highs on Monday will be slightly above normal and in the
lower 80s. /29

Monday night through Tuesday night...an upper closed low noodles
around over the Great Lakes during this part of the forecast. A lobe
of energy follows the one that pushes the front across the area
Monday...pushing surface high pressure from over the East Texas quickly
east... to near/off the eastern Seaboard. How far east dictates how
quickly southerly flow returns to the lower Mississippi River and
ultimately the forecast area. The GFS is more aggressive in taking it
eastward...the European model (ecmwf) the least. The result is a 3-5 degree spread in
guidance temperatures amongst the resultant temperatures. Have went in the middle
for the forecast.. temperatures drop into the 50s Monday night...rise into
the upper 70s Tuesday...the rebound up a bit Tuesday night as
compared to Monday night.

Long term...(wednesday on)...Wednesday through Thursday...more
energy swirls around the Great Lakes upper low. This energy pushes a
weak front towards the forecast area...with guidance advertising it pushing to a
point between i20 and i10. The GFS is advertising a bit farther south
positioning...along with a strong shortwave moving over the Southern
Plains and lower miss River Valley. The European model (ecmwf) is farther north and am
hard pressed to see the shortwave. The result is the European model (ecmwf)
advertising a cooler...drier solution than the GFS due to a strong
onshore flow off the Gulf with the approaching shortwave. Have went
in the middle for now...

Thursday night through Saturday...an upper low that had been
noodling around over the Desert Southwest breaks down and gets draw
east into an upper ridge that has developed over the Southern
Plains/lower Mississippi River valley. The European model (ecmwf) is advertising the
upper low over the Great Lakes meandering eastward...to off the New
England coast...whilst the GFS takes a more northerly track...moving
the low over southeast Canada...north of New England. With both advertising
the approaching upper energy over the plains...increase southerly
flow off the Gulf results...with temperatures rising back well above
seasonal...especially for overnight lows. With the abundant moisture
off the Gulf...moisture levels and the chance of rain remain a bit
above a seasonal slight chance.

Saturday night through Sunday night...with the European model (ecmwf) advertising the
SW-eastern Continental U.S. Energy taking a more northerly track than the GFS...the
front that is moves over the forecast area Saturday night into Sunday is
significantly weaker than the GFS. Both are advertising a dry period
this period...just the GFS moves move cooler air in. With the
variability in the forecast that has been present day 5 on in the
forecast...just went in the middle with the temperatures. Temperatures at or above
seasonal continue...with nary a drop of rain in the forecast by the
end of the weekend..

&&

Aviation...
18z issuance...will begin with primarily MVFR conditions then VFR
conditions develop fairly quickly as the low clouds mix out with
southwest winds increasing to 10-14 knots. A MVFR ceiling develops
later tonight near 06z possibly with light fog developing as
well...but this will be limited by southwest winds remaining 5-8
knots. VFR conditions return by 15-16z Monday with southwest winds
11-14 knots. /29

&&

Marine...a light to moderate southwest flow becomes westerly for
late tonight and Monday as a cold front approaches from the west.
The front moves through the marine area Monday night with a moderate
offshore flow in the wake of the front. The flow switches to a
light southeast flow on Tuesday as high pressure shifts eastward
across the region. A primarily light southerly flow prevails
through Thursday while a weak front approaches from the north. The
front moves through the marine area Thursday night with a light
offshore flow in the wake of the front...but a southerly flow
returns on Friday. /29

&&

Preliminary point temps/pops...
Mobile 66 81 56 78 58 / 20 20 05 05 05
Pensacola 68 81 60 78 63 / 20 20 05 05 05
Destin 69 80 62 78 64 / 20 20 05 05 05
Evergreen 64 82 52 79 52 / 20 20 05 05 05
Waynesboro 63 80 51 82 53 / 20 10 00 05 05
Camden 65 81 51 78 51 / 20 20 05 05 05
Crestview 66 82 56 81 54 / 20 20 10 05 05

&&

Mob watches/warnings/advisories...
Alabama...high rip current risk until 7 PM CDT this evening for lower
Baldwin-lower Mobile.

Florida...high rip current risk until 7 PM CDT this evening for coastal
Escambia-coastal Okaloosa-coastal Santa Rosa.

MS...none.
GM...none.
&&

$$

29/16

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