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Area forecast discussion 
National Weather Service New Orleans la
1156 PM CDT sun may 24 2015

Aviation...

Main concern will be timing of scattered to numerous rain showers/thunderstorms and rain
over the next 24-36 hours. Current activity on radar is likely to
continue to occasionally impact a few terminals overnight and
again on Monday. Otherwise...conditions are expected to vary from
VFR to MVFR with some tempo lower ceilings and visibilities. 22/dew point

&&

Previous discussion... /issued 935 PM CDT sun may 24 2015/

Sounding discussion...
no issues with sounding this evening despite a lower than normal
Ascension rate early on. Adiabatic lapse rate surface to local
around 2900 feet...pseudo to 500 mb where a weak subsidence
inversion is noted then pseudo to tropopause at 133 mb with a
temperatures of -75.8c. An inverted-v moisture profile surface to
3200ft...then moderately moist to 9400ft/710 mb...dry layer to
623mb...then saturated cloud deck near freezing level of
14.1kft/600 mb...deep dry layer above. Winds are veering southeast
through S 15-35kt from surface up to 20kft...then SW 25-30kt to
33kft...a layer of west 10-25kt to 37kft...then SW 25-40kt above.
Peak wind 219/38kt at 49.3kft. Low level helicity is 156
m2/s2...lifted index -5 with a cape of 2390 and precipitable water
1.57". Balloon burst in Pearl River County on Blackwell Road off
Highway 11 north of McNeill at an altitude of 20.9 miles up and
downrange about the same distance. 24/rr

Previous discussion... /issued 833 PM CDT sun may 24 2015/

Update...

Line of stronger thunderstorms extended from near Baton Rouge
south near the lower Atchafalaya River. Tornado Watch 204 was
extended in time until 10 PM for a portion of southeast Louisiana
generally along and west of I-55 along and east of the squall
line. Conditions are only marginally favorable for a brief tornado
or damaging wind gusts...so most areas will likely just receive a
period of heavy rainfall...lightning and wind gusts to around 30
miles per hour. Additional updates will be sent as the line moves east...and
it is possible the Tornado Watch could be cancelled before 10 PM.
22/dew point

Previous discussion... /issued 418 PM CDT sun may 24 2015/

Short term...

Showers and thunderstorms have developed across the area out ahead
of a squall line approaching from the west. With ample moisture in
place along with low level shear and decent instability from the
heating of the day...some of these thunderstorms could produce
gusty winds and even a short lived tornado. The area continues
under a Tornado Watch until 01z/8pm CDT. Already...a few of these
storms have produced strong wind gusts including a 57 miles per hour wind
gust in Biloxi.

The squall line should approach the western part of the area
within the next hour or so and then move into the New Orleans
metropolitan area/Slidell around 7pm or so. The line will continue east
towards the Mississippi Gulf Coast between 8 and 9pm at the
current speed. That said...the line has definitely taken its
time during the day today.

Shower and thunderstorm activity should begin to wane in the wake
of the passage of the squall line overnight although rain chances
are still certainly there.

More shower and thunderstorm activity is expected on Memorial Day
with likely chances across the area with the chance of some strong
storms once again.

Long term...

With the focus on the current situation and the Tornado Watch...
not many changes were made to the long term forecast. Rain chances
continue throughout the week as the pattern of disturbances
rolling in from the east along with high pressure to our west will
keep the Gulf moisture flowing.

Aviation...

Most terminals are VFR with a few observing occasional MVFR due to
low clouds with thunderstorms. Isolated to scattered convection
should see some downward trend with loss of surface heating. Line of
convection over southwest Louisiana has been losing definition over
the last couple hours as it outruns the mesoscale convective vortex that generated it.

Most precipitation should end by 03z...with VFR conditions until
around sunrise...when MVFR ceilings will return. Tomorrow may be
close to a replay of today...with showers in the morning and thunder
in the afternoon.

Marine...

Surface ridge that was draped across the Appalachian
Mountains and into the Gulf of Mexico is shifting east into the
Atlantic. Surface trough to the west of the area over Texas will
continue to keep the local pressure gradient fairly tight. The
result of these surface features will be southeast winds in the 15
to 20 knot range. Exercise caution headlines are up and will
likely continue for much of the week with just a few brief periods
of lower winds. Upper level ridge will try to build in over the
western half of the Gulf of Mexico late this week and into the
weekend. This will weaken the gradient over the coastal waters and
cause winds/seas to relax a bit.

Decision support...

Dss code...green.
Deployed...none.
Activation...none.
Activities...severe weather operations.

Decision support services (dss) code legend
green = no weather impacts that require action
blue = long fused watch/warning/advisory in effect or high
visibility event
yellow = heightened impacts with short fused
watch/warning/advisory issuances; radar support
Orange = high impacts - slight to moderate risk severe; nearby
tropical events; hazmat or other large episodes
red = full engagement for moderate risk severe and/or direct
tropical threats; events of National significance

&&

Preliminary point temps/pops...
mcb 70 83 70 82 / 70 70 50 70
btr 70 84 72 84 / 70 60 60 70
asd 72 82 71 82 / 70 60 50 70
msy 72 83 74 84 / 70 70 50 70
gpt 72 81 73 82 / 70 70 50 70
pql 72 83 69 83 / 60 70 50 70

&&

Lix watches/warnings/advisories...
la...none.
GM...none.
MS...none.
GM...none.
&&

$$

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