Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA

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FXUS64 KLIX 300100
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
800 PM CDT THU SEP 29 2016

...SOUNDING DISCUSSION...

Drier and cooler air continues to move over the central Gulf
Coast States under a cloud free sky this evening. The
precipitable water (PW) value continues to tumble amid cheers from
most everyone. The PW is now measured at 0.75 inches, which is
well below normal for the last day of September. While there are
no layers even close to saturation with dry air throughout the
column, the bulk of the drier air is above 850mb/5000 feet. Below
5000 feet, the boundary layer is well-mixed a temperature profile
close to the dry adiabatic lapse rate. As was the case yesterday
evening, water vapor imagery nicely displays the drier air over
the region with the driest area along/north of the tidal lakes and
over southern Mississippi moving southward toward and over the
Gulf of Mexico. Winds throughout much of the troposphere are from
the northwest as a sprawling area of low pressure spins over the
Ohio Valley. A peak wind speed of 48 knots was found at 40000
feet.

00z balloon info: A routine flight which ascended for 105 minutes
to a height of 21.1 miles above the ground bursting over Lake
Borgne 25 miles downrange from the office.

Ansorge

&&

.PREV DISCUSSION... /issued 323 PM CDT THU SEP 29 2016/

SHORT TERM...

Very little change in thinking concerning the forecast through the
weekend. Drier and colder air will continue to advect in from the
north on the back of deep layer northwest flow through Saturday.
Strong negative vorticity advection and subsidence will also
dominate the Gulf South. This pattern will keep clear skies and
cooler than average temperatures in place through Saturday. With
light winds and clear skies in place overnight, temperatures
should dip into the middle to upper 50s over inland locations and
the lower to middle 60s over coastal locations both tonight and
tomorrow night.

The deep layer northwest flow pattern will break down Saturday
night and Sunday as a closed low over the Great Lakes gradually
shifts further north and east. However, as a more westerly flow
regime develops in the mid and upper levels, a fast moving and
fairly weak shortwave trough will slide through the upper levels.
This upper level trough will have very little moisture to work
with, and only expect to see an increase in cloud cover as the
trough axis slides through on Monday for the majority of the
forecast area. At most, some moisture in the central Gulf could be
drawn into the outer coastal waters and spark off some isolated
shower activity. Temperatures will begin to modify as the 925mb
thermal trough pulls away from the region. Expect to see lows on
Saturday night only cool into the 60s across most of the region,
and daytime highs should warm back into the middle 80s. Overall,
temperatures should be close to average for early October.

LONG TERM...

Heading into next week, the upper level trough axis is forecast slide
further to the east. This should allow for increased upper level
ridging to overspread the forecast area on Monday and Tuesday
resulting in sinking air throughout the atmospheric column and
clear skies. Dewpoints should remain in the 50s and lower 60s, so
even with the increase in temperatures into the middle to upper
80s conditions should remain rather pleasant. The upper level
ridge should get squeezed by a tropical system off the east coast,
and an approaching long wave trough axis digging into the Plains
on Wednesday and Thursday. With an increase in positive vorticity
advection overspreading the area, a corresponding increase in
forcing aloft should support the development of a few showers and
thunderstorms Wednesday. Moisture is forecast be greatest in the
low levels, and a weak cap should still be in place Wednesday
afternoon. This could limit over convective potential, but a few
thunderstorms could develop along weak seabreeze boundaries during
the afternoon hours. Temperatures are expected to remain quite
warm in the upper 80s, so the formation of a seabreeze is fairly
likely.

A cold front associated with the long wave trough moving from the
Plains into the Midwest should push through the forecast area on
Thursday. Have placed low end chance POP of 30 percent in the
forecast as scattered showers and thunderstorms develop along and
ahead of the advancing frontal boundary. Temperatures are expected
to remain warm in the upper 80s, and the cap should be weaker as
the trough axis approaches and temperatures aloft cool. An
increase in mid-level moisture advecting in with the upper level
trough axis should also assist in weakening the mid-level cap and
supporting the forecast of scattered showers and thunderstorms.

AVIATION...

VFR all terminals through Saturday.

MARINE...

Drier continental high pressure will remain in place
through the weekend and early next week for light to moderate
offshore flow for the forecast period. Some limited convective
coverage along stationary frontal zone in the offshore waters may
encroach the outer coastal waters at times Sunday onward. 24/RR

DECISION SUPPORT...

DSS code: Green.
Deployed: None.
Activation: None.
Activities: None.

Decision Support Services (DSS) Code Legend
Green  = No weather impacts that require action.
Blue   = Long-fused watch, warning, or advisory in effect or
         high visibility event.
Yellow = Heightened impacts with short-fused watch, warning
         or 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 of severe and/or
         direct tropical threats; Events of National Significance.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  54  80  56  82 /   0   0   0   0
BTR  56  81  57  83 /   0   0   0   0
ASD  55  81  58  83 /   0   0   0   0
MSY  64  81  65  82 /   0   0   0   0
GPT  58  81  61  83 /   0   0   0   0
PQL  56  81  57  83 /   0   0   0   0

&&

.LIX Watches/Warnings/Advisories...
LA...None.
GM...None.
MS...None.
GM...None.
&&

$$



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