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

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000
FXUS64 KLIX 021302
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
702 AM CST Fri Dec 2 2016

...SOUNDING DISCUSSION...

A stable and unusually dry airmass is lingering over the region as
a zone of high pressure moves towards the Southeast. The
precipitable water value is up to near a half an inch, primarily
due to clouds between 8000 and 11000 feet, as atmospheric moisture
begins to overspread the area ahead of the next upper level
trough. Temperature inversions exist once again between the
surface and 6000 feet with an elevated inversion at the top of the
aforementioned clouds. Winds were from the east-northeast in the
low levels and then back and blow generally from the west-
southwest from 10000 feet to the tropopause. A peak wind speed of
102 knots was at 39600 feet.

12z balloon info: A routine flight ascending for 105a minutes
reaching a height of 20.2 miles above the ground bursting over
near Grand Bay, AL 90 miles downrange from the office.

Ansorge

&&

.PREV DISCUSSION... /issued 412 AM CST Fri Dec 2 2016/

SYNOPSIS...
Latest surface analysis showed an expansive area of high pressure
from the Northern Plains to the Lower Mississippi Valley with a
1023 millibar high over Mississippi. Upper air analysis revealed a
trough axis from Montana to northern Arizona and fast- moving
southwest flow from southwest United States to Atlantic seaboard.
Isotach analysis at 250 millibar revealed a jet maximum of 160
knots on the back side of the trough along the west coast of
British Columbia and Washington. 18

SHORT TERM...
Jet maximum will dive south and develop the trough into a closed
low just south of Arizona late tonight. This will cause the west
to southwest flow aloft to develop to a broad ridge over
southeast and south central United States today and tonight. As a
result, heights will increase and support a slight warming trend
into the weekend.

Main surface high pressure is expected to shift eastward and low
level winds will begin to turn more easterly and then
southeasterly Saturday and Sunday. This will bring in moisture.
At the same time, the newly closed low will slowly track
east southeast over Mexico. Approaching upper level low and
southwest flow over Rockies in Mexico will develop a lee trough
over lower Texas coast Saturday into Sunday. The surface trough
axis will expand east into a warm front along the Texas and
Louisiana late Saturday into Sunday. Continuous moist southwest
flow ahead of closed low will allow precip to break out late
tonight across west zones and continue over the forecast area into
the weekend. 18

LONG TERM...
By Monday, a surface low will develop along the Texas coast. This
low will track northeast placing our forecast area in the warm
sector Monday afternoon and evening. This will result in an
increase in instability and the potential for additional
thunderstorms before a cold front sweeps through the area Monday
evening or Monday night.

Aloft, the closed low over Mexico is expected to open and become
negatively tilted over east Texas on Monday. There is still some
disagreement between the different models concerning the timing of
the trough passage over northern Louisiana and northern
Mississippi. Euro is still a bit faster and slightly stronger vort
max than the GFS. Both model solutions create a pattern conducive
for strong to severe surface base storms in the warm sector over
the forecast area on Monday.

SPC continue to include a 15% severe weather risk area for Monday
and Monday night. This risk area currently encompasses all of
southeast Louisiana and southern Mississippi, but will likely be
refined over the coming days and may shift in both area and time.
At this time it appears IF severe storms do develop, all modes of
severe weather would be possible.

The associated cold front will sweep through the area Monday
evening or Monday night and we should see a brief lull in the rain
chances Tuesday/Tuesday night before a reinforcing front brings
another shot of rain through the area Wednesday. With little
moisture to work with, however, we should only see isolated to
scattered activity right along the front on Wednesday and have
maintained low end chance POPs. Behind this second front, we
could be in for a blast of colder air with temperatures well below
normal for the end of next week. 18

AVIATION...
VFR conditions should persist through today but after 00z things
should begin to slowly change especially west of I-55. After 06z
low clouds should begin to push in impacting BTR and MCB but rain
should hold off until after 12z. /CAB/

MARINE...
High pressure has built into the Lower MS Valley already and will
continue to slide to the east. At the same time an area of low
pressure will develop over Mexico and southern TX with the trough
axis extending northeast along the TX coast. This is already and
will continue to tighten the pressure gradient eventually leading
to strong easterly winds across much of the coastal waters. Will
go ahead and begin the exercise caution headlines now over all
zones with SCY conditions expected to begin around sunrise in the
outer waters, especially west of the mouth of the river. The
easterly winds should increase to near 20 knots over all of the
open waters and MS Sound by late this afternoon or this evening.
These zones will then go into the SCY for tonight.

Low pressure will continue to deepen over Mexico/southern TX through
Sat. With that the adv will likely need to be extended through Sat
and possibly into Sun as the pressure gradient remains tight. The
sfc low is finally expected to lift through the region Mon at which
then winds should shift to westerly and relax. Next major cold front
could be late next week. /CAB/

DECISION SUPPORT...

DSS code: Blue.
Deployed: None.
Activation: None.
Activities: Hazardous Marine Conditions.

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  64  45  55  50 /  10  50  70  60
BTR  64  48  60  54 /  10  60  70  60
ASD  65  51  64  56 /  10  40  50  60
MSY  64  56  69  63 /  10  50  50  60
GPT  65  52  63  59 /   0  20  30  60
PQL  65  50  63  54 /   0  10  30  60

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Small Craft Advisory from 6 PM this evening to 6 AM CST Saturday
     for GMZ532-536-538-550-552-555-557.

     Small Craft Advisory until 6 AM CST Saturday for GMZ570-572-575-
     577.

MS...None.
GM...Small Craft Advisory from 6 PM this evening to 6 AM CST Saturday
     for GMZ536-538-550-552-555-557.

     Small Craft Advisory until 6 AM CST Saturday for GMZ572-575-577.

&&

$$



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