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

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000
FXUS64 KLIX 030529
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
1129 PM CST Fri Dec 2 2016

.AVIATION...
Any persistent light to moderate rain could lead to MVFR
conditions (CIGS 2500-3000 feet and VSBYS 3-5 nm) at times later
tonight, mainly for the airports west of I-55, otherwise mostly
VFR conditions will prevail through Saturday afternoon. There is
expected to be more widespread MVFR conditions developing Saturday
evening. Easterly winds are expected to rise with gusts over 20
knots likely by mid morning Saturday. 22/TD

&&

.PREV DISCUSSION... /issued 826 PM CST Fri Dec 2 2016/

UPDATE...
00z LIX sounding has moistened up quite a bit above 8000 feet
while the low levels remained rather dry. The precipitable water
increased from a half inch at 6 am this morning to one inch this
evening, and the LCH sounding increased from a half inch to 1.37"
during the same time. Top down moistening from over-running
rainfall was occurring and will continue tonight, and
observations in western sections have reported sprinkles to
measurable light rainfall (trace amounts to .01") as of 745 pm.
Based on the high coverage of stratiform rainfall, radar and
satellite trends, and synoptic and high-res model trends, have
raised the probability of precipitation into the likely to
categorical range (60-100%) tonight where it is raining or likely
to rain based on forecast QPF. It is very possible another update
to expand the 80-100% rain chance area tonight could be needed
if rain continues in areas where the surface temperature/dewpoint
spreads continue to decrease. 22/TD

MARINE...
Extended the Small Craft Advisory (SCA) in time into Saturday
night and Sunday morning based on forecast conditions and latest
wind and wave guidance and forecasts. SCA conditions are expanding
over the coastal waters and will likely develop over the sounds
later this evening or after midnight. 22/TD

DECISION SUPPORT...
DSS code: Blue.
Deployed: None.
Activation: None.
Activities: Small Craft Advisory.
            Monitoring heavy rainfall potential Sunday into
            Monday and severe thunderstorm potential Monday.

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.

PREV DISCUSSION... /issued 337 PM CST Fri Dec 2 2016/

DISCUSSION...
Period of active weather will begin tomorrow as a slow moving
frontal system affects the Gulf South. Upper trough currently
digging into the desert southwest is expected to close off
tomorrow morning, slowing its forward progression as it nearly
becomes cut off from the overall flow.

At the same time, a surface low is expected to develop over
southeast Texas. Flow around this low will force a warm front
toward the northern gulf coast. Should see light rain begin to
spread across the area beginning late tonight and tomorrow, and in
fact we`re already seeing returns just southwest of the
Atchafalaya River mouth.

Warm front should be right along the coast by Sunday morning with
additional overrunning rainfall spreading across the area. Right
now it looks like the heaviest rain totals should remain just to
the west and northwest of the local area, but it should be noted
that if everything shifts slightly eastward, heavier rain could
sneak into southeast LA and southern MS, mainly west of I-55. For
the time being, WPC is indicating a marginal risk of excessive
rainfall locally with a slight risk a bit farther west.

By Monday the upper low will begin to open up and lift toward the
northeast, taking the surface low northeastward along with it. As
it does so, the upper trough is forecast to take on a slightly
negative tilt. This would tend to support at least some threat of
severe weather, and in fact SPC does include much of the area in a
15% risk area. The severe weather threat area will be greatest
along and to the south of the warm front - in the so-called warm
sector. It remains to be seen how far inland the warm front will
penetrate before surface low and cold front move through. Right
now, the area of greatest risk appears to be southeast Louisiana
and coastal Mississippi, but the severe weather threat will
continue to be refined over the coming days. Latest forecast
soundings continue to indicate that if any severe thunderstorms do
develop, all modes of severe weather would be possible.

The cold front should sweep through the area Monday evening and
into Monday night, ushering in some cooler temperatures for mid
week. A secondary, reinforcing front is forecast to move through
the area with maybe a few scattered showers right along the front.
This secondary surge could bring a blast of much colder air, but
there are still some discrepancies between the different models
concerning just how cold.

AVIATION...
VFR conditions expected through the night. As isentropic lift
strengthens, ceilings will lower with MVFR conditions developing
during the afternoon hours Saturday.

MARINE...
Will keep headlines as currently configured. High over the Ohio
River Valley and low developing over south Texas has tightened the
pressure gradient. 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 will be late next week. 35/CAB

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  47  55  52  66 /  70  80  70  80
BTR  49  59  58  69 / 100  70  60  80
ASD  50  63  60  72 /  50  50  60  80
MSY  57  67  64  75 /  70  40  60  80
GPT  52  63  60  70 /  30  30  60  80
PQL  49  63  58  72 /  20  20  50  80

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Small Craft Advisory until midnight CST Saturday night for
     GMZ532-536-538-550-552.

     Small Craft Advisory until 9 AM CST Sunday for GMZ555-557-570-
     572-575-577.

MS...None.
GM...Small Craft Advisory until midnight CST Saturday night for
     GMZ536-538-550-552.

     Small Craft Advisory until 9 AM CST Sunday for GMZ557-570-572-
     575-577.

&&

$$



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