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

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423
FXUS64 KLIX 130550
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
1150 PM CST Thu Dec 12 2019

.AVIATION...

All terminals currently with IFR ceilings. Rain has moved away
from the area. Potential for conditions to deteriorate further in
the 11-14z time frame before drying begins to lift ceilings to
MVFR. Western terminals...KMCB and KBTR could return to VFR for
several hours during late afternoon. Beyond main TAF period toward
12z Saturday, could see radiation fog form if evening clearing
occurs. 35

&&

.PREV DISCUSSION... /issued 349 PM CST Thu Dec 12 2019/

SHORT TERM...The vast majority of the forecast area will remain
on the northern and western side of a deepening low pressure
system over the coastal waters tonight and tomorrow. This will
keep a northeast wind and a shallow low level cold pool in place
through the overnight and morning hours. Just above the cold pool,
strong southwest flow will continue to pump in a warm and moist
airmass. Strong isentropic forcing over the cold pool in the low
levels will keep overcast skies and light rain over most of the
forecast area tonight. The far western zones along the Atchafalaya
River will see weaker isentropic forcing through the night, and
expect less cloud cover and little to no rain in these areas
tonight and tomorrow morning. Stratus build down is also expected
to occur through the night, and this will lead to some fog
formation across the area. Dense fog is not expected, but
visibilities of around one mile will be possible late tonight and
early tomorrow morning. Temperatures will be little changed from
current readings through the night given the cloud cover in place.

The low will begin to quickly pull away from the area tomorrow
afternoon, but an upper level trough axis will be moving through.
This will will result in continued cloud cover through much of
the day. At best, there could be some clearing over the western
third of the forecast area tomorrow afternoon as the trough axis
gradually shifts to the east. The biggest change by tomorrow will
be a return to more normal temperatures in the middle 60s as
warmer air begins to advect in from the west.

Strong negative vorticity advection and increasing subsidence
throughout the column will result in a sunnier and warmer weekend.
However, there will be the risk of some radiation fog forming
Friday night as the surface high builds in. Temperatures will
rebound back to more normal levels over the weekend with highs in
the upper 60s and lower 70s and lows in the upper 40s and lower
50s.

LONG TERM...A broad positively tilted trough will begin to
deepen over the central CONUS on Monday, and this will result in a
strong surface low forming in the Midwest. An attendant cold
front will sweep into the forecast area Monday night then push
through the coastal waters and into the central Gulf of Mexico on
Tuesday. At this time, instability looks sufficient to allow for
thunderstorm development. However, the strongest dynamics will be
displaced well north of the forecast area. At this time, the risk
of severe thunderstorm development looks to be minimal at best. If
any area saw severe thunderstorms form, it would be across
portions of Southwest Mississippi. Temperatures will warm into the
middle and upper 70s Monday afternoon in advance of the
approaching front.

The risk of thunderstorms will diminish late Monday night as the
front pushes well offshore. However, a general southwest flow
pattern aloft will allow for post-frontal cloud cover and shower
activity into Tuesday morning. These clouds and showers are
expected to come to an end by the afternoon hours on Tuesday as
the main trough axis slides through and a increasingly drier and
colder airmass advects in from the north. By Tuesday night, clear
skies and much colder temperatures are expected across the area.
These clear and cold temperatures will persist through Thursday. A
light freeze will be possible both Tuesday and Wednesday nights
for most of the area. Only areas along the immediate Louisiana
coast and south of Lake Pontchartrain are forecast to remain just
above freezing in the middle to upper 30s.

AVIATION...A low stratus will continue to build down through the
evening hours. Expect to see prevailing IFR conditions at nearly
all of the terminals this evening with a further build down into
LIFR and VLIFR conditions after 08z. Isentropic forcing will also
support the development of light rain overnight, and this combined
with fog will produce reduced visibilities of between one half and
one mile late tonight. Conditions should begin to gradually
improve after 15z, but prevailing IFR restrictions can be expected
through 18-21z. After 21z, conditions should begin to improve into
MVFR range at all of the terminals and ceilings rise above 1000
feet.

MARINE...Conditions will gradually improve through the night over
the coastal waters and expect to see a lighter northwest wind of
10 to 15 knots in place by tomorrow afternoon. Seas will also
gradually decrease from 4 to 7 feet this evening to around 2 to 4
feet by tomorrow afternoon. As a surface high settles in on
Saturday, lighter and more variable winds of 5 to 10 knots and
seas of 1 to 2 feet are expected. The surface high will pull to
the east of the waters on Sunday and increasing southerly flow is
expected to develop. Winds will rise to around 15 knots in the
Gulf water and around 10 knots in the sounds and lakes by Sunday
afternoon. Seas will also increase to around 3 to 5 feet on the
back of these winds. A strong cold front is expected to push
through the waters Monday night. Strong northerly winds of 20 to
30 knots will develop over all of the waters by Tuesday morning
resulting in another round of small craft advisory conditions.

DECISION SUPPORT...

DSS code: Blue.
Deployed: None.
Activation: None.
Activities: Forecast Support for the City of New Orleans.

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; Marginal risk severe or excessive rain.
Yellow = Heightened impacts with short-fused watch, warning or
         advisory issuances; radar support for slight risk severe
         or excessive rain.
Orange = High Impacts; Enhanced risk severe; nearby tropical events;
         HazMat or other large episodes.
Red =    Full engagement for Moderate to high risk of severe and/or
         excessive rainfall, or direct tropical threats; Events of
         National Significance.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  47  65  47  68 /  40  20   0   0
BTR  48  67  48  69 /  30  10   0   0
ASD  47  67  48  69 /  70  20  10   0
MSY  53  66  53  68 /  70  10   0   0
GPT  49  64  49  66 /  70  40  10   0
PQL  48  67  48  69 /  70  50  20   0

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Small Craft Advisory until 3 AM CST Friday for GMZ575-577.

MS...None.
GM...Small Craft Advisory until 3 AM CST Friday for GMZ577.

&&

$$



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