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

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000
FXUS64 KLIX 201736
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
1236 PM CDT Sat Oct 20 2018

.AVIATION...
VFR to occasional MVFR category conditions are expected at the
terminals through the afternoon and into the evening hours as a
cold front makes its way south across the forecast area. Scattered
showers and isolated thunderstorms will be possible through the
early evening. VFR conditions are forecast overnight and into
Sunday. Strong and gusty northerly winds will occur overnight in
the wake of the front at KNEW and KMSY. 11

&&

.PREV DISCUSSION... /issued 845 AM CDT Sat Oct 20 2018/

SOUNDING DISCUSSION (CORRECTED)...

This morning`s balloon launch was successful, but required a
second launch due to erroneous/missing temperature data. Few
changes to note in the vertical profile this morning. First and
foremost, areas of fog developed early this morning, thanks to a
shallow and saturated lower PBL in place. This saturated layer
extended roughly 500ft AGL or around 1000mb. Above this layer
appeared relatively dry all the way to 17.5kft AGL or around
530mb, where mid-level clouds persisted in the wake of an
approaching front to the north. A secondary layer of moisture
existed between 300 and 250mb where the better conveyor belt of
upper-level moisture continued to advect an increasing canopy of
cirrus clouds across the area. The vertical wind profile was
almost entirely unidirectional from the W to WSW from near the
surface to the tropopause, ranging 10-15 knots in the lower to
mid-levels, increasing to 30-40 knots in the upper-levels.

It`ll be an interesting forecast for today, as a surface
front is expected to sweep across the area later this afternoon.
Surface destabilization may be slow to occur in areas that do not
have as much cloud cover (primarily near coastal areas or south of
I-10/12). In these areas, modifying this morning`s sounding and
comparing it to the latest RAP13KM runs show the potential for
building instability, and perhaps some isolated/scattered
thunderstorms developing with frontal forcing support, timed just
around the peak diurnal heating later this afternoon. For areas
further to the NW primarily north of I-10/12, ample cloud cover
will limit instability and thunderstorm chances. Regardless,
expect one last humid day with mostly cloudy skies and increasing
rain/storms followed by a steady cool down after the front passes
later this afternoon. KLG

&

PREV DISCUSSION... /issued 621 AM CDT Sat Oct 20 2018/

SHORT TERM...

Return flow has made a short appearance here in the area with
dewpoints this morning anywhere from the upper 60s to the mid 70s
along the coast. This will allow for fog development this morning
and rain chances in the 30-50 percent range today. By this
afternoon and evening, an approaching cold front will sweep
through the area bringing much cooler and drier weather to the
area. By Sunday, temperatures will struggle to reach 70 for highs,
while low temperatures Sunday night and Monday morning could
reach the upper 40s north and west of the tidal lakes.

LONG TERM...

Things get a little more difficult for the beginning of next week.
The general pattern will be a weakening of upper level ridging
over the area allowing for a series of disturbances and weak fronts
to move near and into the area. There is still a fair amount of
model spread in regards to the timing, track and strength of these
impulses, so relied on general model blends for the time being.

AVIATION...

Areas of fog and low ceilings will linger through 14z
before clearing as a front moves in from the north and atmospheric
bouyancy increases.  Prevailing LIFR conditions are expected at
KMCB, KGPT, KASD, KHDC, and KHUM with a mix of IFR and MVFR
conditions expected at KBTR, KMSY, AND KNEW this morning.  As the
front passes through the area between 18z and 00z, a band of showers
may develop.  PROB30 groups are in place to reflect this risk with
MVFR ceilings and visibilities the main concern as the showers
pass through. After 00z, the front should be clearing the coast of
Louisiana, and VFR conditions will develop at all of the
terminals. Ceilings will gradually lift from around 3000 to 5000
feet and winds will increase from the north. The winds will be
strongest at KMSY and KNEW where increased mixing over the warmer
lake waters will allow stronger boundary layer winds in excess of
15 knots to descend down to the surface.

MARINE...

A strong cold front will sweep through the coastal waters
this afternoon and evening, and a period of small craft conditions
with northerly winds of 20 to 25 knots and rough seas of 5 to 8 feet
should be in place from this evening through tomorrow evening.  The
pressure gradient will briefly decrease over the waters on Monday,
but a series of low pressure systems moving through the central Gulf
of Mexico will push winds back to between 15 and 20 knots by the
middle of next week.  Seas of 4 to 6 feet can be expected as these
stronger winds take hold.  If the low pressure systems next week are
stronger than currently expected, winds and seas could easily rise
back into small craft advisory range.

DECISION SUPPORT...

DSS code: Blue.
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; 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  74  50  67  44 /  50  10   0   0
BTR  77  54  70  47 /  50  10   0   0
ASD  82  55  70  48 /  50  10   0   0
MSY  82  60  70  57 /  50  20   0   0
GPT  81  55  70  51 /  50  10   0   0
PQL  83  54  71  49 /  50  10   0   0

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Small Craft Advisory from 10 PM this evening to midnight CDT
     Sunday night for GMZ550-552-570-572.

     Small Craft Advisory from 10 PM this evening to 7 PM CDT Sunday
     for GMZ555-557-575-577.

     Small Craft Advisory from 10 PM this evening to 1 PM CDT Sunday
     for GMZ530-532-534-536-538.

MS...None.
GM...Small Craft Advisory from 10 PM this evening to midnight CDT
     Sunday night for GMZ552-570-572.

     Small Craft Advisory from 10 PM this evening to 7 PM CDT Sunday
     for GMZ557-575-577.

     Small Craft Advisory from 10 PM this evening to 1 PM CDT Sunday
     for GMZ532-534-536-538.

&&

$$


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