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

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047
FXUS64 KLIX 151335
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
735 AM CST Fri Dec 15 2017

.SOUNDING DISCUSSION...

Routine flight terminated about 10 miles east of Mobile at a
height of 110,000 feet, or 20.8 miles above the surface.

Airmass has moistened since last night with a precipitable water
value of 0.85 inches, but most of the moisture is located above
700 mb, with a saturated or nearly saturated layer between 650 and
350 mb. This fits with the solid high and mid level cloud cover
observed at launch. Frontal inversion looked to be just below 925
mb at launch time. Freezing level this morning is at 9,600 feet
with the -20C level at 22,700 feet.

Northerly winds at the surface up to just below 925 mb, with
westerly winds for the remainder of the flight. Max wind of 121
knots was reported near 34,000 feet. 35

&&

.PREV DISCUSSION... /issued 357 AM CST Fri Dec 15 2017/

SHORT TERM...
An upper trough will be swinging across the Mississippi Valley
this morning. At the surface, observations show a cold front
currently moving southward across the CWA. At the same time, the
sub-tropical jet is carrying Pacific moisture across Mexico to the
northern Gulf coast. Showers will develop over portions of the
forecast area as a result of this overrunning moisture. The bulk
of rain will be limited to areas from New Orleans southward.
Exactly how far north the showers actually reach is quite
challenging. Thinking it will be around I-12. In terms of
temperatures, the combination of overcast skies and cold air
advection will likely keep temps fairly steady throughout the day.

These showers will fade and shift south as the front continues
towards the central Gulf of Mexico. Decreasing clouds and colder dry
air mass moving in will bring down nighttime lows quite a bit.
Expecting mid 30s for most locations with a few in Mississippi
touching the freezing mark Saturday morning.

LONG TERM...
Models still show a cutoff low that is currently stuck over the Baja
of California getting pickup by a Pacific trough and racing
northeast to the mid Mississippi Valley this weekend. In response
to this, a surface low and appendant frontal boundary will
develop over east Texas, with the front stalling over the CWA
Sunday. Numerous showers and a few thunderstorms are likely to
develop as frontogenesis takes place. While rain will begin from
west to east Saturday night, most of the higher pops shouldn`t
come in until Sunday.

The boundary will likely remain stalled along the northern Gulf
Coast through Tuesday as troughing is maintained west of the CWA.
This will lead to bouts of rain moving across the area rather than
constant downpours. Confidence in the forecast is normal through
this period and below normal thereafter.  The main difference is the
the GFS clears out moisture Wed and Thu with the aforementioned
Pacific trough, while the ECMWF is slower with the progression of
this trough. Didn`t make too many changes from previous forecast
and went with a blend of solutions for pops.

MEFFER

AVIATION...VFR conditions will generally prevail through the TAF
forecast period with primarily mid and high level clouds expected. A
cold front will push south across the forecast area overnight/early
Friday morning. Some patchy fog may occur prior to the frontal
passage at KGPT and KHUM. Otherwise, a few showers may impact the
more coastal Louisiana TAF sites Friday morning. 11

MARINE...Cold front quickly moving through and winds will pick up
later this morning. Winds over all of the open waters will increase
to at least 15-20 kts but the outer waters south and west of the
delta will likely be closer to 20 kts with higher gusts. With that
will hoist an SCY for those waters and then an SCS for the rest of
the open waters just for today. High pressure will quickly slide
towards the southeastern CONUS and winds will relax some Friday
night and begin to shift out of the east through Saturday. By
Saturday evening and into Sunday with high pressure still off to the
east and lower pressure developing along the TX coast winds will
begin to slowly increase and become onshore. As the low pulls away
to the northeast the front will become stationary over the area with
winds relaxing again. /CAB/

.DECISION SUPPORT...

DSS code: Blue.
Deployed: None.
Activation: None.
Activities: Small Craft Advisory

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  49  31  55  49 /  10   0  10  20
BTR  50  35  57  53 /  20   0  10  20
ASD  52  35  57  53 /  40  10  10  20
MSY  53  40  58  55 /  60  10  10  20
GPT  52  37  56  54 /  30  10  10  20
PQL  52  31  57  51 /  20  10  10  10

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Small Craft Advisory until 6 PM CST this evening for GMZ570-572-
     575.

MS...None.
GM...Small Craft Advisory until 6 PM CST this evening for GMZ572-575.

&&

$$



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