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

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FXUS64 KLIX 180957

Area Forecast Discussion
National Weather Service New Orleans LA
357 AM CST Sun Nov 18 2018


Surface high centered over the Delmarva area with an axis
southwestward into eastern Texas. This leaves us barely on the
cool side of the high. Upper troughing extends from the Great
Lakes westward into Nevada. Quite a bit of high level moisture
moving through the southern stream of the jet, which was reflected
in a significant amount of high cloud cover yesterday. At present,
the high clouds seem to be limited to areas south of Lake
Pontchartrain. A few locations reporting a little bit of fog/haze,
but the only location reporting significant visibility
restrictions is Pascagoula, which is usually a favored location
for fog. At 3 am, temperatures north of Lake Pontchartrain
remained rather cool, mid 30s to lower 40s. South of the lake,
temperatures were generally in the 40s, with the exception of
far lower Plaquemines and Jefferson Parishes, where Boothville
reported 57 degrees, and Grand Isle was 61.



As upper trough continues to push southward, high level moisture
will continue to increase today with another surge of high cloud
cover expected to arrive this afternoon or evening. Weak cold
front associated with this trough will move through the area
Monday night into Tuesday. Rain chances will increase across the
western half of the area Monday afternoon, and over most of the
area Monday night before tapering off from north to south
Tuesday morning. NAM/GFS much more bullish on this system than the
ECMWF regarding rainfall. Have given some credence to the ECMWF
solution and have undercut GFS/NAM PoPs somewhat. Trended toward
the warmer end of temperature guidance in most cases through
Tuesday. 35



Beyond Tuesday, forecast confidence drops rapidly in quick moving
southern stream flow. First wave arrives Wednesday night into
Thanksgiving Day. ECMWF solution quite a bit wetter than GFS with
GFS keeping most precipitation over the Gulf and far lower
portions of the SE Louisiana coastal parishes. Will trend somewhat
toward the ECMWF solution bringing at least light rain well
northward into the area. We`re not talking an all day downpour,
but much of the area could see about a half inch of rain early
Thursday. A brief break late Thursday into early Friday before
another wave brings a good chance of rain back to the area late
Friday and Friday night. Again, the ECMWF is a wetter solution
than the GFS. Another shot of rain looks to time out to late
Sunday into Monday.

It should be noted that as we get further into the forecast, the
ECMWF is considerably stronger with the individual features than
the GFS from Friday onward. This will need to be monitored, as a
stronger solution would necessitate starting to mention
thunderstorms and associated threats. This would also play havoc
with temperature forecasts. Currently about a 7 to 10 degree
spread on both high and low temperatures Friday through Sunday
with the GFS being on the warmer side. Have trimmed several
degrees from the GFS guidance, but not as cool as the ECMWF. 35



Colder temperatures than expected, mostly clear skies and near calm
winds have resulted in visibility restrictions in patchy fog at
KGPT, KHUM, KMCB, KPQL, KNBG and KGAO, and some MVFR conditions
could also develop at KBTR, KMSY and KHDC through 12-13z. KHUM will
likely see the visibility fluctuate mainly from MVFR to LIFR/very
low IFR/at or below airport minimum through at least 12z and
possibly a bit later. Fog should mostly dissipate between 13-14z and
all airports should remain VFR the remainder of the day. Thickening
higher level clouds tonight should inhibit fog formation, however
MVFR to periodic IFR could occur during the 05-13z period at KHUM.



A dome of surface high pressure will persist through Monday across
the central Gulf coast region. This will result in mostly east to
northeast winds around 10 knots or less and seas 2 feet or less
across all waters through Monday. A cold front is expected to move
southeast and push slowly through the central Gulf coast region and
coastal waters Monday night into Tuesday. Northeast to east winds
are expected to rise into the 10 to 15 knots to around 15 knots
range Tuesday and Tuesday night across the coastal waters
(especially west). Seas over western and southern coastal waters
should rise into the 3 to 4 feet range.

A shortwave trough moving into the western Gulf coast region
Wednesday night will likely develop a wave of low pressure along
the frontal boundary, then this inverted trough of a weak area of
low pressure may persist over the northwest Gulf going through the
latter part of the week. Winds should continue to rise into the 15
to 20 knots range Wednesday night across western waters and
expanding into eastern waters Thursday into Thursday night. If a
stronger low pressure are forms as depicted by the ECMWF, then winds
above 20 knots and Small Craft Advisory conditions would occur.



DSS code: Green.
Deployed: None.
Activation: None.
Activities: River flood warnings for Bogalusa, Pearl River and Red
            River Landing

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.


MCB  68  50  66  48 /   0   0  30  50
BTR  70  51  67  50 /   0   0  40  50
ASD  70  50  70  53 /   0   0  10  40
MSY  69  53  69  55 /   0   0  10  40
GPT  68  50  68  53 /   0   0  10  30
PQL  70  48  69  53 /   0   0  10  30



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