Special Weather Statement, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
719 PM CST Mon Dec 5 2016

...SOUNDING DISCUSSION...
The sounding is near saturated this evening through a broad
inversion up to 880 mb, which represents the elevated portion of
the warm front. PW of 1.6 inches is well above average for this
time of year and there was localized heavy rain earlier today. The
chance for showers and storms continues this evening, but will be
ending from west to east overnight as much drier air moves in.
Instability is elevated, though there is still 1300 J/KG of most
unstable CAPE present. The primary threat from any storms will be
strong winds, though that is a low chance and mainly for the
eastern portion of the area. Winds are easterly at the sfc then
switch to southwest by 950 mb. Peak wind is 95 kts at 180 mb.

Krautmann

&&

.PREV DISCUSSION... /issued 402 PM CST Mon Dec 5 2016/

SHORT TERM...
Warm front situated along the immediate LA coast and cutting
across Plaquemines Parish near Pointe a la Hache to Mobile Bay at
this time. Surface based air to the south with elevated
instability on 50+kt low level flow over the stable marine layer.
1005mb surface low near Vermilion Bay moving NNE to bring cold
front through the forecast area through the evening hours.
Rainfall has tapered a bit but may re-ignite once low moves inland
a bit and some frontogenetic forcing takes hold with northward
surge of warm air. It does appear dry-slot moves the precipitation
east of the forecast area by midnight. Still have some potential
for severe wind gusts given amount of low level jet dynamics just
above the stable layer, but threat diminishes or ends with frontal
passage between 9 pm and midnight from west to east. Other concern
will be propensity for fog to form when it is not raining as
residual ground moisture and a light low level wind allow for
saturation to dewpoint despite cloud cover, but again, these
conditions should improve with frontal passage and dry air
advection overnight. Tuesday should be dry and cool to mild with
limited cold air advection. Better surge of cooler air takes place
Wenesday and Thursday.

LONG TERM...
Light to moderate freeze conditions expected for a couple of
nights Thursday night and again Friday night for the more interior
and drainage prone areas of the CWA. Air mass shifts east rather
quickly and moderates over the weekend for strong return flow to
onset later Saturday and Sunday. Models showing a deeper surge of
cold air poised to move out of the Plains States middle of next
week. 24/RR

AVIATION...
The broad shield of rain over the area this morning and early
afternoon has dissipated with only scattered showers remaining.
However, IFR and LIFR ceilings ranging from 300 to 1000 feet will
continue to impact the terminals through the reaminder of the night
and into tomorrow morning.  Ceilings should finally mix out and
conditions improve to MVFR and VFR range after 18z tomorrow.  The
low ceilings should also allow for visibilities of 1 to 3 miles
tonight.  HRRR model guidance continues to indicate the potential
for another band of convection developing around 00z and impacting
most of the terminals through 03z.  Have kept in a tempo group with
TSRA wording to reflect this risk.  32

MARINE...
Small craft advisory has already been posted earlier this
afternoon in anticipation of wind increase this evening as
gradient tightens pre-frontal, followed by dry air enhancement
once the system and front moves through overnight. winds should
settle rather quickly Tuesday with little pressure gradient
support. Cold air surge enters north gulf late Wednesday with
colder air pushing off the coast during the day Thursday. This
should be another SCA situation until the cold air advection
abates Friday afternoon. Air mass modifies rather quickly over the
weekend with baroclinic return expected to bring moderate onshore
flow by late Saturday night into Sunday. 24/RR

DECISION SUPPORT...
DSS code: Blue.
Deployed: None.
Activation: None.
Activities: Monitoring convective and heavy rainfall trends through
            tonight.

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  52  62  45  65 /  50   0   0   0
BTR  52  63  47  69 /  40   0   0   0
ASD  53  65  46  68 /  40   0   0   0
MSY  57  64  52  68 /  30   0   0   0
GPT  56  65  48  66 /  40   0   0   0
PQL  56  65  46  66 /  40   0   0   0

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Small Craft Advisory until 9 AM CST Tuesday for GMZ530-532-534-
     536-538-550-552-555-557-570-572-575-577.

MS...None.
GM...Small Craft Advisory until 9 AM CST Tuesday for GMZ532-534-536-
     538-550-552-555-557-570-572-575-577.

&&

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE NEW ORLEANS LA
442 PM CST MON DEC 5 2016

LAZ058-060-052315-
ST. CHARLES-ST. JOHN THE BAPTIST-
442 PM CST MON DEC 5 2016

...A STRONG THUNDERSTORM WILL AFFECT NORTHWESTERN ST. CHARLES AND ST.
JOHN THE BAPTIST PARISHES...

AT 442 PM CST...A STRONG THUNDERSTORM WAS LOCATED OVER EDGARD...OR
NEAR RESERVE...MOVING NORTHEAST AT 40 MPH.

LOCATIONS IMPACTED INCLUDE...
RESERVE...LAPLACE...HAHNVILLE...WALLACE...ST. ROSE...KILLONA...NEW
SARPY...GARYVILLE...TAFT...EDGARD...DESTREHAN...NORCO...AMA...
MONTZ...LULING AND BOUTTE.

LAT...LON 3008 9067 3020 9042 3018 9043 3014 9043
      3009 9041 3006 9038 3005 9033 3006 9032
      3006 9031 3005 9029 2991 9028 2991 9064
TIME...MOT...LOC 2242Z 236DEG 36KT 3002 9054

CAB

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE NEW ORLEANS LA
749 PM CST MON DEC 5 2016

LAZ059-061-063-067-068-060215-
UPPER LAFOURCHE-UPPER JEFFERSON-UPPER PLAQUEMINES-LOWER
JEFFERSON-LOWER LAFOURCHE-
749 PM CST MON DEC 5 2016

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SOUTHEASTERN
LAFOURCHE...WESTERN PLAQUEMINES AND CENTRAL JEFFERSON PARISHES...

AT 749 PM CST...RADAR INDICATED STRONG THUNDERSTORMS WERE LOCATED
ALONG A LINE EXTENDING FROM NEAR GALLIANO TO 11 MILES SOUTHWEST OF
LEEVILLE TO 29 MILES SOUTHEAST OF COCODRIE. MOVEMENT WAS NORTHEAST AT
60 MPH.

LOCATIONS IMPACTED INCLUDE...
GALLIANO...CUT OFF...BELLE CHASSE...GOLDEN MEADOW...JEAN LAFITTE...
LEEVILLE...LAFITTE...BARATARIA AND GRAND ISLE CMAN.

TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THESE STORMS...AND MAY
CAUSE LOCALIZED FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH FLOODED
ROADWAYS.

FREQUENT CLOUD TO GROUND LIGHTNING IS OCCURRING WITH THIS STORM.
LIGHTNING CAN STRIKE 10 MILES AWAY FROM A THUNDERSTORM. SEEK A SAFE
SHELTER INSIDE A BUILDING OR VEHICLE.

LAT...LON 2920 9026 2919 9027 2929 9037 2925 9038
      2941 9041 2984 9003 2940 8999 2941 9003
      2928 8993 2936 9007 2934 9004 2926 8995
      2920 9004 2925 8998 2933 9010 2932 9010
      2918 9007 2909 9024
TIME...MOT...LOC 0149Z 210DEG 50KT 2940 9037 2911 9032 2890 9039

11