River Flood Warning 66, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
651 PM CDT Fri Apr 7 2023

...New AVIATION...

.SHORT TERM...
(This evening through Saturday night)
Issued at 254 PM CDT Fri Apr 7 2023

Water vapor imagery analysis shows a very vigorous upper level
trough and split jet dynamics ejecting out of the Lower Rio
Grande Valley towards the Lower Mississippi Valley and northern
Gulf coast region this afternoon. These strong upper level
dynamics will interact with a slow moving frontal boundary
currently draped from near Slidell to near Galliano. This boundary
will serve as focusing mechanism for additional convective
development across coastal Louisiana and coastal Mississippi,
including much of metro New Orleans later this evening and through
the overnight hours. Above average precipitable water values will
be supportive of locally heavy rainfall rates, and the flood
watch for flash flooding remains in effect for much of the
forecast area through tomorrow morning. Have categorical PoP in
the forecast to reflect the expected convective development
tonight into early tomorrow morning for coastal areas of the CWA.
Temperatures will be near to slightly warmer than average as cloud
cover inhibits cooling and cold air advection is expected to be
limited.

Saturday will be a day of transition as the strong upper level
trough pushes east of the area, and the frontal boundary begins to
move offshore. Lingering scattered shower and thunderstorm
activity along the coast of Mississippi and in extreme coastal
Louisiana in the morning will move offshore in the afternoon. In
fact, mainly dry conditions beneath an overcast sky is expected
during the afternoon and evening hours tomorrow. Weak cold air
advection and a lack of strong solar insolation will keep
temperatures cooler than average with highs only warming into the
upper 60s and lower 70s. The overcast conditions will continue
into Saturday night as low level moisture remains trapped beneath
a temperature inversion a few hundred feet off the surface, and
temperatures will cool back into the upper 50s and lower 60s.
Despite the overcast skies, very dry air in the mid-levels will
inhibit any rain from forming Sunday night over land based zones.
The offshore waters could see some isolated shower activity
persist.

&&

.LONG TERM...
(Sunday through Thursday night)
Issued at 254 PM CDT Fri Apr 7 2023

Seasonably cooler weather will be prevalent through much of next
week with drier conditions on Sunday into Monday before rain chances
begin creeping up midweek. The weak shortwave aiding convective
activity currently across the area will move off the southeast CONUS
on Sunday and begin phasing with the northern stream trough. This
coupled with amplifying ridging across the central CONUS will
amplify troughiness across the southeast CONUS and aid the CAD-
driven backdoor cold front in reaching the Gulf coast Sunday night
which will supply another glancing shot of cooler air into the
forecast area.

By Monday, a strong deep-layer ridge will amplify across the
northern Rockies causing the weak shortwave trough on the leading
edge to cut off and deepen as it approaches the northwestern Gulf of
Mexico and southern MS River Valley on Tuesday morning. The
interaction with this cut-off low and decaying frontal boundary
situated in the central Gulf will initiate development of a surface
low later Tuesday. Diffluent flow aloft and falling heights focused
across the northern semicircle of the surface low will enhance
widespread convective activity that could be placed offshore
(southern track solutions) or across southeast LA and coastal MS
(northern track solutions) Wednesday and Thursday. Global model
guidance agrees that the general track of the surface flow will
follow the surface pressure falls in the exit region of the cut-off
low northeastward toward the northern or northeastern Gulf by
Thursday. However, the uncertainty in the exact track of the surface
low makes for a difficult precipitation forecast during the middle
of next week. For now, PoPs have been increased to account for
increased confidence in this feature developing and favorable upper
dynamics for elevated convective activity across the northern
portion of the system.

Concerning the nature of this surface low: This surface low will be
developing via baroclinic processes in a highly sheared and colder,
drier atmospheric environment which is not favorable for development
or transitioning of this system into a tropical cyclone. Regardless
of the nomenclature, periods of heavy rainfall could occur with
outer bands of this low and elevated easterly winds gusting 20-25
knots. Elevated winds offshore will provide a large fetch of higher
seas as well which will increase coastal flooding concerns (See
Marine Discussion).

&&

.AVIATION...
(00Z TAFS)
Issued at 645 PM CDT Fri Apr 7 2023
Generally MVFR to IFR conditions will continue for the terminals
through the whole forecast period. Low ceilings will be the
primary concern with ceilings as low as 300 to 700 feet possible.
Showers and thunderstorms are expected late tonight into early
tomorrow which could also impact visibility as well. Storms will
start to clear out around 16 to 18z and ceilings will improve
although will remain in the MVFR to IFR range. -BL

&&

.MARINE...
Issued at 254 PM CDT Fri Apr 7 2023

The primary forecast concern will the development of a broad area
of low pressure in the northern Gulf of Mexico next week. This low
will form as a strong upper level low moves into the Gulf and
sparks low level cyclogenesis in a region of enhanced
baroclinicity along a stalled frontal boundary. This baroclinic
low pressure system will produce strong easterly winds of 20 to 25
knots over the coastal waters as early Sunday, and these winds
are expected to persist through Wednesday before gradually easing
on Thursday. The persistent nature of these winds will combine
with a fairly long fetch from the eastern Gulf to produce high
seas of 8 to 14 feet over the eastern coastal waters next week.
This pattern will lead to coastal flooding concerns next week for
the tidal lakes and coast line east of the Mississippi River in
southeast Louisiana and coastal Mississippi.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  58  70  54  68 /  70  40   0   0
BTR  61  72  60  72 /  70  30   0  10
ASD  63  73  58  71 /  80  60  10  10
MSY  66  72  61  70 /  80  60  10  10
GPT  65  71  58  70 /  80  70  10  10
PQL  64  73  56  70 /  80  70  20  10

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Flood Watch through Saturday morning for LAZ034>037-039-046>048-
     056>060-064>071-076>090.

GM...None.
MS...Flood Watch through Saturday morning for MSZ068>071-077-083-086.

GM...None.
&&

SHORT TERM...PG
LONG TERM....TJS
AVIATION...BL
MARINE...PG

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Special Weather Statement
National Weather Service New Orleans LA
712 PM CDT Fri Apr 7 2023

LAZ070-080045-
Lower St. Bernard LA-
712 PM CDT Fri Apr 7 2023

...Strong thunderstorm capable of producing waterspouts moving into
marshy areas of far eastern St. Bernard Parish through 745 PM CDT...

At 709 PM CDT, Doppler radar was tracking a strong thunderstorm
capable of producing a waterspout over Lake Borgne 12 miles
southeast of Lake Catherine, or 19 miles southwest of Waveland,
moving southeast at 10 mph.

HAZARD...Waterspouts and winds in excess of 30 mph.

SOURCE...Radar indicated.

IMPACT...Waterspouts can easily overturn boats and create locally
         hazardous conditions. Gusty winds could knock down tree
         limbs and blow around unsecured objects.

This storm will remain over mainly rural areas of northeastern St.
Bernard Parish.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Boaters in the area should seek safe harbor.

&&

LAT...LON 3000 8956 3008 8948 2997 8938 2989 8949
TIME...MOT...LOC 0009Z 333DEG 9KT 3004 8952

WATERSPOUT...POSSIBLE
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...30 MPH

95/DM

Special Weather Statement
National Weather Service New Orleans LA
751 PM CDT Fri Apr 7 2023

LAZ070-080130-
Lower St. Bernard LA-
751 PM CDT Fri Apr 7 2023

...A strong thunderstorm capable of producing waterspouts will
affect marshy ares of far eastern St. Bernard Parish through 830 PM
CDT...

At 749 PM CDT, Doppler radar was tracking a strong thunderstorm
capable of producing a waterspouts over the marshy areas of far
eastern St. Bernard Parish. The storm was located 11 miles northeast
of Shell Beach, or 23 miles south of Waveland, moving southeast at 5
mph.

HAZARD...Waterspouts and winds in excess of 25 mph.

SOURCE...Radar indicated.

IMPACT...Waterspouts can easily overturn boats and create locally
         hazardous conditions. Gusty winds could knock down tree
         limbs and blow around unsecured objects.

This storm will remain over mainly rural areas of northeastern St.
Bernard Parish.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Any boaters in the area should seek safe harbor.

&&

LAT...LON 2999 8959 3004 8949 2988 8939 2983 8953
TIME...MOT...LOC 0049Z 332DEG 5KT 2996 8952

WATERSPOUT...POSSIBLE
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...30 MPH

95/DM