721
FXUS64 KLIX 112056
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
356 PM CDT Tue Jun 11 2024

...New SHORT TERM, LONG TERM, MARINE...

.SHORT TERM...
(This evening through Wednesday night)
Issued at 242 PM CDT Tue Jun 11 2024

Upper flow generally west northwesterly across the local area.
Northern stream shortwaves over New England, the Canadian Prairie
provinces and British Columbia. A southern stream shortwave was
noted over the Texas/Oklahoma border and a closed low over the
Pacific to the southwest of San Diego. At the surface, a frontal
boundary was noted south of Lake Pontchartrain, generally south of
the Interstate 10 corridor. Quite a spread in moisture values
either side of the front, with precipitable water values as high
as 2 inches south of the boundary as noted on the 12z LCH
sounding, and as dry as 1 inch on the JAN sounding. Our sounding
weighed in at 1.82 inches. Scattered thunderstorms were noted on
satellite and radar near the front over the Louisiana coastal
parishes this afternoon extending from about Morgan City to Port
Sulphur. These storms weren`t moving much, so there will be a few
locations getting very heavy rain, with most areas dry.
Temperatures at 3 PM CDT away from thunderstorms were generally in
the upper 80s and lower 90s, but dew points ranged from the lower
60s well north of the front over southwest Mississippi to mid 70s
near the Louisiana coastline.

Expect convection to slowly dissipate with the loss of surface
heating around sunset. Forecast soundings indicate some continued
drying on Wednesday with precipitable water values dropping about
another quarter inch in the New Orleans area. Convective
development on Wednesday is likely to be limited to the Louisiana
coastal parishes again, and the 20-30 percent PoPs may even be
overstating coverage. Again, timing of development will be
diurnally driven, mainly in the 18z Wednesday-00z Thursday window.

Expect overnight lows tonight and tomorrow night to be several
degrees cooler than this morning, but probably not quite as cool
as the NAM/MET numbers. Today`s highs away from convection are
probably a good starting point, and possibly a degree or two
warmer with the lower moisture content.

&&

.LONG TERM...
(Thursday through Monday night)
Issued at 242 PM CDT Tue Jun 11 2024

The long term portion of the forecast is essentially split into
two parts. Thursday through Saturday night is a fairly high
confidence portion of the forecast, with confidence in details
falling rather quickly beyond that point.

Upper ridging near El Paso on Wednesday will build eastward to
near Memphis by Saturday, to the Carolinas on Monday. This will
gradually turn the upper flow along the northern Gulf Coast
easterly by the end of the weekend. The main uncertainty is where
an impulse moving through the easterlies heads northward around
the west side of the ridge, pulling deeper moisture northward with
it.

For Thursday through Saturday, rather dry air will be in place,
with precipitable water values near the 10th to 25th percentile
climatologically, generally near or below 1.25 inches. This
should mean little to no precipitation development, and forecast
soundings show low level temperatures supportive of at least mid
to upper 90s in much of the area. The deterministic NBM values
even show a few spots topping out right at 100 degrees on
Saturday, especially if a sea breeze doesn`t generate.

As the upper ridge axis shifts east of the area Saturday night and
Sunday, deep southeasterly flow plugs in, with moisture increasing
rapidly as noted by precipitable water values climbing above 2
inches Sunday night on GFS forecast soundings. We`d note that
there`s been quite a bit of spread between the GFS and ECMWF camps
regarding precipitation from Sunday onward with last night`s runs
ranging from almost certain rain on the GFS to almost no rain on
the ECMWF operational, with it`s focus well to the west. Today,
the GFS solution has drifted somewhat toward the ECMWF, with
somewhat lower PoPs and QPF. There`s no question that there will
be very heavy rainfall "somewhere" along the northern Gulf Coast
Monday and Tuesday, but right now, pinpointing the location is a
low confidence forecast.

With uncertainty regarding precipitation chances/amounts, it goes
without saying that temperatures will also be uncertain, with
about a 10 degree F range for Sunday/Monday in the ensemble
guidance highs.

&&

.AVIATION...
(18Z TAFS)
Issued at 1252 PM CDT Tue Jun 11 2024

At issuance time, cumulus had started developing over the previous
hour, with convective echoes detected near a Thibodaux to
Boothville line. With movement to the west and southwest, this
should limit TSRA to the KHUM terminal area, although the threat
would be non-zero to KNEW and KMSY. Direct impacts, if they occur,
will produce MVFR ceilings and IFR or lower visibilities to KHUM.
Most likely, impacts would be one hour or less, and with the
eventual loss of surface heating, should see dissipation near or
prior to 00z Wednesday. Expect VFR conditions elsewhere through
the forecast period, and during the overnight hours at KHUM.

&&

.MARINE...
Issued at 242 PM CDT Tue Jun 11 2024

In the early portion of the forecast, the only real concern is
thunderstorm potential in the next day or two near the frontal
boundary. By late in the weekend into early next week,
thunderstorms are likely to become more widespread across the
waters. With stronger onshore flow expected, Small Craft Exercise
Caution headlines may be necessary by Sunday or Monday. As this
southeasterly flow become more persistent, swell may build
somewhat, causing higher tide levels. Fortunately, astronomical
tide levels are expected to be fairly narrow over the weekend,
which may limit coastal flooding impacts.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  64  88  64  91 /   0  10   0   0
BTR  70  93  70  96 /  10  20   0   0
ASD  70  93  71  95 /  10  20   0  10
MSY  76  92  77  93 /  10  30   0  10
GPT  70  93  72  94 /  10  10   0  10
PQL  68  95  70  96 /  10  10   0  10

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...None.
MS...None.
GM...None.
&&

$$

SHORT TERM...RW
LONG TERM....RW
AVIATION...RW
MARINE...RW