991
FXUS64 KLIX 151749
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
1249 PM CDT Sat Jun 15 2024

...New AVIATION...

.SHORT TERM...
(Today through Sunday night)
Issued at 250 AM CDT Sat Jun 15 2024

A highly subsident airmass associated with deep layer ridging
centered directly over the forecast area will remain in place
today. The end result will be very warm and dry conditions
continuing with little in the way of cloud development anticipated
even during peak heating hours. Temperatures will once again
climb into the mid to upper 90s and heat index values will rise to
between 100 and 105 degrees this afternoon.

Tonight and Sunday will be a period of transition from the dry
pattern in place the past few days to a much wetter period of
weather expected for much of the upcoming week. This will be due
to a flux of deep layer tropical moisture currently parked over
the southern and eastern Gulf sliding to the northwest on the
western periphery of the deep layer ridge axis that will remain
centered over the Southeast CONUS. Tonight will remain dry
through the evening hours, but gradually increasing moisture in
the low levels will result in scattered showers and few weak
thunderstorms pushing onshore by daybreak tomorrow. Further
inland, the airmass will remain sufficiently dry and stable to
keep rain shower activity at a minimum. This is well reflected by
an expected PWAT gradient ranging from around 1.4 inches in
southwest Mississippi to near 2 inches along the immediate coast
of Louisiana by daybreak on Sunday.

As the deep layer moisture continues to feed into the region on
Sunday, PWATS will further increase to around 2 inches over the
northern third of the CWA to around 2.3 inches along the Louisiana
coast. These values are between the 90th and max PWAT readings
typically seen in mid-June. Rainfall rates of 2 to 3 inches per
hour can be expected by the afternoon hours, but storm motions of
around 20 mph will help to limit rainfall totals a bit. Still,
there will be a localized street flooding concern for areas with
poor drainage capacity. Despite the very moist airmass in place,
some lingering dry air in the mid- levels could become entrained
into the deepest convection Sunday afternoon. Thus, there could be
some stronger gusts of wind that occur with the most potent
convective cells that form. This is supported by both fairly steep
low level lapse rates in excess of 6.5 C/km and downdraft CAPE
values of around 1000 J/KG.

Conditions will remain unsettled Sunday night as a weak upper
level vorticity maxima sliding up from the central Gulf taps into
the very moist airmass in place. Despite some loss of instability
as temperatures cool into the low to mid 70s, the slight increase
in upper level lift will allow for continued development of
thunderstorms offshore where the diurnal maximum will be reached.
Mean storm motion will be onshore from the south-southeast at
around 20 mph, and this will push these offshore storms inland as
far north as the I-10 corridor through the night. Rainfall
processes will be highly efficient at this point as any mid-level
dry air is flushed out and temperatures start to warm aloft and
would not be shocked to see rainfall rates of 3 to 4 inches per
hour develop during the overnight hours. This will keep the risk
of street flooding in poorly drained areas in place through the
overnight hours. A flood watch for flash flooding will likely be
needed for portions of the forecast area starting Sunday night.

&&

.LONG TERM...
(Monday through Friday)
Issued at 250 AM CDT Sat Jun 15 2024

Monday and Tuesday will see the highest potential for flash
flooding in the CWA as precipitable water values surge to around
2.5 inches across the entire region. H5 temperatures will be quite
warm at -5C, and this will result in highly efficient warm rain
processes continuing Monday into Tuesday. Numerous rounds of
thunderstorms will redevelop over the same areas, and these
thunderstorm complexes will be moving to the northwest at 25 to
30 mph. These storm complexes have the potential to produce
localized rainfall rates as high as 5 inches per hour, and these
high rainfall rates combined with already saturated soils will
lead to excessive runoff into area rivers and drainage canals
resulting in some more widespread flooding concerns beyond the
normal street flooding observed with Summer storms.

The pattern will begin to shift on Wednesday as the plume of
deeper tropical moisture shifts to the west and increased upper
level ridging builds over the area. This increased ridging will
develop in advance of an inverted trough axis pushing westward
from Florida. A sharp moisture gradient is expected to be in place
by the afternoon hours with PWATS ranging from near 2 inches along
the Atchafalaya Basin to around 1.5 inches across coastal
Mississippi. These more average PWAT values will persist into
Thursday night, and the end result will be a return to more
typical convective coverage and normal Summer rainfall rates of 1
to 2 inches per hour. Storm motion will continue to be
northwesterly at 25 to 30 mph, and this will help to limit
rainfall totals. However, the already saturated soils will still
lead to a higher than average flood threat as any rainfall quickly
runs off into the drainage systems. Some localized street
flooding will be a concern, but the more significant flood threat
will be lower on Wednesday and Thursday. Temperatures will also
warm back to more normal readings by Thursday as convective
activity decreases back to the scattered diurnally driven activity
typically seen in June.

The inverted trough axis will finally move through the forecast
area on Friday, and another surge of deeper tropical moisture and
increased convective coverage will take hold of the area. PWATS
are expected to climb back to near 2 inches, and rainfall rates of
2 to 3 inches per hour will be possible with the strongest
thunderstorms that form. Once again, the saturated soils in place
will result in higher than normal runoff and the threat of
localized street flooding concerns. Temperatures will be near
average in the upper 80s and lower 90s as the convection will
still be highly diurnal despite the increased forcing aloft
associated with the inverted trough axis.

&&

.AVIATION...
(18Z TAFS)
Issued at 1245 PM CDT Sat Jun 15 2024

Dry mid-level air will keep VFR conditions and no rain across the
area for the rest of today and into tomorrow. Much more moist air
is expected to advect into the area from the Gulf tomorrow
afternoon. When this happens, expect convective coverage to
increase, mainly at the southern terminals (MSY, NEW, and HUM)
where the moisture is more prevalent. Expect the scattered
convection to continue into the evening as well beyond this TAF
cycle.

&&

.MARINE...
Issued at 250 AM CDT Sat Jun 15 2024

A tightening pressure gradient between a ridge over the Southeast
CONUS and a strengthening area of low pressure in the Bay of
Campeche will result in an extended period of small craft advisory
conditions over the coastal waters during the upcoming week. These
small craft conditions with winds of 20 to 25 knots and frequent
gusts to 30 knots are expected to develop as early as tomorrow
night, but more likely on Monday and then continue through
Thursday. These winds extend across a long fetch from the eastern
Gulf, and this will allow for a decent swell of 2 to 3 feet to
move into the area. This swell will combine with wind waves of 5
to 7 feet to push offshore seas to around 10 feet during the week.
Wave run-up along east and south facing shores will also be an
issue through the week, and some minor coastal flooding is
anticipated to occur during high tide cycles starting on Tuesday
and continuing through Thursday.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  70  91  72  83 /  10  60  50  90
BTR  75  93  75  85 /  10  80  60  90
ASD  75  90  75  85 /  30  80  70  90
MSY  79  90  77  84 /  30  90  80  90
GPT  77  89  77  85 /  30  80  70  90
PQL  75  90  76  86 /  30  80  70  80

&&

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

$$

SHORT TERM...PG
LONG TERM....PG
AVIATION...JZ
MARINE...PG