-- Discussion containing changed information from previous version are highlighted. --
078
FXUS64 KLIX 161136
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
636 AM CDT Sun Jun 16 2024

...New AVIATION...

.SHORT TERM...
(Today through Tuesday night)
Issued at 313 AM CDT Sun Jun 16 2024

A surge of deep tropical moisture will feed into the forecast area
today as deep layer southerly flow develops between a strong ridge
axis over the Southeastern CONUS and a broad upper level low
pressure system in the southwest GOMEX. PWATS will rise from
around 1.5 inches this morning to around 2 inches by tonight.
These elevated PWATS ranging near the 90th percentile to daily max
values for mid-June will remain over the forecast area through
Tuesday night as the upper level pattern remains little changed.
Today will see widely scattered showers and thunderstorms develop
during the late morning hours across coastal Louisiana, and this
convection will then spread inland through the afternoon and
evening hours. Rainfall rates of 1 to 2 inches per hour could
accompany the deepest convection this afternoon, but mean storm
motion between 10 and 15 mph should limit the flood threat to only
a few more prone locations like underpasses in urbanized areas.
The increased convective activity and cloud cover will help limit
temperatures to more average readings in the upper 80s and lower
90s. The scattered shower and thunderstorm activity will persist
through the evening hours before turning more isolated as
overnight lows dip into the low to mid 70s and overall instability
wanes.

A series of weak upper level vorticity maxima embedded within the
deep layer southerly flow will pass through the region on Monday
and Tuesday, and this increased upper level lift will support more
widespread convective activity on both Tuesday and Wednesday.
PWATS will remain near daily max values in the 2.25 to 2.4 inch
range, and very efficient rainfall processes are expected to take
place as H5 temperatures warm to around -4C. The result will be
the potential for hourly rainfall rates of 2 to 3 inches per hour
with the deepest convection that forms both days. Fortunately,
storm motion will be quite fast at around 30 mph both days, and
this will help to limit the overall flood potential across the
region. However, the threat of localized street flooding issues in
more urbanized and poorly drained areas will persist on both
Monday and Tuesday. Convective activity will peak from late
morning through the evening hours as temperatures warm into the
80s each day with more isolated to scattered convective coverage
expected at night as lows fall back into the 70s. Given the
overall lower threat of flooding across a much larger area, have
opted to not issue a flood watch for flash flooding at this time.

&&

.LONG TERM...
(Wednesday through Saturday)
Issued at 313 AM CDT Sun Jun 16 2024

Upper level ridging will build back over the area on Wednesday and
remain in place through Thursday. The result will be a sharp
decrease in PWATS to more normal values of around 1.5 to 1.75
inches both days. Overall, a very normal Summer pattern of
diurnally induced shower and thunderstorm activity forming along
seabreeze and outflow boundaries is expected. Heavy rainfall will
become a lesser threat, although hourly rainfall rates of 1 to 2
inches per hour can still be expected with the strongest storms
that form. However, the threat of strong wind gusts accompanying
these deeper convective cells will increase given the deeper pool
of dry mid-level air in place. The convection will dissipate in
the evening hours as temperatures cool from the upper 80s and
lower 90s into the 70s.

Going into Friday and Saturday, an inverted trough axis embedded
within developing deep layer easterly flow on the southern
periphery of a strong ridge over the Mid-Atlantic states will pass
through the northern Gulf and the forecast area. This trough axis
will bring higher PWATS of around 2 inches and increased upper
level lift to the area, and the end result will be higher PoP and
more numerous showers and thunderstorms each day. The convection
will remain diurnal in nature with peak activity occurring in the
afternoon hours as temperatures warm into the upper 80s and lower
90s, but the increased forcing aloft will support scattered
shower and thunderstorm activity along and south of the I-10
corridor both Thursday and Friday nights even as temperatures cool
into the 70s. Model sounding analysis indicates that some drier
air will continue to linger in the mid-levels over this period, so
both gusty winds and locally heavy rainfall will be a concern on
Friday and Saturday.

&&

.AVIATION...
(12Z TAFS)
Issued at 626 AM CDT Sun Jun 16 2024

The primary concern will be scattered thunderstorm activity
developing mainly after 18z and persisting through around 00z
as temperatures climb into the upper 80s and lower 90s.  Have
included a metion of VCTS in the 18z to 00z time period to
reflect the higher than average convective risk this afternoon.
Storm motion is decent, so any thunderstorm impacts will be
short-lived and have opted to not include any TEMPO wording for
today. At MSY, a more pronounced area of thunderstorms could
impact the terminal tomorrow morning with IFR visibilties due to
heavy rainfall around 15-16z, and I have included this in the
forecast.

&&

.AVIATION...
(06Z TAFS)
Issued at 313 AM CDT Sun Jun 16 2024

VFR conditions through the morning for all terminals. Beyond
this, convection will be on the increase generally from southeast
to northwest. Used PROB30s for the far west and northern
terminals. Used -SHRA and VCTS elsewhere given the low confidence
in timing and coverage. Under the heaviest storms, conditions may
drop to IFR, but for now given the lower confidence kept things
in the MVFR/VFR range. Subsequent forecasts may highlight changes
including the need for lower flight categories and perhaps short
fused TEMPOs.

&&

.MARINE...
Issued at 313 AM CDT Sun Jun 16 2024

Conditions will gradually worsen today into tonight over the open
Gulf waters as the pressure gradient between a high to the
northeast and a low to the southwest strengthens. By tomorrow
morning, small craft advisory conditions are expected to be in
place as easterly winds ramp up to 20 to 25 knots. These easterly
winds will remain in place through the end of the week and could
further strengthen to near gale levels on Tuesday and Wednesday
as the low to the southwest continues to deepen. Given the long
fetch of these 20 to 30 knot winds from the southeast Gulf into
the coastal waters a swell train of 3 to 4 feet is expected on
top of the wind waves of 5 to 8 feet, and this will push seas to
between 8 and 12 feet over the open Gulf waters on Tuesday and
Wednesday. Additionally, water will continue to pile up on east
and south facing shores over this period, and minor coastal
flooding of 1 to 2 feet above ground level is expected from
Tuesday through Thursday.

The low in the southwest Gulf should move into Mexico on Thursday
and Friday and the pressure gradient will begin to ease as the
low weakens. Winds will slowly ease from 20 to 25 knots on
Thursday to 15 to 20 knots by Friday. Given the extended duration
of small craft conditions, a small craft advisory is in effect for
the open Gulf waters and the Chandeleur and Breton Sounds from
Monday morning to Thursday morning. There is the potential that
winds could further increase into gale conditions, and a gale
watch may be issued closer to the event on Tuesday and Wednesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  91  72  86  72 /  40  40  80  70
BTR  91  74  86  75 /  50  40  90  60
ASD  89  75  86  75 /  50  40  80  60
MSY  88  78  85  79 /  50  40  90  60
GPT  87  77  86  78 /  50  40  70  60
PQL  88  75  87  76 /  50  30  70  60

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
LA...Small Craft Advisory from 7 AM Monday to 7 AM CDT Thursday for
     LAZ068.

GM...Small Craft Advisory from 7 AM Monday to 7 AM CDT Thursday for
     GMZ536-538-550-552-555-557-570-572-575-577.

MS...None.
GM...Small Craft Advisory from 7 AM Monday to 7 AM CDT Thursday for
     GMZ538-550-552-555-557-570-572-575-577.
-- End Changed Discussion --

&&

$$

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