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000
FXUS64 KLIX 190905
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
405 AM CDT Fri Apr 19 2024

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

.SHORT TERM...
(Today through Sunday Night)
Issued at 300 AM CDT Fri Apr 19 2024

Initially, light boundary layer flow of 5 knots will allow for
some boundary layer decoupling to occur over the next few hours,
and a few areas of dense fog may form in the Pearl River region of
the CWA before daybreak. The fog and low stratus will quickly
clear within a couple of hours of sunrise as temperatures warm and
the low level inversion lifts into a mid-level inversion layer. As
temperatures warm into the 80s, low level instability will
increase and some cumulus development is expected to take hold by
late morning. However, a strong mid to upper level ridge axis
will remain in control of the area today, and the subsidence
associated with this will keep a strong mid- level capping
inversion in place. Although temperatures will be warmer than
average and some low level instability will be in place, this
instability will be unable to overcome the capping inversion. The
result will be largely dry conditions continuing with only a few
sprinkles possible out of the deepest cumulus towers that form
this afternoon. Overall, PoP remains low at 10 percent or less for
today.

Tonight, the mid to upper level ridge axis will remain in control
of the area, but a weak frontal boundary is expected to slip
through Southwest Mississippi and into the Florida Parishes before
stalling somewhere near the I-12 corridor. The movement of the
front tonight will be nearly entirely driven by density
differentials between a cooler and more dense airmass to the north
and the warmer and less dense airmass to the south as there is no
strong synoptic level feature pushing the front southward tonight.
Despite the passage of this front, the mid-levels will remain very
dry to the continued subsidence aloft. This will keep a strong
capping inversion in place and no rainfall is expected tonight.
Additionally, boundary layer winds will remain light and humidity
values high, and this will support another round of low stratus
and fog development over the region late tonight into early
Saturday morning. Temperatures will also remain above average as
high dewpoints and the blanket of cloud cover prohibit much in the
way of cooling. Have opted to go with a blend of NBM 50th and NBM
75th percentile values for overnight lows. This keeps readings in
the upper 60s and lower 70s.

The front will move very little on Saturday, but rain chances will
increase by the late afternoon hours as the ridge axis shifts to
the east and a fast moving shortwave trough slides through the
region. A broad region of upper level ascent will combine with
some very weak isentropic forcing over the slightly cooler
airmass behind the front to induce some isolated to widely
scattered showers and possibly a weak low-topped thunderstorm in
the late afternoon hours Saturday. This will coincide with peak
heating when temperatures are expected to rise into the upper 70s
behind the front and the mid 80s ahead of the front.

Saturday night will see the front drift further south as rain
cooled air from the shower activity to the north increases the
density differential across the CWA. Once again, there will not be
a strong synoptic level forcing mechanism in place to drive the
front offshore, so the front will gradually sink south and should
stall somewhere near the Louisiana coast by Sunday morning.
Continued southwest flow in the mid and upper levels will continue
to produce isentropically forced rain shower activity through the
night, and a broad region of upper level positive vorticity
advection developing over the area by late Sunday night should
further reinforce the rainfall over the northern third of the CWA
where overall forcing will be greatest. Temperatures will see a
larger gradient as the combination of rain cooled air and weak
cold air advection on the back of northerly winds pushes lows into
the mid to upper 50s over Southwest Mississippi and the northern
Florida Parishes. Lows will be warmer from I-10 southward with
readings only cooling into the mid 60s.

Sunday into Sunday evening will be the most unsettled period of
weather as a much stronger shortwave trough axis sweeps through
the region. A weak mid-level low pressure system is expected to
form along the I-20 corridor Sunday morning and then quickly push
eastward through the day. This weak low will drive the front well
offshore by Sunday evening, and much colder temperatures are
expected across the entire region. Highs will only warm into the
low to mid 60s over most of the region, and this will result in a
broad area of isentropically induced rainfall impacting the region
through the day on Sunday. Model sounding analysis indicates that
mid-level lapse rates will be weak over the northern third of the
forecast area, and do not have thunderstorm activity in place for
this region. However, mid-level lapse rates are slightly more
favorable for some isolated elevated convective activity from the
I-10 corridor southward, and have this mentioned in the forecast.
As the trough axis and more favorable jet dynamics shift to the
east Sunday evening, increasing subsidence aloft will take hold
and lead to rapidly drying conditions from west to east through
the evening hours. By late Sunday night, any rainfall will be well
offshore and skies will being to slowly clear as a drier and cold
airmass moves in. Lows will be much colder with readings dropping
into the upper 40s and lower 50s.

&&

.LONG TERM...
(Monday through Thursday)
Issued at 300 AM CDT Fri Apr 19 2024

Deep layer northwest flow aloft on Monday will continue to usher
in a dry, stable, and cooler than average airmass into the region.
Skies will remain clear and temperatures will be below average in
the lower 70s. Lows Monday night will cool back into the upper 40s
and lower 50s as the combination of light winds and clear skies
supports strong radiational cooling.

Tuesday will see a weak and moisture starved shortwave trough
move through the region on the back of developing zonal flow.
Other than some scattered cirrus, there will be no evidence of
this system moving through the area. Temperatures will gradually
modify as the surface high shifts to the east and 925mb
temperatures climb. Highs will warm into the mid to upper 70s on
Tuesday and lows will be a good 10 degrees warmer Tuesday night
with readings in the upper 50s and lower 60s. Conditions currently
look favorable for another round of radiation fog development
late Tuesday night into early Wednesday morning.

Although a strengthening ridge axis over Texas will be the
primary influence on the forecast on Wednesday, a shortwave trough
riding over the ridge could push a frontal boundary close enough
to the northern CWA to spark off some isolated showers and
thunderstorms during the afternoon hours. Any convective activity
will be highly conditioned on the ability to break a fairly strong
mid-level capping inversion, and have only went with 20 percent
PoP due to this. Highs will continue to warm as onshore flow
strengthens and expect to see temperatures climb into the upper
70s and lower 80s. Lows Wednesday night will be little changed
with readings falling back into the upper 50s and lower 60s and
another round of patchy radiation fog will be possible.

By Thursday, deep layer subsidence will take hold as the ridge
axis over Texas shifts to the east and moves directly over the
forecast area. A strong capping inversion will keep rain chances
at bay even as a scattered cumulus field develops in the
afternoon hours. This cumulus field will be driven by ample low
level instability being fed by temperatures warming into the low
to mid 80s.

&&

.AVIATION...
(06Z TAFS)
Issued at 300 AM CDT Fri Apr 19 2024

A gradually strengthening inversion layer has allowed for ceilings
ranging from 800 to 1500 feet to develop at several of the
terminals in the past few hours. As the inversion further deepens,
ceilings of 300 to 500 feet and lower visibilities of 3 to 5
miles is expected to take hold at MCB, BTR, HDC, and ASD. The
inversion will quickly lift after 14z and return to MVFR and VFR
conditions is expected at all of the terminals.

&&

.MARINE...
Issued at 300 AM CDT Fri Apr 19 2024

Through Saturday night, winds will be largely from the southeast
at 5 to 10 knots and seas of 1 to 2 feet can be expected as high
pressure to the east dominates. However, a cold front will start
to move through the waters on Sunday, and this will shift winds to
the northwest at 10 to 15 knots by Sunday evening. Winds will
further intensify to between 15 and 20 knots Sunday night into
Monday as colder air advects over the warmer coastal waters. This
will briefly raise seas to 3 to 5 feet by Monday morning. A high
pressure system will pass directly over the waters Monday night
into Tuesday and winds will shift to the northeast and then
southeast over this period. Wind speeds will also drop to 10 to 15
knots as the heart of the cold pool shifts to the east. Southeast
winds will then persist on Wednesday and Tuesday at 10 to 15 knots
as high pressure slides into the eastern Gulf.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  86  68  78  55 /   0  10  50  70
BTR  87  69  83  61 /   0  10  30  60
ASD  85  70  83  62 /   0   0  20  40
MSY  84  71  83  64 /   0   0  20  50
GPT  81  69  80  62 /   0   0  20  30
PQL  81  68  81  61 /   0   0  20  20

&&

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

$$

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