522
FXUS64 KLIX 232326
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
526 PM CST Sat Nov 23 2024

...New AVIATION...

.SHORT TERM...
(This evening through Monday night)
Issued at 230 PM CST Sat Nov 23 2024

A strong surface high pressure system will start to transition to
the east of the forecast area tonight into tomorrow. As this
occurs, southerly flow will begin to develop from 850mb down to
the surface. Moisture advection will take hold on the back of this
southerly flow regime, but the moisture will be limited to the
lowest 5000 feet or so of the atmosphere through Monday afternoon.
Farther aloft, a prevailing zonal flow regime will be the rule in
the mid and upper levels from 700mb up through 300mb. This pattern
will continue to usher in a drier and more stable airmass aloft,
and this will keep a fairly strong mid-level temperature inversion
in place through Monday afternoon. This will limit cloud
development to only a shallow layer of strato-cumulus development
starting tomorrow and continuing into Monday.

In addition to the moisture advection, warmer air will also
advect in from the south. Temperatures will be a good 5 degrees
warmer tonight with lows dipping into the mid upper 30s and lower
40s along and north of I-12 and the upper 40s and lower 50s south
of I-12. By tomorrow, temperatures will climb to 5 to 10 degrees
above average as southerly flow off the Gulf increases and
transports in a much warmer airmass. Overall, have opted to use
the NBM 75th percentile values for tonight and tomorrow to better
reflect the large diurnal range expected as warmer air surges into
the region tomorrow afternoon. This strong warm air advection
will push overnight lows into the 50s and lower 60s, or about 10
degrees above average, tomorrow night. Although humidity values
will be high, strong boundary layer winds of near 20 knots will
keep fog potential very low, and have opted to not include it in
the forecast tomorrow night. However, conditions do look favorable
for some low stratus to form in the morning. Monday will see
temperatures warm even further on the back of deepening southerly
flow with highs running a good 15 degrees above average or near 80
degrees. Given the small model spread tomorrow night into Monday,
have stuck with NBM deterministic values in this time period.

Monday night, a weakening cold front associated with a fast
moving northern stream shortwave trough axis will slip into the
forecast area. This front will transport some mid-level moisture
into the region, and this will help push PWATS up by about half an
inch to near 1.5 inches by late Monday night. This deeper pool of
moisture will interact with the front to induce some shower
activity mainly across northern and western portions of the CWA
starting as early as late Monday evening and continuing into very
early Tuesday morning. Fortunately, lapse rates will remain weak
as this front moves in and begins to dissipate, so no thunderstorm
activity is forecast in the area. Lows will remain mild as the
heart of the cold pool behind the front remains displaced to the
northeast of the region with readings running a good 10 to 15
degrees above average. Model spread is surprisingly small, so
confidence is high enough to stick with NBM deterministic output
Monday night.

&&

.LONG TERM...
(Tuesday through Friday night)
Issued at 230 PM CST Sat Nov 23 2024

The front will be fully dissipated by Tuesday afternoon, and zonal
flow regime in the mid and upper levels will take hold of the
area and remain in place through Wednesday afternoon. In the low
levels, a weak surface high will pass through the region Tuesday
afternoon into Tuesday night, but as the high pulls to the east on
Wednesday, low level winds will once again shift back to the
south. This will help usher in another round of low level moisture
advection beneath a mid-level inversion layer, and scattered
strato-cumulus development can be expected by Wednesday afternoon.
Temperatures will be near average Tuesday into Tuesday as weak
cold air advection in the wake of the weakening front slides in,
but a return to warmer than average temperatures is expected by
Wednesday on the backside of the departing surface high. Given
some differences in the timing of the southerly flow developing,
model spread is fairly large Tuesday night into Wednesday for
temperatures. Have opted to use the deterministic output of the
NBM until confidence on the timing of the warm advection into the
region improves over this time period. Fortunately, this all
important day before Thanksgiving looks great for those traveling
into or out of the region with no significant weather concerns
expected.

Thanksgiving day and night will see another round of unsettled
weather move into the region as a strong positively tilted
longwave trough axis and associated surface front sweep through
the region. Moisture and warm air advection back into the area
will continue Wednesday night as deep layer southwest flow takes
hold. Temperatures will only dip into the 60s, or near the average
highs for this time year, and PWATS will surge back to around 1.5
inches. This is more than enough moisture when combined with
increasing omega in advance of the approaching trough to produce
widespread cloud development and scattered shower activity. In
fact, there may be just enough mid-level cooling to support SBCAPE
near 1000 J/KG across the northern third of the CWA on Thursday,
and have included a slight risk of thunderstorms for this portion
of the CWA. Fortunately, wind shear will remain limited, so no
severe thunderstorm activity is currently expected in the forecast
area. Highs on Thursday will easily climb into the upper 70s on
the back of the deep layer southwest flow which further supports
the barely sufficient CAPE values for thunderstorm activity mainly
in the afternoon hours.

The front is expected to push through in the evening hours, and
winds will quickly shift to the north. These northerly winds will
allow a much colder airmass to move in and overnight lows will
drop back to near average readings in the 40s and lower 50s by
late Thursday night. Model soundings suggest that some lingering
low level moisture will remain trapped beneath an inversion that
forms as cold air near the surface moves and westerly flow aloft
remains in place. A few light rain showers and overcast skies will
be possible through daybreak on Friday, and this reflected by 20
percent PoP values lingering into late Thursday night. The cloud
layer will clear quickly Friday morning as the inversion weakens
due to daytime heating and drier air aloft mixes down to the
surface. Clear skies, low humidity, and breezy north winds will
then be the rule through Friday night with temperatures running an
average of 5 degrees below normal.

&&

.AVIATION...
(00Z TAFS)
Issued at 524 PM CST Sat Nov 23 2024

VFR conditions will prevail through the period under the influence
of dry high pressure. As the high shifts eastward Sunday, winds
will become southerly but should remain below 10 kts.

&&

.MARINE...
Issued at 230 PM CST Sat Nov 23 2024

Overall, no significant impacts to maritime operations are
expected across the coastal waters through Wednesday afternoon.
Winds will be variable during this period as a series of weak high
pressure systems and a frontal boundary move through the waters,
but winds are not expected to rise much higher than 10 knots over
this entire period. The end result will be relatively calm seas of
3 feet or less. Wednesday night into Thursday will see the
pressure gradient over the Gulf increase in advance of a stronger
approaching front, and this will push conditions into at least
small craft exercise caution range of 15 to 20 knots. Seas will
respond, and should be in the 4 to 6 feet range by Thursday
afternoon over the outer waters. The front will sweep through
Thursday evening, and winds will quickly shift to the northwest
late Thursday night and also increase in speed to advisory levels
over 20 knots. These rougher conditions are expected to persist
into Friday night as colder air advects into the region.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  39  75  55  78 /   0   0   0   0
BTR  43  77  60  79 /   0   0   0   0
ASD  41  76  57  78 /   0   0   0   0
MSY  52  77  61  78 /   0   0   0   0
GPT  45  74  60  76 /   0   0   0   0
PQL  40  75  57  77 /   0   0   0   0

&&

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

$$

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