Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA

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FXUS64 KLIX 232048
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
348 PM CDT Sat Mar 23 2024

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

.SHORT TERM...
(This evening through Tuesday)
Issued at 259 PM CDT Sat Mar 23 2024

Deep layer ridging will dominate the forecast area through
tomorrow night, and this will keep conditions very dry and very
stable. Winds will also relax tonight and remain subdued into
tomorrow night as a surface high passes directly over the area.
With clear skies, low dewpoints, and light winds in place a fair
degree of radiational cooling will occur, and overnight lows are
expected to fall into the 40s over inland areas and the 50s south
of the lake and along the Louisiana coast. Little temperatures
spread was noted between the models, and have opted to stick with
NBM deterministic values for overnight lows. However, the dry
airmass and strong solar insolation in place tomorrow will allow
temperatures to quickly rise into the lower 70s. Given that
temperatures have trended warmer than expected today, have opted
to use NBM 75th percentile values for daytime highs tomorrow. This
pushes highs back into the low to mid 70s tomorrow afternoon. By
tomorrow night, increasing onshore flow on the backside of the
ridge axis will allow Gulf moisture to feed back into the region.
Dewpoints will climb into the upper 50s and lower 60s, and
overnight lows will cool toward those temperatures. One would be
concerned about fog developing in these conditions as warmer air
moves over the cooler nearshore waters, but winds will be too
strong to support fog development. Instead, an extensive blanket
of low stratus will form over the area and remain in place
through Monday morning.

The main story for the short term period is the continued threat
of severe thunderstorms impacting the area from Monday evening
into Tuesday morning. A review of the NAM and GFS model soundings
indicates that conditions will be extremely favorable for severe
thunderstorms to impact portions of the forecast area, and that
the highest threat will be along and north of the I-10/12
corridor. All of this will be driven by a strong longwave trough
ejecting out of Texas from Monday into Tuesday, and taking on a
more negatively oriented tilt as an upper level jet streak rounds
the base of the trough. A highly difluent pattern aloft will form,
and a broad region of upper level lift will develop across the
Lower Mississippi Valley by Monday afternoon and evening. Further
down into the low to mid-levels, the formation of a 60+ knot low
level jet will take place Monday afternoon and this LLJ will be
the main driver of extremely high shear directional and speed
shear values over the region through Tuesday morning. Storm
relative helicity values in the lowest kilometer will exceed
350m2/s2 and effective bulk shear will approach 70 knots over the
northern third of the forecast area. This high shear will combine
with a moderate degree of MLCAPE nearing 1000 J/KG that forms as
mid-level lapse rates steepen to around 6.5C/km and temperatures
remain in the 70s. The combination of these factors and hodograph
analysis from the model sounding data continues to support the
idea that the severe storms will come in the form of a quasi-
linear convective system (QLCS) with several embedded bowing
segments and mesovorticies capable of producing tornadoes and
strong damaging wind gusts. This QLCS will from along a pre-
frontal trough axis that develops in close proximity to the low
level jet and most favorable upper level dynamics between the I-10
and I-20 corridors.

Conditions will quickly improve on Tuesday from west to east as a
surface front surging out of Texas catches up to the convective
line and pushes it to the east late Tuesday morning. By Tuesday
afternoon, the deepest convection will be well displaced from the
area across parts of Alabama, Georgia, and Florida. Strong
subsidence and dry air advection behind the front will lead to
rapidly clearing skies and expect to see a very warm and sunny day
across the area by Tuesday afternoon. There is a concern that
deep layer west to southwest flow and the subsident airmass could
lead to decent warming over the area. This is being picked up by
the ensemble members of the NBM that have a warmer bias on
Tuesday, and have opted to go with the NBM 75th percentile for
highs. This pushes highs in the lower 80s for most locations.

&&

.LONG TERM...
(Tuesday Night through Friday night)
Issued at 259 PM CDT Sat Mar 23 2024

Picking up the long range going into Tuesday night, main story
following the recent severe weather and frontal passage will be
ongoing CAA by drier/cooler continental air filtering in. Winds
while are not excessively strong, may remain elevated enough given
tighter SLP gradient helping to offset any contribution of
radiational cooling. Still wanted to emphasize a slightly cooler
bias given how long-range models are slow to handle cold, dense
surface air and related advection regimes. That brought in mid/upper
40`s north to 50`s south going into Wednesday morning with again, a
light ongoing breeze and clear skies.

Wednesday is looking overall beautiful as winds begin to taper some,
but still may be breezy given a strong mixed afternoon PBL and did
drop dewpoints to accommodate that. Still seeing winds slightly
elevated Wednesday night into Thursday morning as the surface high
is not quite close enough to reduce the SLP gradient, but is
noticeably reduced yielding in more of a radiational cooling
component. Given this, did apply a cooler nudge on lows into the
40`s widespread to low 50`s southshore.

It`ll be Thursday night into Friday morning when the surface high
settles in, priming the area for a strong radiational cooling
processes given calm surface winds and as the depth of the cooler
continental airmass settles in. Went full on the 25th percentile and
emphasized the drainage basins pulling in low 40`s. Not confident
enough to go lower than that at the moment leaning on the colder
side, and feel confident with this cooler target. Also, am taking
into account the higher sun angle helping to warm the surface
faster/hotter these days, meaning clear skies in a high pressure
dominated regime can really warm us up fast and did nudge highs a
tad warmer going into late-week, but overall such a nice and
pleasant rest of the week and even going beyond into next weekend
with no major impacts way out on the horizon. When it`s calm like
this, enjoy it! KLG

&&

.AVIATION...
(18Z TAFS)
Issued at 259 PM CDT Sat Mar 23 2024

A very dry and stable period of weather will be in place at all of
the terminals through the end of the forecast period. The result
will be prevailing VFR conditions for all terminals. The only
concern is continued gusty northerly winds of 20 to 25 knots at
times, but these will relax after 00z with the loss of daytime
heating. PG

&&

.MARINE...
Issued at 259 PM CDT Sat Mar 23 2024

Cooler and drier air moving over the waters will keep winds and
seas elevated through tonight over the eastern Gulf waters, but
conditions will quickly improve during the day tomorrow over all
of the waters as a surface high moves directly over the area.
Winds will fall to 10 knots or less and will also veer from the
north to the southeast through the day. This respite in stronger
winds will be short-lived as a potent area of low pressure starts
to approach from the west. Onshore flow will increase back into
advisory range by late Sunday night as the low intensifies and the
pressure gradient over the Gulf increases. These strong onshore
winds of 20 to 30 knots will persist through Monday night, and
there will be a concern for coastal flooding issues on south and
east facing shores. Fortunately, the tide cycle is in neap phase
right now, so the tidal ranges are not as high as normal. However,
some coastal flooding will still be likely. After the low moves
out of the area on Tuesday, conditions will rapidly improve with
winds falling to around 15 knots by Wednesday and Thursday as high
pressure builds over the waters and the pressure gradient eases.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  43  72  58  77 /   0   0   0  30
BTR  48  74  62  80 /   0   0   0  40
ASD  45  72  61  78 /   0   0   0  10
MSY  53  72  64  78 /   0   0   0  20
GPT  48  71  61  73 /   0   0   0  10
PQL  44  72  60  72 /   0   0   0  10

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Small Craft Advisory until 5 PM CDT this afternoon for GMZ530-
     532-534-536-538-550-552-570-572.

     Small Craft Advisory until 1 AM CDT Sunday for GMZ555-557-575-
     577.

MS...None.
GM...Small Craft Advisory until 5 PM CDT this afternoon for GMZ532-
     534-536-538-550-552-570-572.

     Small Craft Advisory until 1 AM CDT Sunday for GMZ557-575-577.

&&

$$

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


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