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

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FXUS64 KLIX 212350
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
650 PM CDT Thu Mar 21 2024

...New AVIATION...

.SHORT TERM...
(This evening through Friday night)
Issued at 253 PM CDT Thu Mar 21 2024

A vigorous shortwave trough currently moving through west Texas
will continue to advance toward the Lower Mississippi Valley
tonight and then pass directly over the region during the day
tomorrow. Initially, the combination of upper level difluence and
favorable jet dynamics will continue to support the development of
a mesoscale convective system over the open Gulf waters.
Fortunately, the primary convection with this system will remain
displaced well offshore, and only expect to see a broad shield of
light to moderate rainfall impact the forecast area through the
evening hours. Rainfall will be most prevalent for areas south of
I-10, and this is reflected in the PoP forecast for this evening
with likely or higher PoP to the south and chance PoP to the
north. The rainfall will help cool temperatures toward the
dewpoint with readings falling into the 50s.

Late this evening, a brief respite in the rainfall is expected as
the greatest upper level forcing and most favorable jet dynamics
shifts farther to the east. However, this short-lived break will
come to an end late tonight into tomorrow morning as the cold core
of the upper level passes directly over the area. Model sounding
analysis indicates that 500mb temperatures will drop to around
16 to 17 degrees below zero centigrade and wet bulb zero heights
will decrease to around 8000 feet by the afternoon hours. Ongoing
scattered shower activity in the morning over the northwest
portion of the CWA will transition to more robust and deeper
convection in the late morning and afternoon hours as temperatures
climb into the low to mid 70s and overall instability increases
due to the cold temperatures aloft. As a result, there is a risk
of seeing a few strong to severe storms form, especially in the
afternoon when lapse rates are steepest. The primary threat from
any strong to severe storms will be large hail, but drier air in
the mid-levels will also support the risk of occasional damaging
wind gusts. By tomorrow night, the core of the cold pool aloft
will shift to the east. Combining that with the loss of daytime
heating will effectively put an end to the convective threat, and
have dry conditions in place by midnight across the entire
forecast area. Since there is little in the way of surface based
cold air advection expected, lows will once again dip into the 50s
tomorrow night.

&&

.LONG TERM...
(Saturday through Wednesday night)
Issued at 253 PM CDT Thu Mar 21 2024

Increasing negative vorticity advection associated with a
strengthening longwave trough developing over the Plains states
will result in clear skies, lower humidity, and very pleasant
conditions for the weekend. Highs will be near average in the low
to mid 70s each day. Drier air in place will support lows falling
into the 40s and lower 50s Saturday night, but winds shifting to a
more onshore component by Sunday night will start to usher in
higher dewpoints and an overall warmer low level airmass. These
higher dewpoints will result in lows only dipping into the upper
50s and lower 60s Sunday night. At this time, winds are expected
to be too strong to support fog development, but conditions will
be favorable for overcast skies to form as the warmer air moves
over the cooler nearshore waters.

The next rain and severe weather threat will occur late Monday
afternoon through early Tuesday morning as a strong longwave
trough approaches from the west. A more difluent flow pattern
aloft will induce a broad area upper level lift across the region.
At the same time, a moderately unstable airmass is expected to be
in place as moisture deepens and temperatures warm into the mid to
upper 70s Monday afternoon. Although MLCAPE will remain somewhat
subdued at between 500 and 1000 J/KG Monday into Monday night,
the development of a 50+ knot low level jet over the area will
combine with the favorable upper level conditions to induce
enough deep layer forcing to support the formation of a convective
line along a developing frontal boundary in western Louisiana.
This convective line will interact with both very strong
directional and speed shear, and expect to see the line take on a
quasi-linear orientation with embedded bowing segments and a few
tornadoes possible as it moves across southern Mississippi and
portions of Southeast Louisiana. The highest threat appears to be
late Monday night into early Tuesday morning when low level jet
dynamics are maximized.

Conditions will quickly improve by Tuesday afternoon as a surge of
much drier mid-level air feeds into the region. Skies will quickly
clear and winds will shift to the northwest and north. The mid-
level drier air will persist over the area on Wednesday even as
the heart of the upper level trough moves through the
area, and this will keep conditions dry and stable in the low
levels.  Although some weak cold air advection will take place,
temperatures are still expected to be near average on both Tuesday
and Wednesday.

&&

.AVIATION...
(00Z TAFS)
Issued at 642 PM CDT Thu Mar 21 2024

Periods of light to moderate rain will continue to move east and
out of the area through the remainder of the evening. Expect IFR
CIGS to begin to move overhead terminals over the next few hours
as evident by obs from southwest and central LA which already have
MVFR to IFR CIGs. IFR conditions should persist through morning
hours with CIGs expected between 300-800ft. Scattered showers and
a few thunderstorms capable of producing hail will accompany the
passage of this upper level low and associated cold pool in the
timeframe of 12-18z Friday. May need inclusion of TS in TAF lines
in the successive forecast packages for this period if confidence
increases of impacts to terminals.

&&

.MARINE...
Issued at 253 PM CDT Thu Mar 21 2024

A low pressure system passing through the area tonight will induce
a brief period of small craft advisory conditions over nearly all
of the open Gulf waters. Conditions will briefly fall below
advisory levels as winds drop to around 15 knots, but another
surge of drier and cooler air into the region over the weekend
will likely lead to winds rising back above 20 knots. Small craft
advisories are expected to be needed from tomorrow night through
Saturday night. The pressure gradient over the waters will ease a
bit on Sunday, but the approach of another low pressure Sunday
night into Monday will produce an extended period of stronger
winds and higher seas through Tuesday. There is some concern that
the extended duration of strong and long-fetch onshore flow
Monday into Monday night could lead to some coastal flooding
issues.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  52  71  52  70 /  70  90  30   0
BTR  56  74  55  73 /  80  70  10   0
ASD  56  74  55  73 /  60  80  10   0
MSY  58  75  57  72 /  70  70  10   0
GPT  58  72  56  73 /  50  80  20   0
PQL  56  71  55  73 /  50  90  20   0

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Small Craft Advisory until 7 AM CDT Friday for GMZ550-552-555-
     570-572-575-577.

MS...None.
GM...Small Craft Advisory until 7 AM CDT Friday for GMZ552-555-570-
     572-575-577.

&&

$$

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


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