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

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FXUS64 KLIX 171735
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
1235 PM CDT Sun Mar 17 2024

...New AVIATION...

.UPDATE...
Issued at 633 AM CDT Sun Mar 17 2024

Temperatures and dew points have been increasing south of
Interstate 10 since the issuance of the forecast package several
hours ago. Galliano was 63/62 at 3 AM CDT, they are now 70/68.
Surface pressure fields would also argue that there is a warm
front somewhere pretty close to Lake Pontchartrain, which would
help explain the fog at Gulfport and Slidell. This fog should be
pretty short-lived as the warm front continues to shift northward.
We`ll get a better look at the 12z sounding in the next 30 minutes
or so to more fully assess the severe weather and heavy rainfall
threat in real time.

&&

.SHORT TERM...
(Today through Monday)
Issued at 350 AM CDT Sun Mar 17 2024

Northern stream upper low to the north of the Great Lakes, with a
strong shortwave dropping through the Dakotas and Minnesota this
morning. The western upper low remains near Las Vegas. In advance
of the western low, a shortwave, and an associated convective
complex were moving through central and southern Texas. The old
frontal boundary or outflow boundary appears to be along the lower
Louisiana coastline. Temperatures across the local area were
generally in the 60s early this morning. Radar in the last hour
has started to show a few rain showers in the Lake Charles area,
but most thunderstorms were further south of Lake Charles over the
Gulf of Mexico or back in eastern Texas.

Most of the main concerns in the short term will be in the first
12 hours of the forecast (today), regarding the potential for
severe weather or heavy rainfall. Question isn`t so much IF there
is going to be an area of heavy rainfall as it is where to place
it. Precipitable water values that were close to 1.4 inches on the
00z LIX sounding are forecast to be much closer to 1.75 by mid
morning, near the climatologic max for mid-March.

Watching satellite loops over the last few hours has muddied
things a little, as there have been multiple MCVs noted that have
not had a particularly long life cycle. The furthest south one 2
hours ago has gotten pulled northward and absorbed into another
one over central Texas. A small area of cooling cloud tops is
noted well in advance of the main cluster to the south of Lake
Charles. The question at this point is which feature to key on to
suggest a future track of the complexes, as the surface, 925 mb
and 850 mb boundaries are progressively further north across the
local area. Any convection allowing model solutions that keep the
entire system offshore are quickly falling out of favor. Still
appears that the greatest threat area for heavy rainfall is front
Interstate 10 southward, but it won`t take much of a northward
shift to put Baton Rouge, New Orleans and the Mississippi coastal
cities in the crosshairs. One saving grace is that it appears
convection may be limited to one distinct round of convection
ending by mid- afternoon, where quite a few of the CAMs yesterday
were depicting 2, about 6 hours apart. Hopefully, that keeps
things fairly progressive, which would hold down precipitation
totals somewhat. Will continue to carry mentions of 1-3 inch
totals in our DSS and social media missives this morning. If
there`s any slice of good news, it`s that the severe threat
continues to appear to be rather limited, but not zero. While
we`ve opted not to go with a Flash Flood Watch at this point, we
won`t rule out a forecast update to issue a short one this
morning.

Could still be a few lingering showers or a rumble of thunder very
early this evening, but significantly drier air will arrive prior
to sunrise Monday. That will set the stage for a breezy day with
quite a bit of sunshine, especially in the afternoon, with
noticeably lower humidity levels.

Will keep the NBM numbers for today with concerns about clouds and
precipitation. For much of the area, little spread in guidance, so
not much of a target for adjustments. On Monday, trended toward
the warmer temperature guidance where there were differences,
except over southwest Mississippi closer to the cold air. Did make
a downward adjustment to dew points on Monday, closer to the NBM
25th percentile. We`ll need to keep a bit of an eye on things in
this regard, considering the breezy conditions anticipated
tomorrow. If dew points come in lower than what we`ve currently
got in our grids, that could bring humidities down into the range
where fire weather concerns increase.

&&

.LONG TERM...
(Monday night through Saturday)
Issued at 350 AM CDT Sun Mar 17 2024

Two issues to focus on in the long term portion of the forecast.
The first is the potential for a short, light freeze across the
northern half of the area Tuesday morning. The second would be the
potential for another round of showers and thunderstorms around
Thursday.

Monday night/Tuesday morning, we`ll have clear skies and very dry
air in place with dew points ranging from the mid 20s to lower 30s
by sunrise. The main limiting factor is likely to be whether the
winds drop off to close to calm. At this point, that`s somewhat in
question, as even a 3-5 mph wind could stop temperatures from
cratering as low as they could. At present, the only area that we
have forecast to reach freezing Tuesday morning would be southwest
Mississippi. NBM probabilities of a freeze for that area range
from 30 to 60 percent. That area is just past their average last
freeze, but they`ve been warm for the last 3 weeks, so if that
forecast maintains, later forecasts may need to issue Freeze
Watches and/or Warnings for northern portions of the area.
Portions of the area from the Interstate 10/12 corridor southward
generally have a 20 percent or less chance of reaching 32.

The southwest upper low finally starts to move eastward on
Tuesday in a weakening state. Surface high pressure will shift
eastward across the area on Tuesday and be off the Florida East
Coast by Thursday evening. The GFS and ECMWF 00z operational runs
differ as to the strength of the shortwave, and whether there will
be any significant surface pressure reflection associated with
the shortwave. The GFS solution would mean another round of rain
Thursday and Thursday night, while the ECMWF solution is
essentially dry. The NBM is tracking more with the GFS at this
time, but don`t have a reason to shy away from that solution
quite yet. Next weekend does look dry at this time.

&&

.AVIATION...
(18Z TAFS)
Issued at 1225 PM CDT Sun Mar 17 2024

Most terminals at IFR conditions with low CIGs, exception is KHUM
at MVFR. SHRA and TSRA remain in the area, but expected to begin
clearing west to east through the afternoon and early evening.
While visibilities are expected to improve late this afternoon,
ceilings will be slower to improve, with MVFR ceilings during the
overnight hours. Improvement to VFR unlikely until the daytime
hours on Monday. Gusty north winds gusting to 30 knots or more
will be possible at KNEW and KMSY later tonight and Monday.

&&

.MARINE...
Issued at 350 AM CDT Sun Mar 17 2024

Main concerns to mariners will be the potential for thunderstorms
today, and gusty northerly winds behind the frontal system on
Monday.

There will be the potential for a line of thunderstorms moving
through the waters later this morning through about mid afternoon.
This would have the potential to produce very windy conditions
with and immediately behind the line of storms. Some of the
convection allowing models are depicting signs of a wake low
associated with the convective line. If this does develop, a short
fused gale warning may eventually be necessary.

Regardless of the outcome of todays storms, colder and drier air
will arrive Monday across the waters on northerly winds. Small
Craft Advisories have been issued for Monday and Monday night for
all waters. There could be a few gusts to near gale force Monday
evening. Conditions should then improve for several days, until
perhaps Thursday afternoon or Thursday night, depending on whether
low pressure develops over the northern Gulf on Thursday.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  46  61  32  62 /  10   0   0   0
BTR  52  66  38  64 /  20   0   0   0
ASD  52  67  35  63 /  30   0   0   0
MSY  56  66  44  61 /  40   0   0   0
GPT  52  66  38  61 /  30   0   0   0
PQL  52  69  34  63 /  40   0   0   0

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Small Craft Advisory from 7 AM Monday to 7 AM CDT Tuesday for
     GMZ530-532-534-536-538-550-552-555-557-570-572-575-577.

MS...None.
GM...Small Craft Advisory from 7 AM Monday to 7 AM CDT Tuesday for
     GMZ532-534-536-538-550-552-555-557-570-572-575-577.

&&

$$

SHORT TERM...RW
LONG TERM....RW
AVIATION...DS
MARINE...RW


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