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

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000
FXUS64 KLIX 130429
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
1129 PM CDT Wed May 12 2021

.AVIATION (06z TAF package)...

About half of the terminals VFR this evening, but the remainder
are reporting MVFR ceilings. Seeing a slow dissipation of the MVFR
layer from the north as drier air works in, but as wind speeds
drop off again toward sunrise, could see the lower deck redevelop.
At this time, expect most to remain in the MVFR range, but at
least some threat of IFR ceilings. Winds not likely to decouple
enough for fog. MVFR ceilings should improve to VFR by mid-day,
and expect no ceiling restrictions for the back half of the
forecast period. 35

&&

.PREV DISCUSSION... /issued 632 PM CDT Wed May 12 2021/

EVENING UPDATE...

Allowed Flash Flood Watch to expire on schedule at 6 pm, and
issued zone update to remove the headline. Still seeing some
isolated to scattered showers moving southeastward on the nose of
the drier air aloft south of Interstate 12, but haven`t seen any
indications of lightning over the last hour or two. May see a
diminishing trend after sunset. Likely to see at least one more
update during the evening shift to handle precipitation trends.

PREV DISCUSSION... /issued 346 PM CDT Wed May 12 2021/

SHORT TERM (This evening through Friday night )...

Starting off with recent radar/satellite trends early this
afternoon, most of SE LA and southern MS remains in a generally
persistent northerly flow following an early morning mesoscale
complex that caused severe weather across a few areas. Noticing
the residual anvil canopy steadily thin out and diminish with
time, with low-level Cu streets developing in a destabilizing
environment. CAM`s have been a real struggle, not only today but
for several days. Large-scale ascent lacks in this type of
environment, with no real supportive low-level convergence from
any boundaries at the surface (the boundary that many CAM`s today
re-initiated convection on was forecast to stall up across I-10/12
or south across SE LA, when in reality this boundary draped well
south into coastal offshore marine zones). This convection
offshore will continue to dissipate, but still supports some
isolated to scattered convection to re-develop mostly east of I-55
this evening. Due to this slight possibility of development,
combined with slow storm motions and wet antecedent conditions,
have decided to extend the Flash Flood Watch until 6PM CDT to
account for any one storm possibly causing additional flooding,
depending on where this activity sets up. Riding on the lower end
of PoP`s through early tonight though, as confidence is low on
exact location and coverage potential. If trends continue to
remain dry, will cancel early. Not anticipating any severe
weather, due to a prominent moist- adiabatic moisture profile
limiting lapse rates, regardless of modest instability building
early this afternoon, but cant rule out an isolated strong storm
or two.

Going into tonight, drier air will continue to filter in from the
north, with any convection that does develop coming to an end.
Going through short-range model soundings, noticing a lingering
supply of low-level moisture, roughly between 700mb to just above
the surface. This may keep partly to mostly cloudy skies around
all night, with Td`s continuing to fall through daybreak Thursday
thanks to shallow CAA at work. Thursday will be a very nice day
and will feel a bit drier, with surface dewpoints around 10
degrees cooler than experienced today. However, clouds will be
stubborn to break up with lingering moisture in the lowest
tropospheric levels. Over time, clouds will break up, especially
through Thursday night as surface high pressure builds in across
the mid MS valley region - owing to drying/compressional warming
in the vertical and clearing aloft but... the sun will return.
Can`t wait.

By Friday, high pressure remains in control of the area with
light easterly winds. Still some low-level moisture lingering
which may support some Cu development, but generally a nice day
with highs maintaining on the higher end of NBM ensemble spreads
(few degrees above deterministic) with dry and pleasant weather
extending into the overnight hours.

LONG TERM (Saturday through Tuesday)...

Going into this weekend, high pressure pulls east allowing for a
steady return flow of deeper Gulf moisture. Highs a few degrees
warmer but still a few degrees below normal. Noticing a few recent
runs of the GFS hinting at a weak shortwave riding a quasi-zonal
flow aloft, which will re-introduce increasing clouds and a slight
increase of rain chances. Confidence remains low on exact
mesoscale details, if this will be more of a disorganized cluster
or organized complex, but will wait to resolve details as we get
closer. Beyond this time frame going into early next week, the
large-scale pattern quickly evolves with a series of cut off
upper-lows/shortwaves underneath amplifying ridging across the
central US. This will cause a rather tricky forecast in this time
frame, as several waves of severe weather across the central and
southern Plains. Unsure on how far east each potential convective
complex will push towards our area, but again since this will be
resolved by mesoscale models better, this will continue to be
advertised as a low-confidence forecast through atleast the middle
of next week. KLG

MARINE...

Ongoing northerly winds/offshore flow from an earlier convective
complex will persist early tonight, with some showers and storms
across offshore SE LA. Expect a drying trend going into late-week
and into the weekend, with relatively weak waves/seas. A steady
transition into an onshore flow will build by late weekend into
early next week, as high pressure pushes east across the east
coast. Scattered shower/storm chances will return by late weekend
and into early to middle next week, but will maintain a low
confidence forecast in regards to details for each potential
cluster of showers and storms. KLG

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  58  77  53  79 /  10  10   0   0
BTR  61  78  56  81 /  10   0   0   0
ASD  61  79  55  81 /  20   0   0   0
MSY  67  79  64  80 /  30  20   0   0
GPT  61  78  57  80 /  20   0   0   0
PQL  59  78  55  80 /  20   0   0   0

&&

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

$$


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