Storm Warning 1, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
604 AM CST Sun Jan 7 2024

...New AVIATION...

.SHORT TERM...
(Today through Tonight)
Issued at 334 AM CST Sun Jan 7 2024

The short term period can generally be characterized as the
transition period. At the surface, a high pressure will quickly
move east over the region today. Aloft, the region remains in a
fairly active southwesterly flow...which has allowed some high
clouds to develop keeping our area from radiating effectively
this morning. By later tonight the high will be centered over the
southern Appalachians. At the same time, a lee-side trough and
developing low pressure will take shape across the high plains
leading to more pronounced onshore/return flow overnight tonight.
This return flow will help increase low level moisture transport
back into the region...however, overnight lows should remain
generally in the 40s across the region...at least early on before
a slight uptick in cloudiness and WAA help temperatures warm into
the upper 40s or lower 50s around daybreak on Monday. (Frye)

&&

.LONG TERM...
(Monday through Saturday)
Issued at 334 AM CST Sun Jan 7 2024

On Monday, the highly advertised system begins to impact our
local area. Pressure gradient will begin to increase as a surface
low develops over the high plains. The onshore flow will continue
to advect warmer and more moist air into the region. Aloft, a
strong trough will continue to migrate eastward toward our region.
With plenty of lift from aloft (H3 jet, difluent flow mid level
flow and ample low level convergence) showers and thunderstorms
should begin to breakout across the region by late morning or so.
Given the multiple hazards and impacts anticipated...we'll break
down each one by one.

Severe/convective potential:

Both global and mesoscale guidance
are indicating a warm front moving northward from the Gulf of
Mexico during the evening hours Monday. This could be the first
severe potential associated with the system. Initially, elevated
convection will be possible ahead of the warm front. Along the
immediate surface front, storms riding the front or storms just
prior to crossing the boundary will likely be surface based. The
shear profiles are very supportive during this time with
hodographs taking on a clear clockwise curve with surface winds
remaining backed as the surface low continues to deepen to our
north. Instability will not be extreme, however, SBCAPE 800-1200
J/kg during the "cool season" is enough to get the job done given
the strong upper level ascent. There are a few limiting factors
to consider such as how far north does the warm front moves and
whether or not cooler SSTs off the tidal lakes and MS Sound will
help develop a marine layer. Either/or (assuming all limitations
are countered) the second and third potential for severe will
come within the warm sector (where a low topped supercell or two
will be possible) along with a solid or broken squall line along
or just ahead of the front. Any storms that root into the boundary
layer will likely take on some rotation. Effective SRH over 400
m2s2 is quite high...which could be a bit much for weaker updrafts
to sustain. That said, the more robust updrafts will likely have
a tornado threat. Otherwise, with such strong dynamics, damaging
winds (convective winds) will be a concern, especially with the
final squall line (not to mention QLCS mesovort potential).

Hydro:

As widespread showers and storms erupt during the day on Monday.
Rainfall rates will gradually increase, especially as elevated
convection develops with cooling upper levels. Additionally, deep
moisture will feed in from the south or southwest with the
increasing H85 LLJ (generally at or above 65kt by the evening
time). Any SW to NE oriented line segment could have an excessive
rain threat. Also, despite the drought/antecedent conditions,
rainfall rates will be very efficient for this time of year. PWAT
values increase to around 1.7", which climatologically is at
record levels for the date. Because of this, WPC has introduced a
moderate risk for excessive rainfall. A Flood Watch for Flash
Flooding has been issued for the entire CWA to account for this
potential, though the best potential will be in the flood prone
areas such as urban and poor drainage areas. On average expect
2-4" of rainfall across the area with locally up to 6" not out of
the question (some of that falling in short order).

Non-convective Wind:

The wind advisory continues across the region from Monday
afternoon through Monday night. The pressure gradient between the
deepening low and the high across the central Appalachians will
allow winds to increase to 25-35mph with some gusts at or
exceeding 50mph at times. Considered high wind products, but the
recent runs continue to keep these wind speeds just below
criteria (sustained 40mph+ and/or gusts AOA 58mph). Winds of this
magnitude will become an issue for high profile vehicles as well
as any remaining holiday decorations left out. Some minor tree
damage could also take place along with sporadic power issues.

Coastal Flooding:

With the onshore flow ahead of the approaching cold front, an
increase in water levels can be expected along the eastward and
south facing shorelines. At this juncture, the typical hot spots
at Waveland and Shell Beach are forecast to be hitting warning
thresholds during high tide Monday into Tuesday. Will include all
of the MS Gulf Coast as well as the SE Louisiana Coast in a
Coastal Flood Watch. Will leave out the lake given the rather
short duration and quick transition of winds behind the front, but
further extension of at least an advisory cannot be ruled out.

The front moves through the region early Tuesday. This will allow
cold air to swiftly move in and winds will shift to a
northwesterly direction. With the strong CAA, expect midweek to be
below average. However, again, with these Pacific systems and
lack of snow-pack upstream, we will not cool off any cooler than
we've already seen this season.

By Wednesday and into Thursday, a surface high pressure will begin
to migrate into the region from the southwest. Aloft, a zonal
flow develops. The high pressure by Thursday moves off the
eastern coast of Florida allowing once again for another return
flow to develop and a warming trend. By late week and perhaps
into the early part of next weekend eyes refocus upstream over the
southern Rockies where an H5 trough begins to dig and another
surface low develops somewhere downstream of this feature. The
globals are in relatively poor agreement on this system so feel
for now we'll keep focus on the impacts of Monday/Tuesday and put
some of that burden onto the consensus output for Friday/weekend
system. (Frye)

&&

.AVIATION...
(12Z TAFS)
Issued at 559 AM CST Sun Jan 7 2024

Most of the area currently dealing with VFR condtions and the few
that aren't like BTR and HDC is a combination of MVFR cigs and/or
vsbys. There is even a slight chance that for a 30 min to hour
window that these two sites could drop into IFR but that would be
short lived as all terminals should be back in VFR status no later
than 1500. After that all terminals will likely remain in VFR
status for the remainder of this TAF package but later packages
this will not be the case. That said that doesn't mean there won't
be any impacts as winds will quickly start to ramp up in the BL
this evening and overnight and all terminals outside of NEW will
likely have LLWS issues beginning between 8 and 10z. NEW likely
won't because it will probably remain mixed allowing for stronger
sustained sfc winds and gusts already. /CAB/

&&

.MARINE...
Issued at 334 AM CST Sun Jan 7 2024

Marine conditions will start rather benign today, however, this
will be short lived as a surface low develops and deepens across
the southeast and northern Gulf Coast. As the low deepens,
pressure gradient will tighten during the day on Monday and into
Monday Night. Gale Conditions are expected to develop across all
waters, even the tidal lakes. Additionally, storm conditions are
also becoming increasingly likely, especially the offshore waters
beyond 20nm. A cold front will move through early Tuesday, which
will shift the winds to a more offshore direction. Although winds
do not appear to be as strong behind the front, Gale conditions
will likely linger well into early Tuesday. Eventually, high
pressure will begin to spread into the region late Tuesday and
into midweek, which should allow for winds and seas to relax back
to more favorable conditions. (Frye)

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  57  38  64  45 /   0   0 100 100
BTR  62  44  70  47 /   0  10 100 100
ASD  60  42  69  48 /   0   0 100 100
MSY  58  48  69  50 /   0  10 100 100
GPT  59  44  66  48 /   0   0 100 100
PQL  61  41  68  50 /   0   0  90 100

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Wind Advisory from noon Monday to 6 AM CST Tuesday for
     LAZ034>037-039-046>048-056>060-064>071-076>090.

     Coastal Flood Watch from Monday afternoon through Tuesday
     morning for LAZ066>070-076-078.

GM...Gale Watch from late tonight through Tuesday morning for GMZ530-
     532-534-536-538-550-552-555-557.

     Gale Watch from late tonight through Monday morning for GMZ570-
     572-575-577.

     Storm Watch from Monday afternoon through Tuesday morning for
     GMZ570-572-575-577.

MS...Wind Advisory from noon Monday to 6 AM CST Tuesday for
     MSZ068>071-077-083>088.

     Coastal Flood Watch from Monday afternoon through Tuesday
     morning for MSZ086>088.

GM...Gale Watch from late tonight through Tuesday morning for GMZ532-
     534-536-538-550-552-555-557.

     Gale Watch from late tonight through Monday morning for GMZ572-
     575-577.

     Storm Watch from Monday afternoon through Tuesday morning for
     GMZ572-575-577.

&&

SHORT TERM...RDF
LONG TERM....RDF
AVIATION...CAB
MARINE...RDF