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FXUS64 KLIX 100158
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
858 PM CDT Thu May 9 2024

...New UPDATE...

.UPDATE...
Issued at 821 PM CDT Thu May 9 2024

In the very near term (0-3 hours), forecast is in good shape with
no forecast updates imminent. Main concern continues to be
potential for severe weather across the northern third to northern
half of the area later tonight. SPC recently issued Severe
Thunderstorm Watch 225 through 3 AM CDT for counties/parishes just
north and northwest of our CWA. Watches for any portions of our
area of responsibility are likely a few hours away from being
issued.

The frontal boundary at 8 PM CDT was generally in the vicinity of
Interstate 20. The 00z LIX sounding continues to show a very
unstable, but capped, airmass with a warm nose around 790 mb. CAPE
values in excess of 4700 J/kg were in place, with a lifted index
of -11, with steep mid level lapse rates above the cap. The LCH
sounding showed a much weaker cap, and it was non-existent in the
JAN sounding. The area of highest concern continues to be our
southwest Mississippi counties, with some uncertainty as to how
far southward any convective outflow can modify the airmass
sufficiently to erode the cap. At this point, the southward extent
of the main threat appears to be the Interstate 10/12 corridor.

&&

.SHORT TERM...
(This evening through Saturday night)
Issued at 245 PM CDT Thu May 9 2024

A vigorous vorticity max and associated 100+ knot upper level jet
streak is currently moving through Texas this afternoon and will
pass through the Lower Mississippi Valley and Gulf South tonight
into tomorrow morning. Strong deep layer ascent has been noted
with this system over Texas today, and this same ascent will move
through the forecast area tonight. This deep layer forcing will
tap into a very moist and highly unstable airmass, and this will
allow any convection that moves in from Texas to maintain itself
through the overnight hours. In terms of moisture and instability,
PWATS will be near 2 inches tonight and very steep mid-level lapse
rates of around 8.0 C/KM will support MLCAPE values on the order
of 3000 J/KG. Thus, there will be no form of capping inversion to
inhibit updraft growth and sustainment over the area.
Additionally, the steep lapse rates in place will also allow for
easier downward transport of stronger winds aloft and this
reflected by very high downdraft CAPE values of 1000 J/KG. The
passage of the jet streak aloft will increase 0-6km shear values
to around 60 knots and these stronger winds will easily descend
toward the surface in the form of a rear inflow jet behind the
developing convective line over east Texas later this evening. The
latest CAMS have trended further to the south and there is more
confidence that a strong bow echo will impact portions of
Southwest Mississippi and portions of the Florida Parishes late
this evening into the early morning hours tomorrow. Winds in
excess of 60 knots are absolutely possible with this bowing
segment. Large hail may also be a concern given the high MLCAPE
values and steep mid-level lapse rates. Any wind driven hail would
lead to additional damage to buildings and vehicles. The most
likely timing for this bow echo to impact the area will be between
11 PM and 5 AM based on the latest guidance.

The cold pool in the wake of the convection will allow a front
currently draped over north Louisiana to surge southward late
tonight into tomorrow morning, and fully expect to see the front
clearing the CWA by late tomorrow morning. Strong dry air and
negative vorticity advection will follow the front and the
departing upper level vort max tomorrow into tomorrow night, and
this will lead to rapidly clearing skies tomorrow afternoon. One
caveat is that colder air is not expected to initially move into
the area, and the combination of increasing solar insolation, weak
downslope heating on the back of northerly winds, and dry air will
allow temperatures to climb into the upper 80s and even lower 90s.
The colder air will finally move in by tomorrow night, and
temperatures will rapidly fall into the upper 50s and 60s by
Saturday morning. Temperatures will be near average for Saturday
with highs warming into the low to mid 80s and lows dipping back
into the upper 50s and 60s Saturday night.

&&

.LONG TERM...
(Sunday through Wednesday night)
Issued at 245 PM CDT Thu May 9 2024

Long term forecast looks active. Overall the medium range global
models have the same general idea showing a very progressive
pattern with multiple impulses and s/w moving through. Obviously
there are timing issues between the models but they all show what
could be 3 to 4 rounds or more of rain. Latest NBM is in full
agreement. The biggest question is how much rain do we eventually
get and temperatures. The amount of rain is extremely difficult to
try and predict however the temperatures appear to be a little
too warm if we are expecting as much rain and cloud cover. Made
some small deviations a degree or two lower for highs but overall
stuck with the latest NBM until we can get a better idea of
timing.

We begin with the end of the weekend and likely one last pleasant
day however, there is a chance that rain tries to move in from the
west as early as Sunday evening. The ridge aloft should start to
move east of the area late Sunday as a deep s/w moves across the
Continental Divide and into the Plains. That along with the southern
stream will start to increase the mid lvl flow and we could see the
first impulse move across the coast and Lower MS Valley Sunday
evening and night.

As we move into the work week moisture will increase quite
significantly with PWs easily over 1.75" and possibly over 2" before
sunrise Monday. PWs stay that high until midday/afternoon Tuesday
when drier air from the north could infiltrate the region
temporarily, PWs may fall below 1.25". However, this will be short
lived as moisture looks to quickly rebound overnight Wednesday with
PWs approaching 2" once again early Thursday morning.

With moisture this abundant it will not take much to get convection
to fire and with any disturbance/jet streak we could easily see
numerous to widespread convection. How much rain is basically impossible
to discern and multiple things go into this:

- Instability: we will be unstable how unstable depends on timing
  and whether we get much sun.
- Jet strength and placement: All levels, LL jet increasing or
  decreasing the LL convergence, Mid lvl adding that extra forcing,
  Upper lvl location enhancing the or hindering the diffluence/divergence
  aloft
- Timing/strength/location of impulse and s/w`s: this sort of goes into
  the previous two but this also will determine where convection
  initiates and how it evolves. Also determine where and how strong any
  sfc features are which will also dictate precip placement.

Depending on how these ingredients come together we could have multiple
rounds of storms some of which could be quite efficient. At this time
if everything runs similar to what is being advertised it is not out of
the question to see widespread 4 to 7" of rain with locally higher
amounts likely. Take that with a grain a salt though because again just
one or two things slightly different will easily impact location,
timing, and amounts. One example is if we get an MCS to develop over
the coast and just into the Gulf as this would drastically lower the
rain potential inland for that round. The rain is wanted but depending
on things set up it could be a tad more than we really want. /CAB/

&&

.AVIATION...
(00Z TAFS)
Issued at 622 PM CDT Thu May 9 2024

Frontal boundary remains well to the north of the local area, near
Interstate 20, early this evening. Moist southerly flow continues
to produce SCT-BKN clouds in the FL010 to FL030 layer. As has
happened the last couple nights, most or all terminals will
develop MVFR ceilings by around 03z, continuing for most of the
night. Main forecast concern overnight will be the convective
threat, and how far south threat will exist. The highest threat
will be at KMCB, with severe storms possible, but at least a
reasonable chance as far south as KBTR/KHDC/KASD/KGPT. Amendments
will likely be necessary as we better refine timing of convection
and potential for direct impacts. Direct impacts will include IFR
or lower conditions, especially visibilities. Frontal boundary
should move south of all terminals by midday Friday with VFR
conditions expected beyond that point.

&&

.MARINE...
Issued at 245 PM CDT Thu May 9 2024

Southerly flow near 15 knots will persist over the waters tonight
in advance of an approaching cold front. The front will move
through the water tomorrow morning, and a surge of colder air into
the area tomorrow night will lead to a brief period of stronger
offshore flow to near 20 knots. Seas will also remain somewhat
elevated in the 3 to 5 feet range over this period. High pressure
passing through the area Saturday into Saturday night will lead to
lighter winds of 10 knots or less, calmer seas, and more variable
wind directions. By Sunday, the development of a broad area of low
pressure over the Plains and a high to the east will increase
southeast gradient winds back into the 15 to 20 knot range. These
stronger onshore winds and resultant higher seas will persist
through Tuesday as the low tracks to the north of the area and the
high remains in place. PG

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  67  85  59  81 /  60  20   0   0
BTR  73  88  64  84 /  30  10   0   0
ASD  73  90  63  85 /  30  30   0   0
MSY  76  88  69  83 /  20  20  10   0
GPT  73  90  64  85 /  40  40   0   0
PQL  72  90  62  86 /  40  40   0   0

&&

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

$$

SHORT TERM...PG
LONG TERM....CAB
AVIATION/UPDATE...RW
MARINE...PG