163
FXUS64 KLIX 182354
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
654 PM CDT Thu Jul 18 2024

...New UPDATE, AVIATION...

.UPDATE...
Issued at 645 PM CDT Thu Jul 18 2024

Will likely do a brief update prior to 8 PM CDT to trim evening
PoPs back a bit. Convection allowing models indicate some
potential for convective redevelopment toward sunrise, so unlikely
to mess with that time period very much, if at all. As usual, will
massage hourly temperatures and dewpoints to reflect current
trends.

&&

.SHORT TERM...
(This evening through Friday night)
Issued at 255 PM CDT Thu Jul 18 2024

The storms we`re seeing today are indicative of the general weather
pattern that`ll be present through the entire forecast period. The
upper level low to our southwest is increasing divergence and lift
area wide such that convective coverage has become more widespread.
An old MCV from an MCS over north Texas last night is also providing
mid-level PVA that is boosting upward motions across Louisiana and
Mississippi as it tracks southeast. The upscale growth of these
cells into a QLCS has bolstered a cold pool that is keeping rainfall
across the western CWA as stratiform, but we cannot rule out
additional initiation later today. Thankfully, the rainfall has
lowered high temperatures today across Louisiana, though it remains
in the 90s across coastal Mississippi due to less rainfall coverage
up to now. POPs areawide will drop tonight as we lose diurnal
heating, though will remain higher along the immediate coast where
CAPE does not diminish. But with the synoptic lift still in place,
POPs will remain moderate even overnight. Despite the upper low
drifting south tomorrow, even higher POPs are anticipated tomorrow
as a surface front makes its way southward and slows down or even
stalls across our area and a shortwave tracking southward into the
lower Mississippi Valley. Both will sustain synoptic scale lift,
especially as low-level flow moves perpendicularly into the surface
front. Max temperatures tomorrow are expected to be in the upper
80s, but could reach 90 deg F in some spots where convection, or at
least increased cloud cover due to convection, reaches later. This
is slightly below the climatological mean for mid-July high
temperatures, so the heat advisory routine is being put on pause for
now. A piece of the shortwave is expected on model guidance to
linger across east Texas into Saturday, which will keep POPs high
then as well as the front meanders across the CWA. The same logic
applied for tomorrow`s forecast will be used for Saturday`s
forecast, although initiation may be slightly later in the day
whilst we are in an NVA regime behind the mid-level shortwave.
Accordingly, the WPC has placed us in a Marginal Risk for excessive
rainfall for the entire short-term period (and beyond).

As we`ve seen today across the area, mainly in metro New Orleans,
flash flooding will be the primary concern. PWATs near 2.0" will
create efficient rain rates that, if combined with training or
stationary cells, can cause flooding in a short period of time.
Strong winds will also be possible with these storms, especially if
they form into a QLCS like they did earlier near Baton Rouge. More
discrete and intense cells may produce small hail, though freezing
levels are not very low and will keep this threat at bay, and the
overall severe risk is slim due to minimal vertical shearing.
Rainfall totals are a challenge to pin down for events such as this
where initiation is somewhat random and dependent on mesoscale
boundaries that CAMs cannot accurately depict, but expect an average
of an additional 1-2" areawide. That being said, as we saw today and
countless times in the past, some areas could see significantly
higher in a short period of time. At least it`s cooler!

Dolce

&&

.LONG TERM...
(Saturday through Wednesday night)
Issued at 255 PM CDT Thu Jul 18 2024

More of the same continues through the end of the weekend through
early next week. After a shortwave enters and exits the area on
Friday, we enter more of a persistence pattern with daily chances
of diurnally driven showers and storms, with storms
overnight/morning hours on the coast then inland during the
afternoon and evening hours.

Very high PW values in excess of 2.0 in+ will contribute to the
extremely efficient rainfall rates again in the upcoming days.
CAPE is a little more modest for the area (1k-2k J/kg) but still
sufficient for thunderstorm development. However there is very
little to no shear or winds to steer any thunderstorms so there is
some concern for flash flooding, especially places that have had
repeated rounds of convection. It`s not quite widespread enough to
issue a flood watch, but definitely isolated/localized flash
flooding is possible the next few days.

The one good thing out of this is with bkn/ovc sky coverage and
high PoPs will limit the heat in the area, so no concerns with
heat at least. -BL

&&

.AVIATION...
(00Z TAFS)
Issued at 645 PM CDT Thu Jul 18 2024

At forecast issuance time, convection had departed all terminal
areas, and will not carry as prevailing condition. KMCB had IFR
ceilings at issuance time, with VFR at all remaining terminals.
May be some brief MVFR ceilings this evening, but likely to become
more widespread around sunrise Friday, with areal coverage of SHRA
increasing from the south at that time. Expect all terminals to
see at least brief direct impacts from TSRA during the afternoon
hours on Friday. IFR or lower visibilities and MVFR ceilings
likely at that time. Wind gusts to 30 to 40 knots wouldn`t be out
of the question, but confidence in those occurring isn`t high
enough to include in a TEMPO at the end of the forecast period.
Any significant threat of convection should begin to wind down
around 00z Saturday.

&&

.MARINE...
Issued at 255 PM CDT Thu Jul 18 2024
Diurnally driven showers and thunderstorms, with a few capable of
waterspouts, are expected at least the next few days. Winds and
waves outside of any convection will be generally light at 5-10
kt out of the southwest to southeast.
-BL

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  70  85  71  87 /  60  90  60  90
BTR  75  90  76  91 /  60  90  60  80
ASD  74  88  75  90 /  70  90  80  90
MSY  77  88  77  90 /  60  90  70  90
GPT  75  87  76  88 /  60  90  80  90
PQL  75  90  75  91 /  60  90  80  90

&&

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

$$

SHORT TERM...HD
LONG TERM....BL
AVIATION/UPDATE...RW
MARINE...BL