475
FXUS64 KLCH 180859
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
359 AM CDT Thu Jul 18 2024

...New SHORT TERM, LONG TERM, AVIATION...

.SHORT TERM...
(Today through Saturday night)
Issued at 353 AM CDT Thu Jul 18 2024

An upper level trough shifts off the SETX Coast into the western
Gulf.  Concurrently, a shortwave trough with positive tilt further
upstream over the central Plains will continue to amplify toward the
ARKLAEX and Mississippi Valley into Sunday morning. Together, both
features develop a series of minor perturbations in the pressure
pattern aloft to sweep through the area, thus providing multiple
rounds of Isolated to periodically widespread showers and storms
through Sunday. In addition the frontal pattern along with increased
cloud cover will trend down daytime high temperatures toward mid
upper 80s through the start of the weekend. Should be noted, that
sfc  3km moisture transport continues to remain from the Gulf /
Caribbean driven easterlies which are forecast to develop a healthy
moisture jet keeping the pattern fairly we throughout the remainder
of the short term.  That said, despite the influx of tropical
moisture, per most recent guidance from NHC there is no tropical
development forecast to develop in the next 7 days.

Zooming in to the weather at hand, a southward moving cold frontal
boundary over central LA continues to stall, becoming stationary
along the SETX and SWLA Gulf Coast briefly. Last nights evening
sounding data calculates PWAT of 1.88 which has been congruent with
prior days forecast suite. With that in mind, northern portions of
SETX and SWLA are in a Slight Risk (level 2 of 4) for excessive
rainfall with the greater surrounding counties and parishes under a
marginal risk(level 1 of 4).  The stationary front will be the focal
point for more widespread and heavier rainfalls to occur throughout
today as it shifts southward. By tonight the front become stationary
near the coast while the aforementioned shortwave amplifying south
continues to shift east toward central AR. Additional speed
divergence and vorticity are generated along central and southern
portions of LA including SETX counties, therefore another night of
nocturnal rainfall will occur into Friday morning. Here, the
stationary front hangs along the coast remaining the focus area of
thunderstorm genesis throughout the day. That said, periodic breaks
to allow broken cloud cover is not out of the question. By Saturday
morning, the parent shortwave shifts eastward over the TN while
keeping a positive tilt toward the LA Gulf Coast lifting the
boundary north again toward the ARKLTEX region. Upstream, another
shortwave trough begins to deepen south of the central plains
developing a weak surface trough over southern AR. Referring back to
the earlier mentioned sfc- 3km moisture transport strengthening
across the Gulf into the interior regions of TX / LA /MS, we
continue to stay the course for further rounds of precipitation
continuing into Sunday morning.

Kowalski / 30

&&

.LONG TERM...
(Sunday through Thursday)
Issued at 353 AM CDT Thu Jul 18 2024

Still looking like a rather wet pattern setting up for the long term.

Consensus of guidance is showing an upper level trough will be
located from the Great Lakes into central Texas. Meanwhile, the Sub-
Tropical Ridge will be centered over the western Atlantic off the
east coast of Florida and the southeast US coast. This will allow
for a weakness aloft to persist over the forecast area. This will
likely provide little inhibition to get convection going.

Plenty of Gulf moisture will be over the forecast area for Sunday
into Monday with PWAT values between 2 and 2.15 inches which is
between the 75th and 90th percentile of daily SPC climo. Mean
relative humidity values from 100H-50H will be over 70 percent, so
the convection will have a chance to be efficient precipitation
producers. Mid level winds look to be light, and progged storm
motion is around 10 knots. Therefore, slow moving convection with
high rainfall rates could bring some drainage problems, not to
mention the potential for mesoscale boundary collisions and cell
mergers that will enhance rainfall with the result torrential
downpours.

With the potential for high rain rates that could provide some
drainage issues for streets and urban areas, WPC has outlined
portions of the forecast are in a Marginal Risk Potential (risk
level 1 out of 4) for Excessive Rainfall that may lead to flash
flooding or the flood potential between 5 to 14 percent.

As we get into Tuesday and further into the middle part of the week,
no pattern change is noted. In fact, southwest flow is progged to
increase ahead of the upper level trough that will increase surging
East Pac moisture into the forecast area. Meanwhile, deep southerly
flow around the sub-tropical ridge will bring surging moisture with
origin from the northwest Caribbean and southwest Gulf of Mexico.
The convergence of these moisture plumes will make for a tropical-
like air mass with highly anomalous moist air over the forecast
area. PWAT values well over the 90th percentile level and nearing
max moving levels between 2.25 and 2.5 inches. The mean relative
humidity in the 100H-50H layer is progged to be over 80 percent with
warm cloud layer depth in the 13k to 15k foot range. Therefore,
convection will likely be of the warm process highly precipitation
efficient variety, which again means the likelihood of torrential
downpours with high rain rates in a short period of time. If this
scenario continues, and antecedent conditions become more moist from
the expect rain over the weekend, then the flood potential risk may
increase. However, still plenty of time to watch to see if this
scenario becomes more likely.

With the expected cloud cover and widespread convection, the heat is
expected to be kept in check somewhat with max heat index readings
mainly at or below 100 degrees for Sunday into next week.

07/Rua

&&

.AVIATION...
(06Z TAFS)
Issued at 353 AM CDT Thu Jul 18 2024


SHRA and TS are expected throughout the day over greater portions of
SETX and SWLA while under light due southerly flow outside of TS. A
frontal boundary is expected shift southward toward the Coast of
SETX and SWLA initiating a heavier segmented line of TS along to and
below I-10 corridor during the late afternoon to early evening
hours. Thus, while VFR conditions may prevail for periodically,
reduced ceilings and occasionally VIS near TS will limit trend
conditions MVFR by and large with periodic / brief IFR or LIFR
conditions near more robust convection.

30

&&

.MARINE...
Issued at 335 PM CDT Wed Jul 17 2024

Not expecting the need for any headlines on the CWF over the next
several days.

25

&&

.PRELIMINARY POINT TEMPS/POPS...
AEX  89  71  86  70 /  70  70  80  30
LCH  90  74  88  75 /  70  80  80  70
LFT  92  76  89  76 /  90  70  90  60
BPT  91  74  90  74 /  70  70  80  60

&&

.LCH WATCHES/WARNINGS/ADVISORIES...
LA...None.
TX...None.
GM...None.
&&

$$

SHORT TERM...30
LONG TERM....07
AVIATION...30