118
FXUS64 KLCH 191755
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
1255 PM CDT Fri Jul 19 2024

...New AVIATION...

.SHORT TERM...
(Today through Sunday night)
Issued at 315AM CDT Fri Jul 19 2024

Latest look at observations, satellite, and radar, a surface
frontal trough looks to be just along the northern border of the
forecast area with cyclonic flow associated with a mid level low
over central Louisiana. Latest upper air sounding from KLCH and
LAPS analysis shows a very moist air mass in place with PWAT over
2 inches across the forecast area and around 2.15 inches, which is
the 90th percentile of SPC daily climo, near the surface front
and the low. Scattered showers and a few thunderstorms are noted
also near the frontal boundary and low with moderate to
occasionally heavy rain.

The frontal trough and mid level low look to gradually move to the
southeast for the remainder of today into Saturday before the
frontal boundary stalls. With the high moisture, weakness aloft,
and surface moisture convergence along the front, widespread
showers and thunderstorms are expected to develop with best
concentration near the frontal boundary that will also gradually
move to the east-southeast. With PWAT values over 2 inches and
mean relative humidity values over 70 percent, some high rain
rates will be possible.

With slow movement of storms along the boundary, and the
possibility of some cell mergers or training, to go along with
the high rainfall rates, some locally excessive rainfall in a
short period of time may cause drainage issues leading to a flood
potential for streets and urban poor drainage areas, and a
Marginal Risk Potential (risk level 1 out of 4) or between a 5 to
14 percent chance of seeing flash flooding, will be outlined for
the entire area through early afternoon, switching more to the
eastern portions of the forecast area later this afternoon into
Saturday.

The frontal boundary loses its identity on Sunday. However, the
weakness will remain aloft, and a deeper southerly flow begins to
establish itself that will again bring in PWAT values over 2
inches. Therefore, with daytime heating, widespread showers and
thunderstorms are expected to develop, with again a potential for
torrential downpours that may bring about a localized flood risk.

With clouds and convection, high temperatures will be a little
below normal and keep max afternoon heat index values below 100F
for the most part.

Rua

&&

.LONG TERM...
(Monday through Friday)
Issued at 315 AM CDT Fri Jul 19 2024

The wet pattern is looking like it will persist into next week.

The consensus of guidance is still 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, along with occasional short waves or vort maxes
to enhance shower and storm activity. Although it is tough to time
these features, so will just broad brush high pops each day.

Plenty of Gulf moisture will be over the forecast area for 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 through Thursday period, there is some
concern that the excessive rainfall and flood potential could
increase. 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 14k to 16k 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 expected 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 with daily highs below normal and max
heat index readings mainly at or below 100 degrees for next week.

Rua

&&

.AVIATION...
(18Z TAFS)
Issued at 1255 PM CDT Fri Jul 19 2024

Local 88Ds show the convection which has been moving ewd across
the forecast area is now past the Atchafalaya with CAM guidance
showing just spotty activity the rest of the day...am carrying
PROB30s for later this afternoon to account for possible
redevelopment with heating. Expecting some additional late night
maritime convection once again tonight which will spread inland,
particularly by the mid-morning hours for the srn terminals.
Otherwise, VFR conditions should prevail outside of convection.

25

&&

.MARINE...
Issued at 315 AM CDT Fri Jul 19 2024

A frontal trough will near the coast today into Saturday from the
north and stall. With a weak pressure pattern, winds will mainly
be light and variable with low seas. The only caveat will be winds
and seas higher near any thunderstorms that develop as a weakness
aloft and a very moist air mass will combine for chances of
showers and thunderstorms.

The frontal trough will wash out on Sunday with a surface ridge
being reestablished across the northern Gulf of Mexico from the
western Atlantic. This will help provide mainly light southerly
winds to go along with low seas into next week. High chances of
showers and thunderstorms will continue over the coastal waters
and once again marine interests need to be on the lookout for
higher winds and seas along with occasional cloud to water
lightning with the storms.

Rua

&&

.PRELIMINARY POINT TEMPS/POPS...
AEX  86  70  90  71 /  70  30  50  30
LCH  89  75  88  75 /  50  50  80  60
LFT  89  76  90  76 /  70  60  80  50
BPT  91  74  91  75 /  50  40  70  40

&&

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

$$

SHORT TERM...07
LONG TERM....07
AVIATION...25