536
FXUS64 KLCH 171800
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
100 PM CDT Wed Jul 17 2024

...New AVIATION...

.UPDATE...
Issued at 706 AM CDT Wed Jul 17 2024

Basis latest upper air sounding data illustrating a few layers of
lowered RH being entrained from the NW into the mid levels, POPS
have been adjusted for interior SETX and SWLA to reflect decrease
chances of morning precipitation. Isolated to scattered
convection remains in the forecast throughout the mid-afternoon
with favorable lapse rates of 7 deg C / km above 3km AGL and
sufficient surfaced based instability.

30

&&

.SHORT TERM...
(Today through Friday night)
Issued at 259 AM CDT Wed Jul 17 2024

Showers and storms are shifting onshore through the morning and mid
afternoon hours under a slack high pressure regime locally across
SETX and SWLA. An upper level low over SETX will continue to meander
SW along the coast of Texas. This feature will exhibit localized
speed divergence and lift aloft allowing the moist marine
environment with southerly flow to enhance shower / storm activity
throughout today. Guidance trims back the POPS to more isolated
chances by the evening hours as much of this convection has surface
based components that will be suppressed by latent heat released in
the low level environment basis forecast sample soundings. In
between showers / storms where possible breaks in cloud cover, many
locations will see highs the upper 80s to lower 90s as well as on
Thursday.

The upper level feature begins to fill and weaken while shifting SE
into the western Gulf of Mexico where it will open and merge with
troughing along the northern portions of the Gulf of Mexico.
Meanwhile a downstream shortwave associated with extensive frontal
boundary will continue with shift toward the Canadian Maritimes /
Gulf of Maine throughout the day. Trailing from the surface low in
that region will be that cold front boundary curving SW across
Appalachia NETX where a secondary sfc trough will deepen to further
enhance the baroclinic environment along SETX and SWLA priming the
area for more rainfall. Do note, forecast soundings during the
period indicate PWATs measuring in excess of 2.00" at times.
Therefore, localized flash flooding starting with low lying and
urban areas is an impact to monitor through the Friday morning
hours. However, an inhibiting factor will be the limited MLCAPE
which trends further up in the lower troposphere during the
nocturnal hours. Highs Friday will trend little cooler with the
frontal boundary of the aforementioned pattern to the north of the
area will begin to slow along the Gulf Coast, becoming stationary.
Southerly low level flow will continue to abut this boundary as a
secondary shortwave from the northern stream enhances upper level
divergence over the SECONUS helping reform the boundary northward
into early Saturday morning where further shower and storms are
favorable.

Kowalski / 30

&&

.LONG TERM...
(Saturday through Wednesday)
Issued at 259 AM CDT Wed Jul 17 2024

A wet pattern setting up for the long term.

Consensus shows a surface frontal boundary will be stalled over the
forecast area as the period begins that will start to wash out late
in the weekend. A moist air mass will be in place over the forecast
area during the weekend. Frontal convergence, along with a weakness
aloft, will work with the moisture to produce widespread shower and
thunderstorm activity.

PWAT values over the weekend will be near the 90th percentile of
daily SPC climo which is 2.15 inches. 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, that should mean slow moving convection that will make
for 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, some drainage issues may
come about for streets and urban areas. Therefore, WPC has outlined
the 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.

Early next week the forecast area will continue have a weakness
aloft between an upper level trough extending from the Great Lakes
down into Texas, and the sub-tropical ridge to the east. Meanwhile.
a deeper south flow around the sub-tropical ridge will bring a surge
of highly anomalous moist air into the region, with PWAT values well
over the 90th percentile level and over 2.25 inches. 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, then the excessive rainfall and flood potential
risk will be extended into early next week.

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 Saturday into early next week.

07/Rua

&&

.AVIATION...
(18Z TAFS)
Issued at 100 PM CDT Wed Jul 17 2024

Local 88Ds show diurnal convection gradually increasing in
coverage while also spreading nwd...with this trend expected to
continue through the afternoon, have tried timing each of the
terminals accordingly. Otherwise, VFR conditions should prevail
through the period per forecast soundings...any terminals which
receive rainfall today could see the potential for some light fog
towards sunrise, but will allow later issuances the chance to
better define such chances. Winds will remain light and somewhat
variable with high pressure prevailing.

25

&&

.PRELIMINARY POINT TEMPS/POPS...
AEX  96  73  92  71 /  40  20  80  60
LCH  91  77  91  74 /  50  30  80  70
LFT  93  78  92  76 /  60  30  90  60
BPT  93  76  91  74 /  50  20  70  70

&&

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

$$

SHORT TERM...30
LONG TERM....07
AVIATION...25