Area Forecast Discussion
Issued by NWS Lake Charles, LA

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FXUS64 KLCH 270901

Area Forecast Discussion
National Weather Service Lake Charles LA
401 AM CDT Tue Jul 27 2021

.SHORT TERM [Through Thursday night]...

As happens sometimes with the northeast flow aloft and a very
muggy atmosphere, thunderstorms develop late in the day then keep
going into the overnight. Shower activity over land has been
decreasing, with thunderstorm activity continuing to ride along
the coast and coastal waters of southwest Louisiana.

Analysis shows that the center of the upper level ridge is now
back over the mountain west. Meanwhile, an upper level low is
noted over the western Gulf of Mexico just off the lower Texas
coast. This is creating a bit of a shear axis over the forecast
area with the east-northeast flow aloft that will continue through
the day.

Also, latest LAPS analysis shows a moist air mass in place with
PWAT values between 2.0 and 2.2 inches, which is between the 75th
and 90th percentile of SPC climo for the area, as well as mean
layer relative humidity values over 70 percent. These values are
expected to persist through the day today. Therefore, ingredients
are in place that a good bit of shower and thunderstorm activity
should redevelop with daytime heating.

Rain chances for Wednesday and Thursday will depend on a westward
moving inverted trough currently over the southeast Gulf of
Mexico. This system will be near the Louisiana coast on Wednesday
morning. Progs are showing some subsidence and dryness on the west
side of this feature that would affect mainly locations along and
south of the I-10 corridor. PWAT values in that area drop down to
below 1.75 inches, which is below climo norm, with mean layer
relative humidity values at or below 50 percent. However, moisture
values remain high over northern sections of the forecast area.
Therefore, less convection is expected on Wednesday for southern
zones, while high end chance pops will continue for the northern

On Thursday, the inverted trough feature will be moving into the
Texas coast. Therefore, high moisture values will return for the
entire forecast area, and again a good chance for scattered
showers and thunderstorms, especially during the afternoon.


.LONG TERM [Friday through Tuesday]...

At the beginning of the long term period, broad upper level high is
forecast to be centered roughly from the Central Plains southeast
towards the Lower Mississippi River Valley with shortwave troughing
digging into the NE CONUS. At the surface, an area of high pressure
over the NE Gulf of Mexico will yield generally light onshore flow.
This will help keep PWAT values mostly within the upper half of the
IQR for this time of year. With the forecast region remaining on the
southern periphery of the upper high, will likely see some westerly
moving waves of shortwave energy leading to an enhancement of the
diurnal PoP cycle. With the NW half of the forecast area under a bit
more influence/subsidence in association with the upper level high,
a little lower PoPs there in comparison to the remainder of the
region. Similarly, temps in the northern half of the CWA come in a
bit warmer with highs in the mid to upper 90s. That said, the
combination of heat and humidity areawide looks likely to yield
several hours with heat index values rising into the 105-110 range.
While precip placement/coverage and mixing will have some impact on
this, looks to be hot enough you`ll want to take precautions to
abate heat related issues (hydrate, frequent breaks, etc.) if
spending much time outdoors.

Moving into the weekend, a slow amplification of the trough into the
E CONUS is noted, resulting in the SE extent of the upper high to
begin to erode. Over the local forecast area, heights remain fairly
steady state though, so wont see too much of a change to the daily
pattern. Still a continuation of diurnally enhanced scattered
convection and potentially dangerous afternoon heat indices in the
105-110 range.

By Monday into next week, the E CONUS trough continues to amplify
and dig further south. The resulting height falls over the region
lead to a slight uptick in PoPs as well as maybe a slight bit of
relief from the heat as the influence of the ridge wanes. Too far
out and with too much uncertainty to put much confidence behind
it... But, some guidance suggesting trough amplifies enough to push
an uncommon August cold front through on Tuesday. For now, something
to watch in upcoming forecasts, since if it does materialize, it
would have noticeable impacts to the PoPs/temps.




A weak pressure pattern will continue today and tomorrow that will
keep mainly light and variable winds, along with low seas. A
surface high over the northeast Gulf will build into the coastal
waters by the end of the week. This will allow for a more
southerly flow to develop over the coastal waters, although wind
speeds will remain on the light side.

Main issue for the coastal waters will be scattered showers and
thunderstorms through today with locally higher winds and seas,
and a concern for frequent cloud to water lightning.

Less thunderstorm activity is expected on Wednesday before
thunderstorms increasing again on Thursday.



AEX  96  76  94  76 /  60  30  50  10
LCH  93  76  93  77 /  50  20  40  10
LFT  94  75  93  76 /  50  30  40  10
BPT  94  75  93  76 /  40  30  30  10



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