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000
FXUS64 KLCH 121800
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
100 PM CDT Wed Aug 12 2020

.DISCUSSION...
18Z TAFS

&&

.AVIATION...
A deep column of moisture wrapping around the eastern periphery of
an upper level ridge centered over Texas will allow for
scattered shower and thunderstorm development this afternoon with
LFT and ARA most likely to see impacts. Away from storms, VFR
conditions will prevail along with light southwesterly winds.

Convection will diminish around sunset this evening with VFR
conditions prevailing overnight through Thursday morning.

Jones

&&

.PREV DISCUSSION... /issued 1128 AM CDT Wed Aug 12 2020/

DISCUSSION...
Wx map shows surface high pressure ridging across the Gulf. Radar
continues to show large cluster of showers and thunderstorms
across S AR/N LA. While this activity is not expected to reach our
area, the outflow boundary may reach the area, generating
additional SHRA/TSRA along with afternoon heating. Bumped up the
chances of precipitation a bit for this afternoon.

Temperatures and heat index values will be the other issue this
afternoon. Expecting mid 90s across SE TX, coupled with dewpoints
in the mid to at times upper 70s, will give heat index values
108-111 during the afternoon hours. For this, issue a Heat
Advisory through 7 PM. Elsewhere, heat index values expected to
range 105-107, and may briefly touch 108-109 for an hour, but not
long enough to warrant expanding the heat advisory eastward at
this time.

DML

PREV DISCUSSION... /issued 649 AM CDT Wed Aug 12 2020/

DISCUSSION...
For the 08/12/20 1200 UTC TAF package.

AVIATION...
Isolated showers, and even a brief thunderstorm, noted streaming
north across parts of the Gulf and the immediate coastal
counties/parishes. None of this activity is affecting a terminal,
with VFR prevailing all sites. Saw little reason to deviate much
from the forecast inherited last night, with prevailing VFR
through the period and VCTS for all terminals mid afternoon to
early evening.

13

PREV DISCUSSION... /issued 440 AM CDT Wed Aug 12 2020/

SYNOPSIS...
Latest UA analysis and WV imagery shows ridging aloft centered
acrs W TX and southern NM/AZ and northern Mexico. The ridge axis
extends east toward the NW Gulf coast, while a shortwave trough
approaches the lower MS Valley, eroding the eastern end of the
ridge. At the sfc, high pres continues to ridge acrs the northern
Gulf providing a warm and humid onshore flow. Temperatures acrs
the region are in the upper 70s/around 80.

KLCH radar remains generally quiet attm with just a few isolated
showers developing over the nearshore waters. Zooming out to the
regional mosaic, a complex of storms is noted acrs SE OK and much
of southern AR associated with the shortwave trough, with additional
convection acrs SE LA.

24

DISCUSSION...
Ridging should continue to prevail today acrs TX and far western
LA, although the shortwave north of the area will continue to
weaken the eastern periphery of the ridge, allowing for a little
more sctd convection acrs the Atchafalaya Basin and lower Acadiana
during the aftn. As can be typical with mesoscale convective
systems north of the area, there is the potential of an outflow
boundary emanating southward from the complex during the day,
resulting in the development of a band of showers or storms that
moves into our northern zones (and sometimes moves as far as south
as the I-10 corridor). While this scenario cannot be ruled out
entirely, CAM guidance has downplayed the possibility of anything
more than widely sctd showers or storms acrs SE TX and W/SW LA
today, and the current fcst reflects this.

Otherwise, expect partly cloudy skies today, which will allow
temperatures to warm into the lower to middle 90s. Southerly
winds will keep dewpoints in the lower 70s through the day, and
this will produce heat indices or apparent temperatures between
102 and 108 degrees during peak heating this aftn. For the most
part, heat indices should remain below advisory criteria today,
but a few isolated locations in SE TX could briefly meet or exceed
the 108 degree threshold for an hour or two. Given the brevity
and minimal coverage of these higher values, opted not to issue
heat advisory at this time.

From Thursday through the weekend, the upper ridge will gradually
retrograde over the desert SW, leaving a trough/weakness aloft
along and east of the lower MS Valley. Moisture will deepen acrs
the region with PWATs ranging from 1.7 to 2 inches. This, along
with limited capping aloft, will result in more sctd diurnally
influenced convection acrs the area, not atypical for this time of
year. The highest chcs are still expected to be acrs the eastern
zones, with more widely sctd showers and storms further west.

By early next week, the pattern aloft becomes more amplified as a
northern stream shortwave digs acrs the Great Lakes into the Ohio
Valley, deepening the trough over the eastern CONUS. This will
help to usher a frontal boundary into the region Monday into
Tuesday. Convective coverage is expected to increase along and
ahead of the boundary as it encounters the warm and moist airmass
acrs the region. The front looks to bring a slightly cooler and
drier airmass, should it make it through to the coast, with
dewpoints falling into the 60s. NBM temperatures indicate high
temps in the upper 80s/around 90 for Wednesday (just beyond the
fcst period), with lows that morning in the upper 60s to lower 70s.

Outside of the possible frontal passage toward the end of the
period, no significant temperature fluctuations are expected
through early next week, with daily highs and lows mostly near
mid August climatological normals. With dewpoints mostly in the
70s each day, heat index values will generally range from 102 to
108 degrees during peak heating. The likeliest areas to reach heat
advisory levels are expected in SE TX, and advisories may become
warranted should apparent temperatures of 108 or higher become
more extensive. Either way, individuals are encouraged to use
caution during outdoor activities.

24

MARINE...
Persistent high pres ridging acrs the northern Gulf will maintain
a light to sometimes modt onshore flow through the period. Winds
will remain around 10 KT or less, with seas of 1 to 2 feet, so no
advisory or caution flags are anticipated. Showers and tstms are
expected to become more sctd over the next few days, especially
along and east of Vermilion Bay. A typical summertime pattern is
expected, with convection developing during the late night/early
morning hours, and spreading inland acrs the coastal areas after
sunrise. Winds and seas could be briefly higher near the storms,
along with occasional cloud to water lightning.

24

&&

.PRELIMINARY POINT TEMPS/POPS...
AEX  75  96  75  96 /  20  30  10  30
LCH  77  93  78  93 /  10  30   0  30
LFT  77  94  77  93 /  20  40  10  40
BPT  77  93  78  93 /  10  20   0  20

&&

.LCH WATCHES/WARNINGS/ADVISORIES...
LA...None.
TX...Heat Advisory until 7 PM CDT this evening for TXZ180-201-215-216-
     259>262.

GM...None.
&&

$$


AVIATION...66