Area Forecast Discussion
Issued by NWS Lake Charles, LA

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000
FXUS64 KLCH 240137
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
837 PM CDT Tue Apr 23 2019

.UPDATE...A few sprinkles have been noted over the region through
the past several hours and will continue through midnight. Any
accumulations are expected to be trace amounts.

The forecast remains on target and no changes are needed at this
time.

&&

.PREV DISCUSSION... /issued 633 PM CDT Tue Apr 23 2019/

DISCUSSION...
For the 24/00Z TAF Issuance.

AVIATION...
Low level southerly flow will continue during the period with an
increase in low level moisture. Time heights all show lowest
layers will favor the development of a mainly MVFR cloud deck
between 1500 and 2500 feet during the evening hours at KBPT and
during the overnight at the remainder of the terminals. Although
surface winds will likely become light and variable overnight,
boundary layer winds stay up enough and extensive cloud cover may
limit diurnal cooling. Therefore, low ceilings were favored rather
than significant fog.

Rua

PREV DISCUSSION... /issued 406 PM CDT Tue Apr 23 2019/

SYNOPSIS...

A low pressure system will move across the region late Wednesday
evening through Thursday. This will bring a chance of scattered
severe weather and flash flooding. High pressure will build in
behind the system on Friday resulting in a period of drier and
warmer weather that will continue into early next week.

DISCUSSION...

Short Term [This evening through Thursday]

Beginning tomorrow, a cutoff upper level low over northern Mexico
is expected to eject east-northeastward across the Lower
Mississippi River Valley into the East Coast. This will support
the development of a surface cyclone over south-central Texas
which will progress east-northeastward along the Gulf Coast
through late Thursday. As a result, precipitation chances return
to the forecast during this time frame. The system will exit the
region Thursday evening and bring an end to the precipitation.

Compared to yesterday, model guidance is beginning to point at a
slightly better chance for severe thunderstorms to occur during
the late Wednesday evening through Thursday timeframe. In
particular, some of the 12Z Convection Allowing Models were
developing a line of strong thunderstorms with bowing segments
that moved across the CWA overnight Wednesday. 1000-2000 J/kg of
SBCAPE in combination with 0-6 km bulk shear in excess of 45 knots
and a strengthening low level jet could certainly support such a
scenario. Therefore, the Storm Prediction Center is now
highlighting a majority of the CWA in a Slight Risk with scattered
severe thunderstorms possible from late Wednesday evening through
Thursday.

With the latest round of model guidance indicating a stronger line
of thunderstorms moving through the area, timing of the system now
looks to be slightly faster than yesterday. Currently, the prime
timeframe for severe weather looks to be as follows: southeast
Texas from 12 AM-6 AM / western Louisiana from 3 AM-9 AM /
Acadiana from 6 AM - 12 PM. There is still some uncertainty with
regards to the timing of this system so continue to monitor the
forecast for updates during the day tomorrow. The main threat will
be damaging winds. However, SRH in excess of 150 m2/s2 along and
ahead of the line of thunderstorm will support the potential for a
QLCS tornado or two.

In addition to the threat for severe weather, there is a Slight
Risk of flash flooding for much of the CWA. PWAT values are still
forecast to increase to 1.7"-2.0" due to a prolonged period of IVT
in excess of 800 kg/ms. Forecast soundings indicate that warm
cloud layers will likely be greater than 3500 m which will
promote efficient precipitation production. While storm speed will
likely be a limiting factor, storm motions similar to the
orientation of the surface front will support at least some
potential for the training of convection. Currently, three hour
flash flood guidance across the region ranges from around 2.5"-5"
and 12Z HREF guidance was indicating maximum precipitation values
of 4"-7" possible. Therefore, will continue the forecast area
average rainfall totals of 1"-3" with localized higher amounts and
flash flooding possible from late Wednesday through the day
Thursday.

The line of showers and thunderstorms should begin exiting the
region by Thursday evening (possibly even earlier if some of the
more progressive guidance proves correct) and bring an end to
precipitation chances by Thursday night.

Long Term [Friday through Tuesday]

On Friday, high pressure will build into the region behind the
area of low pressure resulting in drier conditions. Predominately
zonal flow is forecast to be in place over the eastern two thirds
of the CONUS through the weekend into early next week which should
keep most frontal systems well north of the CWA. Therefore, dry
conditions are expected to persist into the early to middle part
of next week. This drier weather will also produce some of the
first hints of a transition to summer with daily highs in the mid
to upper 80s and low in the mid to upper 60s.

A broad upper level trough is forecast to develop over the central
CONUS by the middle part of next week and result in the next
potential for rainfall. However, there are some disagreements with
regards to both the timing and the amplitude of this upper level
trough. Therefore, PoPs were generally limited to 20% or less at
the end of the long term period.

MARINE...

Onshore flow will remain in place through Wednesday ahead of an
approaching low pressure system. This system will produce
widespread showers and thunderstorms over the coastal waters from
late Wednesday through the day on Thursday. Following the frontal
passage, a modest offshore flow will develop on Friday. Small craft exercise
caution or small craft advisory headlines may be needed at some point
from Wednesday through Friday. Winds and seas are expected to
subside Saturday through the rest of the weekend as high pressure
builds into the region.

&&

.PRELIMINARY POINT TEMPS/POPS...
AEX  60  79  64  75 /  10  10  80  80
LCH  65  78  67  77 /  10  10  80  80
LFT  62  80  67  77 /  10  10  70  80
BPT  66  78  66  78 /  10  20  90  60

&&

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

$$

PUBLIC...05



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