Area Forecast Discussion
Issued by NWS Lake Charles, LA

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686
FXUS64 KLCH 222035
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
335 PM CDT Mon Apr 22 2019

.DISCUSSION...

Short Term [This Evening through Tuesday]

This afternoon`s surface analysis indicates a broad area of 1020
hPa high pressure extending along the Appalachian Mountains down
into the Gulf Coast. Meanwhile a series of weak surface cyclones
extend across the central and southern Plains. The pressure
gradient across the CWA is resulting in SE winds across the region
this afternoon. These winds are advecting greater moisture into
the region which has resulted in a greater coverage of fair weather
clouds.

This same surface pattern is expected to continue tomorrow as a
cutoff low at 500 hPa centered over the southwest CONUS slowly
digs southeastward. Therefore, similar weather to today is
expected tomorrow with partly to mostly cloudy skies and high
temperatures in the upper 70s to near 80.

Long Term [Wednesday through Sunday]

Starting Wednesday, the upper level trough over the southwest will
begin to eject into the southern Plains. This will support the
development of a surface cyclone over south-central Texas which
will progress east-northeastward along the Gulf Coast through
Friday. As a result, precipitation chances return to the forecast
during this time frame.

The majority of the day Wednesday looks dry with convection
most likely entering southeast Texas after 7 PM Wednesday. The
majority of the showers and thunderstorms are expected to move
through the region overnight Wednesday through late Thursday
afternoon. The system will exit the region Thursday evening and
bring an end to the precipitation.

Return flow in advance of this system will result in a
conditionally unstable atmosphere setting up over the region with
potentially up to 1000-2000 J/kg SBCAPE. Meanwhile, 0-6 km bulk
shear is forecast to be in excess of 40 knots which in combination
with the instability will support at least some threat for severe
weather. The potential for severe weather and expected hazards
will largely be dependent on the timing of the upper level trough.
As a result, SPC does not currently have the region highlighted
in a threat area. However, it is likely that at least some risk
area will be added into the new Day 3 outlook issued later
tonight.

While there is some uncertainty with regards to severe weather,
confidence is increasing that there will be a threat for heavy
rainfall and flash flooding from this system. PWAT values are
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. The sheared nature of
the upper level trough will result in deep shear vectors being
aligned roughly parallel to the surface front which will support
upscale growth and the potential for storms to train over the same
area. All these factors combined point to a potential for heavy
rainfall and flash flooding from Wednesday night through Thursday
evening. Currently, forecast rainfall totals during this timeframe
range from 1"-3". However, some of the individual models are
indicating the potential for localized amounts of 4"-6+" with the
heavier convection.

Given the uncertainty with this system and how poorly guidance has
handled events over the past few weeks, continue to monitor the
forecast for late Wednesday into Thursday through the upcoming
forecast cycles. Hopefully guidance will have a better handle as
it gets closer to Wednesday/Thursday and the forecast will be more
accurate than it has recently been.

Beyond Friday, predominately zonal flow is forecast to be in place
over the eastern two thirds of the CONUS through the weekend. This
will result in dry conditions and some of the first hints of a
transition to summer with daily highs in the mid to upper 80s and
lows in the mid to upper 60s.

&&

.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. 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  58  78  59  80 /   0   0  10  20
LCH  63  77  64  79 /   0  10  10  20
LFT  59  79  62  81 /   0   0   0  20
BPT  65  77  65  78 /   0  10  10  20

&&

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

$$

PUBLIC...26



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