Area Forecast Discussion
Issued by NWS Lake Charles, LA

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FXUS64 KLCH 201705
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
1105 AM CST Sat Jan 20 2018

.DISCUSSION...
12Z Taf issuance.

&&

.AVIATION...
Area of showers over Central and South Central Louisiana moving
eastward with the upper level disturbance, otherwise, VCSH
expected this afternoon. Intermittent MVFR ceilings this afternoon
will become prevailing by 00z, with intermittent IFR ceilings/visibilities
towards daybreak. Possible LIFR ceilings/visibilities at BPT/LCH
towards daybreak with the expected marine fog forming offshore,
but not expecting widespread coverage inland.

DML

&&

.PREV DISCUSSION... /issued 925 AM CST Sat Jan 20 2018/

UPDATE...The majority of the showers are moving east/northeast
across Acadiana this morning with lesser activity noted westward.
Rain chances will continue to decrease through the day as a short
wave moves by. This is in line with the previous forecast an no
changes are needed at this time.

PREV DISCUSSION... /issued 552 AM CST Sat Jan 20 2018/

DISCUSSION...
20/12Z TAF Issuance.

AVIATION...
Shortwave energy aloft is producing clouds and sctd -SH over the
area. Cigs this morning range from intermittent MVFR at
BPT/LCH/AEX to prevailing VFR mid-level cigs at LFT/ARA. MOS
guidance and fcst soundings indicate MVFR cigs increasing and
bcmg more prevalent from west to east today, with VCSH gradually
tapering off by 21/00Z. Cigs are expected to lower this evening,
bcmg IFR by 06Z with patchy fog expected overnight. Southeasterly
winds 7-12 KT will decrease slightly during the evening.

24

PREV DISCUSSION... /issued 420 AM CST Sat Jan 20 2018/

SYNOPSIS...
Surface high pressure is now centered over the southern
Appalachians and this is allowing more of an east to southeast
flow in the low levels across the forecast area, and with it,
milder temperatures and higher moisture values than at this time
yesterday. Water vapor imagery shows a short wave moving across
the forecast area, and this is helping to provide scattered mainly
light showers.

Rua

DISCUSSION...
In the short term the upper level short wave will move gradually
east providing scattered light rain showers into the afternoon
hours.

Meanwhile, short wave energy moving eastward this weekend will
help form low pressure and a developing storm system over the
Rockies. This system will move east-northeast across the Upper
Midwest and Great Lakes through Monday. A trailing cold front from
this system will move across the forecast area early Monday
morning.

Ahead of the front, southerly flow between high pressure over the
Southeast US and the developing low over the Rockies will
increase. The increase in southerly flow will push a warm front
through the forecast area with an increase in temperatures and
humidity values by tonight.

Best chance for rain will be ahead of the front Sunday night into
early Monday morning. Southerly flow of 40 plus knots is noted
between 85H-70H during this time that will bring plenty of
moisture into the forecast area, with PWAT progged to be over 1.25
inches, which is over the 75th percentile, and Mean RH over 70
percent. Therefore, scattered shower activity will develop late
Sunday into Sunday night that will eventually form into a linear
band of convection.

The increasing low and mid level wind fields will provide good
bulk shear numbers between 0-6km of 40 to 50 knots. That along
with favorable lapse rates, should be able to get a few
thunderstorms embedded in the showers. Just how much thunderstorm
coverage and intensity will depend on the low level instability.
Timing of event, during the night and early morning, along with
cool Gulf water temperatures (currently in the upper 40s to lower
50s) may keep instability on the low side, with progs showing best
CAPE values in the mixing layer and at the surface below 500
j/kg. It should be noted that SPC does have the lower Acadiana
portion of the forecast area in a Marginal Risk for Day3 as there
is a little better instability in that region after 12Z Monday.

Cooler and drier air will then move in behind the front by Monday
afternoon. Air mass is not of Arctic origin and more of a modified
continental, so not expecting any below freezing temperatures,
just seasonally cool.

Another front at the end of the forecast period to bring the next
chance of rain next weekend.

Rua

MARINE...
Moderate southerly flow will persist over the weekend as high
pressure moves to the Southeast US and low pressure develops over
the Rockies. The southerly winds will bring in a warmer and more
moist air mass over the Gulf waters, and this will bring the
possibility of patchy sea fog tonight into Sunday.

A cold front will move across the coastal waters early Monday
morning. Showers and a few thunderstorms will develop ahead of the
front, with some of the storms producing gusty winds. Moderate
offshore flow will then develop by Monday afternoon behind the
front and persist through mid week.

Rua

&&

.PRELIMINARY POINT TEMPS/POPS...
AEX  67  55  73  56 /  40  20  30  80
LCH  68  57  73  57 /  30  20  20  80
LFT  67  56  73  59 /  40  10  10  60
BPT  68  58  73  56 /  30  20  20  80

&&

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

$$


AVIATION...08



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