Area Forecast Discussion
Issued by NWS Lake Charles, LA

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000
FXUS64 KLCH 050602
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
1202 AM CST Mon Dec 5 2016

.DISCUSSION...
05/06Z TAF Issuance.

&&

.AVIATION...
Few changes to the 06Z TAFs as patchy -RA and IFR cigs will
persist. More widespread rain and showers, currently developing
acrs TX, will begin reaching TAF sites between 12-15Z Monday.
Periods of light to moderate rain, along with some embedded TSRA,
can be expected through the day as the sfc low and frontal
boundary begin to lift northward in concert with an upper low. Low
cigs will continue through the day with ocnl MVFR/IFR vsbys. Winds
will gradually shift more west to southwesterly after 00Z with
rain tapering off from west to east during the evening as the low
pres system lifts to the NE.

24

&&

.PREV DISCUSSION... /issued 928 PM CST Sun Dec 4 2016/

UPDATE...
Frontal boundary remains stalled over the gulf this evening as
moisture rides up and over. Rains will continue into the
overnight with temps holding around 50 degrees more or less. This
pattern look to finally gets a kick out of the region late
tomorrow. Current zones are fine.

PREV DISCUSSION... /issued 609 PM CST Sun Dec 4 2016/

DISCUSSION...
05/00Z TAF Issuance.

AVIATION...
Deep moisture continues to spread over the region, with lift aided
by a sfc low off the lower TX coast and frontal boundary that
extends northeastward acrs the NW Gulf and an upper low that
continues to spin over northern old Mexico. This is producing
widespread low clouds with prevailing IFR cigs. A swath of -RA/RA
was streaming SW to NE acrs the Acadiana terminals with more
patchy -RA further west. This area of rain is expected to move
east this evening with just some patchy -RA or isltd -SHRA
continuing overnight before another round of more widespread SHRA
moves into the area Monday morning, with TSRA possible near the
southern terminals during the day. IFR cigs are expected to
prevail through Monday with vsbys lowering to MVFR/IFR during
periods of rain. Northeasterly winds around 10 kt will gradually
shift more easterly to southeasterly by midday Monday as the sfc
low begins to move inland acrs SE TX/SW LA.

24

PREV DISCUSSION... /issued 357 PM CST Sun Dec 4 2016/

SYNOPSIS...
Surface analysis shows an quasi-stationary frontal boundary from
along the Southeast Louisiana coast to just off the tip of the
Lower Texas coast. Forecast area has been on the cool side of the
boundary with temperatures staying in the 50s.

Meanwhile...water vapor imagery shows an upper level low that has
been over the Baja area...now moving to the east-northeast into
Northwest Old Mexico. Ahead of this system is an active and very
moist stream of southwesterlies from the East Pacific across East
Texas and through the Gulf South.

Latest GPS-MET Precipitable Water value at the KLCH site is
hanging around 1.6 inches...which is what the value was from the
KLCH 04/12Z upper air launch. This value is much above the norm
for the cool season. The over-riding moisture across the surface
boundary and cool low layer has allowed for a steady light to
occasional moderate rain over the forecast area through the day.
Water vapor imagery shows a deeper moist plume off the Lower Texas
coast where convection has been increasing according to lightning
data and regional radars.

Rua

DISCUSSION...
The upper level low will continue to lift to the east-northeast
reaching the forecast area late Monday. A surface low is expected
to form along the southern end of the stationary front and move in
tandem with the upper level low, and across the forecast area on
Monday Afternoon into early Monday Evening. Forcing and lift will
increase as these systems near the forecast area, with rainfall
rates and intensity expected to increase late tonight and on
Monday...as low level flow above the surface increases. Abundant
moisture again will be transported over top of the front and into
the forecast area. Projected Precipitable Water values are
expected to be between 1.6 and 1.8 inches...which is around twice
the standard deviation of norm...with Mean RH values over 90
percent.

Antecedent conditions are on the wet side from the recent heavy
rainfall...with high ground moisture and elevated flows on local
drainage bayous...creeks...and rivers. Therefore, it will not take
a lot to create potential flood conditions. Additional area wide
rainfall totals look to average 1 to 3 inches, and locally higher
amounts can be expected where elevated convection gets going. The
Weather Prediction Center has the forecast area outlined in a
Moderate Risk of excessive rainfall on Monday, and the current
Flash Flood Watch will be in effect through Monday Afternoon.

Mid level speed max with west to southwest winds between 50 and 70
knots is expected to reach the forecast area on Monday afternoon.
At this time, the surface low will be traveling through the
forecast area along the stalled boundary. Some warm sectoring may
occur in parts of lower Acadiana, although best surface based
instability and CAPE values look to stay offshore. If some of the
storms can become rooted in the surface, there will be a chance
for some damaging wind gusts. There may also be the potential for
some hail storms mainly southeast of an Opelousas to Lake Charles
line, where lapse rates and shear above the surface from speed max
favors it.

Once the upper level trough moves to the east of the forecast area
on Monday Evening, taking the surface low and boundary with it,
drier and more stable conditions will move in.

The next weather story will be the potential for some cold
conditions late in the week. A Polar Canadian surface front is
still progged to move across the forecast area Wednesday Night
into very early Thursday Morning. Some quick return flow moisture
and frontal convergence will allow for a few showers to develop
right along the front.

Some of the coldest air of the season will sill over the Canadian
border and down through the plains into the forecast area...with
Thursday being breezy and chilly. The coldest temperatures look to
be on Thursday Night into Friday Morning...although extended
guidance still differ somewhat in the positioning of the 1040+ MB
surface high...with the GFS over the Ozarks, and the ECMWF over
Central Texas. Superblend numbers have been very consistent with
airmass bringing daytime temperatures some 15F to 20F degrees
below normal, with night time temperatures some 15F degrees below
normal. This will bring freezing conditions to a majority of the
forecast area on Thursday Night into Friday Morning. However,
these readings still look to be above any record lows.

Rua

MARINE...
A surface low is expected to form along a stalled frontal boundary
off the Lower Texas coast later tonight and move toward the
coastal waters on Monday. The gradient will tighten as the low
strengthens, and therefore winds will also increase and small
craft advisory conditions look to occur for the two southwest
outer zones into Monday Morning. The surface low will also bring a
round of increasing showers and thunderstorms, and some of these
storms by Monday Afternoon will be on the strong side.

As the low moves off to the east on Monday Evening, strong west
winds will then occur over the coastal waters on Monday Night into
Tuesday Morning.

Later in the week, a strong cold front will move into the coastal
waters on early Thursday. Strong and gusty offshore winds are
expected behind this front.

Rua

&&

.PRELIMINARY POINT TEMPS/POPS...
AEX  49  57  48  63 /  90  90  40  10
LCH  53  65  51  68 /  90  90  20   0
LFT  55  69  53  69 /  90  90  40   0
BPT  53  63  50  70 /  90  90  10   0

&&

.LCH WATCHES/WARNINGS/ADVISORIES...
LA...Flash Flood Watch through Monday afternoon for LAZ027>033-
     041>045-052-053-073-074.

TX...Flash Flood Watch through Monday afternoon for TXZ180-201-215-
     216-259>262.

GM...SMALL CRAFT EXERCISE CAUTION through Monday morning for GMZ450-
     452-455-475.

     Small Craft Advisory until noon CST Monday for GMZ470-472.

&&

$$


AVIATION...04


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