Area Forecast Discussion
Issued by NWS Lake Charles, LA

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FXUS64 KLCH 170344

Area Forecast Discussion
National Weather Service Lake Charles LA
944 PM CST Sat Dec 16 2017

Wx map shows the 1012mb surface low moving northeast along the TX
coast this evening, with widespread 25 kts winds eastward across
the coastal waters, see marine discussion below. Radar showing
large area of light to moderate rainfall entering inland SE TX
over the last hour, with heavy rainfall being noted SE of GLS with
the apex of the sfc low. This area will continue to progress
eastward as the surface low moves over the region overnight. For
the forecast, minor update to QPF, but still expecting 0.50-1.00"
as the system moves through overnight. Otherwise, ongoing forecast
on track.



East winds of 25 kts with gusts over 30 kts will continue this
evening through early Sunday morning over the coastal waters as an
area of low pressure moves up the Texas coast. Winds will peak
from the southeast this evening through early Sunday morning, then
begin to diminish from west to east as the low moves northeast of
the area. For this and the higher seas expected to linger, had to
extend the Small Craft Advisory through 3 am. Also, with the winds
transporting very moist and warmer air atop relatively cool
nearshore shelf waters, kept patchy fog late tonight and possibly
persisting for a few days.



.PREV DISCUSSION... /issued 515 PM CST Sat Dec 16 2017/

AVIATION...MVFR ceilings are beginning to develop over the area
and will continue to lower through the night. Rain will also
spread over the region through the evening hours with lower vis
possible. TSRA will also be possible past midnight.

PREV DISCUSSION... /issued 357 PM CST Sat Dec 16 2017/



Latest upper air analysis/water vapor satellite imagery showed a
shortwave trof over W TX, with a deeper and more robust trof
digging into the WRN CONUS. Downstream of these features, an upper
ridge extended west from the Bahamas into the Gulf of Mexico. SFC
analysis revealed an E-W oriented quasi-stationary frontal
boundary stretching across the Central FL peninsula and then WWD
across the Central Gulf to a weak/broad low NE of Brownsville, TX.

Continued digging and eventual cut-off of the base of WRN CONUS
trof will force a rapid NE ejection and opening of the W TX
shortwave, which will take on an increasingly negative tilt while
accelerating TWD the Mid MS River Valley. At the SFC, the weak SFC
low is progged to lift NEWD into SE TX this evening, with an
attendant N-S oriented inverted trof developing over E TX. It
appears at this time that the stationary front (or warm front by
this point) will be left behind and remain over the Gulf waters,
though it may push near the coast overnight and perhaps just
inland across South Central LA prior to daybreak.

The SFC trof and weak low will then trek more EWD across LA
during the overnight and Sunday morning hours. Already
strengthening kinematic fields will only get stronger this evening
and overnight with the arrival of 60-70KT mid and upper level
speed maxima concurrent with the development of a 50-60KT LLJ.
Significant moistening will result, with PWATs progged to approach
2 inches (or 1 to 2 standard deviations above the norm). This
abundant moisture coupled with strong forcing for ascent will
yield widespread rain with embedded heavier showers and
thunderstorms overspreading the area generally from W to E
beginning this evening and continuing through the overnight hours
into SUN morning. Brief but HVY rain will tend to focus along and
just W of the SFC low and inverted SFC trof, with the highest QPF
axis expected to occur to our W and NW this evening, then push
east through the area after midnight into SUN morning. Due to the
progressive nature of the event, do not anticipate any widespread
or significant flooding concerns, though some localized/nuisance
type flooding in urban or low lying areas is possible.

While the forecast wind fields sound ominous, and indeed result in
large cyclonically curved hodographs appearing on forecast
soundings, the primary limiting factor to severe convection is
also apparent with the presence/maintenance of a SFC/low level
cool stable layer. A result of the warm front remaining to our
south. Thus, thunderstorm activity is expected to remain elevated
for most of the area for the duration of the event, but again with
the boundary forecast to reach near the SE TX/SRN LA coast late
tonight and perhaps push a bit inland into SC LA early SUN
morning, SFC based storms posing a tornado/damaging wind risk
cannot be totally ruled out.

As for temperatures tonight, readings are likely to initially drop
this evening before rising with the influx of higher MSTR,
thickening cloud cover, and onset of PCPN.

Lift is progged to weaken markedly by SUN afternoon as the
shortwave trof pulls away to the NE and some slightly drier air is
forecast to push in from the west. Temperatures are forecast to
warm into the 70s. The reprieve in rain will be short lived as
the aforementioned warm front remains stalled over the area. The
upper ridge to the SE is forecast to amplify while the upstream
cut-off low only slowly meanders EWD. In the presence of the
stalled boundary, subtle impulses ejecting ahead of the low and
rounding the ridge will act upon recovering moisture and
increasing though still marginal instability to produce scattered
to numerous showers and thunderstorms SUN night through MON night.
Best rain chances will shift NWD along with the SFC boundary
early TUE, but the approach of the upper low (now over TX) and the
development and eastward track of another SFC low will promote
widespread showers and thunderstorms TUE afternoon and night, with
rains ending WED as drier air pushes in from the west.

Warm and mostly dry weather will continue through THU, with rain
chances increasing THU night and FRI as a potent CDFNT approaches
and pushes into the area.


An upper trough will approach the area tonight resulting in
widespread showers and thunderstorms. East and then southeast
winds are forecast to increase as an associated weak area of low
pressure develops and tracks northeast along the Texas coast into
the Sabine River Valley. The south winds will aid in transporting
very moist air northward atop relatively cool nearshore shelf
waters, so there is some potential for marine fog starting late
tonight and possibly persisting for a few days. Winds will
decrease late tonight into Sunday. Rain chances will continue to
start the new work week as another upper trof slowly approaches
the area from the west.



AEX  47  68  54  68 /  90  20  40  60
LCH  56  70  59  71 /  90  30  50  70
LFT  56  71  62  72 /  90  80  60  70
BPT  53  69  57  71 /  90  20  50  70


GM...Small Craft Advisory until 3 AM CST Sunday for GMZ450-452-470-

     Small Craft Exercise Caution until 3 AM CST Sunday for GMZ430-



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