Area Forecast Discussion
Issued by NWS Lake Charles, LA

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000
FXUS64 KLCH 180523
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
1123 PM CST Sun Dec 17 2017

.AVIATION...LIFR conditions will prevail for most of tonight into
Monday morning. Showers and some thunderstorms can also be
expected. Ceilings and vis may improve into mid to late morning,
however Widespread rain and thunderstorms will keep IFR conditions
possible through the day. Winds will be generally light and from
the northeast to southeast.

&&

.PREV DISCUSSION... /issued 1000 PM CST Sun Dec 17 2017/

DISCUSSION...
A warm frontal boundary will continue moving slowly northward
tonight across Southeast Texas through Southern Louisiana before
becoming stationary once again Monday. Main issues overnight will
be the lowering ceilings to near ground level causing areas of
dense fog, and marine fog advection across the coastal waters
inland south of the front. Sporadic observations already
reporting dense fog near 1/4sm in Central and Southern Louisiana,
but not everywhere at the present time. The areas of fog will
likely expand overnight per continuing trends and guidance. For
this, issued Dense Fog Advisory for all of SE TX/C and SC LA
through 9 am, and the coastal waters out 20nm through 9 am.

The other issue is increasing convection across the coastal waters
will gradually increase overnight and spread northward, and will
likely improve visibility somewhat in the heavier storms expected
by daybreak through the day Monday. The precipitation chances
remain mostly unchanged.

DML

MARINE...
Marine fog will steadily increase as moisture rich air is
transported atop relatively cooler shelf waters. For this, a Dense
Fog Advisory is issued for the inland lakes/bays and coastal
waters out 20 nautical miles. The probability of marine fog will
continue for all of the coastal waters on Monday, and remain
elevated until a frontal passage late Tuesday night into
Wednesday.

DML

PREV DISCUSSION... /issued 512 PM CST Sun Dec 17 2017/

AVIATION...Ceilings will lower through the evening across the
I-10 corridor terminals. KAEX is north of the warm front currently
with LIFR conditions and this will continue. Rain and fog can be
expected to keep inclement conditions lingering into Monday
morning.

PREV DISCUSSION... /issued 451 PM CST Sun Dec 17 2017/

DISCUSSION...
Upper air analysis/water vapor satellite imagery showed the
shortwave trof that aided the convection overnight and this
morning continuing to race eastward and shear apart N of the Ohio
River. To the southeast, a deep layer ridge is centered over S FL
and the Bahamas. Out west, base of upper trof that dug into the
WRN CONUS yesterday has cut off over NW Mexico. NW Gulf coast
region resides within deep SW flow between this cut off low to the
west and the upper ridge to the SE.

At the SFC, a weak frontal boundary that pushed W-E through the
coastal waters and South Central LA overnight has become rather
diffuse and difficult to locate inland, but appears based on SFC
Obs and satellite imagery to extend from roughly SC/SE LA
southwest into the West Central Gulf. Abundant MSTR and persistent
lift on the "cool" side of this boundary resulted in shower
activity continuing across South Central LA and the adjacent
coastal waters through the morning and into early afternoon, with
the lift finally easing/shifting east by mid to late afternoon.

Small rain chances continue in the forecast this evening over the
SE half or so of the area, with probabilities increasing markedly
after midnight as strengthening isentropic ascent develops atop a
sharpening warm front expected to settle near a line from Morgan
City to 60 nm south of High Island. Guidance is hitting pretty
hard on marine/advection type fog over the coastal waters east of
Sabine Lake with subsequent spreading inland across SC/SW LA. More
uncertainty exists to the NW where developing and lowering CIGS
and/or cooling of the moist boundary layer could also yield fog
formation. Have confined fog mention in the forecast to the
former, but will alert evening crew to the possibility of the
latter.

WMFNT is progged to remain near the coast Monday morning, with
inland convection becoming more widespread. Boundary and
associated convection will lift N thru the afternoon, with the
bulk of the rainfall pulling north of the area by tomorrow
evening. A warm and moist marine airmass will be left in place,
resulting in a narrowing diurnal temperature range along with a
continuing risk of marine fog. Highs tomorrow are expected to
climb into the mid/upper 60s with lows tomorrow night/Tues morning
only fall to the lower/mid 60s.

Rain chances start to increase again on TUE as the upper low out
west opens up and ejects eastward across TX, with a SFC low
progged to develop over E TX by TUE evening and subsequently push
eastward along roughly the I-20 corridor TUE night. A trailing
SFC front/trough will swing through the area TUE night into early
WED, with a punch of drier air bringing rains and the risk of sea
fog to an end.

The reprieve looks to be short lived however as south winds return
THU ahead of a robust WRN CONUS trof, which will bring back higher
moisture and warmer temperatures to end the week. Concerning this
trof and its impact over the weekend and beyond, operational
global models have continued to trend away from a significant cold
air intrusion at least prior to Christmas day, though there
remains considerable spread (20 to 30 degrees F) in their
respective ensemble guidance. Ensemble means offer the most
reasonable solution at this time until this spread narrows and
confidence increases.

13

MARINE...
A nearly stationary frontal boundary is expected to retreat slowly
northward tonight and become stationary again near a Morgan City
to 60 nm south of High Island line by early Monday. South winds
will prevail to the south of the boundary with an east to
northeast flow to the north of it. Increasing lift after midnight
will aid in generating scattered showers and thunderstorms after
midnight along and to the north of the front, with this activity
becoming more numerous as it moves inland in tandem with the
boundary on Monday. The risk of marine fog development will
steadily increase as moisture rich air is transported atop
relatively cooler shelf waters, with the risk tonight highest
mainly east of Sabine Lake. The probability of marine fog will
increase for all of the coastal waters on Monday, and remain
elevated until a frontal passage late Tuesday night into
Wednesday. This front will also be accompanied by scattered
showers and thunderstorms, but will usher a brief shot of drier
air into the coastal waters, before moisture and rain chances
increase again on Friday.

13

&&

.PRELIMINARY POINT TEMPS/POPS...
AEX  54  64  60  73 /  30  60  30  40
LCH  59  68  63  74 /  40  70  20  30
LFT  61  70  65  75 /  50  70  20  20
BPT  58  68  63  74 /  40  70  30  40

&&

.LCH WATCHES/WARNINGS/ADVISORIES...
LA...Dense Fog Advisory until 9 AM CST Monday for LAZ027>033-041>045-
     052>055-073-074.

TX...Dense Fog Advisory until 9 AM CST Monday for TXZ180-201-215-216-
     259>262.

GM...Dense Fog Advisory until 9 AM CST Monday for GMZ430-432-435-450-
     452-455.

&&

$$


AVIATION...05


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