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fxus64 klch 120000 
afdlch

Area forecast discussion
National Weather Service Lake Charles la
600 PM CST Mon Nov 11 2019

Aviation...
cold front currently moving through southeast Texas just northwest
of Beaumont Texas at this time and extends up into Vernon Parish.
Frontal system is moving to the east southeast. Winds ahead of the
strong cold front are from the south generally less than 10 knots
while behind the front winds become northwest to north at 20 to 25
knots W/ higher gusts. Ceilings are also dropping from VFR ahead
of the front to IFR behind the front and to LIFR deeper into the
front. Visibility to vary from 5sm to p6sm thru the overnight hours.
The issue of the eve and ovrnght hrs will be low ceilings and
very strong gusty winds.

The front is expected through aex and lch by 02z and thru lft and
Ara by 04z.

&&

Previous discussion... /issued 347 PM CST Mon Nov 11 2019/

Synopsis...
a significant early Arctic cold front is expected to move across
tonight with high rain chances just along and behind the front.
Blustery north winds behind the front will provide a dramatic
change in temperatures with conditions more like The Heart of
winter than fall and probably some of the coldest air since
January 2018.

Bullet points...

Near record breaking low temperatures expected for Tuesday night and
Wednesday morning. There is a likelihood of an area wide freeze with
a hard freeze down to the I-10 corridor. Precautions for plants,
pets, pipes, and people should be taken. Hard freeze and freeze
watches have been issued.

Estimated duration below freezing Tuesday night/Wednesday morning...
central Louisiana...around 12 hours.
Lakes and Piney Woods southeast Texas...10 to 12 hours.
Along the I-10 corridor...6 to 10 hours.
South of I-10 corridor to the coast...3 to 6 hours.

Blustery north winds will make for a raw day on Tuesday with wind
chills in the 20s in the morning and 30s in the afternoon. This will
be a dramatic change from apparent temperatures in the upper 70s
today. The north winds may also cause some travel problems for
high profile vehicles and blow around unsecured lawn objects. A
Wind Advisory has been issued.

Strong and gusty north winds will create hazardous marine
conditions with winds offshore gusting at times between 45 and 50
knots late tonight and on Tuesday. A Gale Warning will be in
effect.

It is unlikely any frozen type precipitation falls in the
forecast area. Even if a brief period of sleet mixing in with the
rain can occur in the far northern zones late overnight and very
early Tuesday morning, the impacts will not be significant.

Rua

Discussion...
mild temperatures occurring across the forecast area this
afternoon with readings mainly in the mid to upper 70s. However,
these temperatures are just teasing as to what is expected to be
on the way as dramatic changes will occur tonight into Tuesday.

The culprit for the dramatic airmass change is a sharp northern
stream upper level trough that is amplifying as it moves east of
The Rockies and across the plains. This will allow a 1043 hpa
surface high with polar origins to build southward and push an
Arctic intrusion down to the Gulf Coast.

The Arctic cold front is making good progress through Texas and as
of of 11/21z has moved through the San Antonio to Texarkana areas.
Good agreement with the front moving into the forecast area right
before sunset for northwest areas, then through the remainder of
the forecast area during the evening hours, before being off the
coast by midnight.

Moisture profiles have been increasing as mid and upper level southwest
winds are bringing east pac moisture at those levels and low level
southerly flow is bringing in Gulf moisture. Precipitable water
according to latest laps analysis are ranging from 1.5 to 1.75
inches.

As is typical with these types of fronts, best frontal
convergence and lift is right along and behind the front, and this
is when the interaction with the good moisture with allow widespread
rain showers to develop with the shield of rain showers marching south
during the evening and overnight as the front quickly moves
through. Instability looks rather weak so will keep activity as
showers and not mention any thunder. With the high moisture values
could be some moderate rainfall with the activity.

The question as to any wintry mix. At this time, consensus of
forecast soundings, top-down procedure, and other local winter
weather procedures, show that when favorable thermal parameters
develop, and surface temperatures drop to near freezing, moisture
is lacking. As the Arctic airmass is shallow, even the worse case
or best case (depending on how you look at it) for any wintry
precipitation have about a 7-9 thousand foot warm layer above 95h
with temperatures in the layer around 5c. Then a small layer of
sub-freezing above the surface, before temperatures at the surface
again go above freezing.

Therefore, there is an outside chance that a few sleet pellets
may mix in before the moisture ends across the very extreme
northern zones for one or two hours after 3 am til around
sunrise. However, with surface temperatures remaining above
freezing and drying quickly after sunrise, anything would be
insignificant and will not mention any frozen precipitation in the
zones or grids.

A big drop in temperatures will occur, as afternoon temperatures
on Tuesday will be some 30f to 35f degrees lower than from Monday
afternoon, as temperatures struggle to get into the 40s. It will
also be a raw day, as blustery north winds will help keep wind
chills in the 20s during the morning and 30s in the afternoon.

Wind speeds behind the front will be around 20 mph with gusts to
around 30 mph or higher into Tuesday afternoon, so will have a
Wind Advisory going to cover this.

Clearing skies and winds becoming light as the strong high pressure
settles in on Tuesday night and Wednesday morning look to make for
very cold conditions and more like a January cold blast than one
in November, and quite likely this will be the coldest airmass
since January 2018.

Guidance operational MOS numbers are still coming into better
agreement, with European model (ecmwf)-ecm, GFS-mav, NAM-met operational numbers
all within one to three degrees of each other, and also very close
to the mean and 50 percentile ensemble member numbers. Even the
90 percentile ensemble numbers, or in theory how cold it should
at-least get show a freeze area wide with a hard freeze for the
northern zones.

Therefore, will go with a blend of the operational guidance and
this gives near record or record breaking cold temperatures for
the lows on Tuesday night/Wednesday morning, and an area wide
freeze will occur, with a potential hard freeze down to the I-10
corridor. Upgrades to hard freeze warnings and freeze warnings
will come later once we pin down the fine details with local hard
freeze criteria temperatures 25f degrees and below.

Warming trend will start during the day on Wednesday and into
Wednesday night as the high begins to weaken and move off to the
east.

Still some differences going into Thursday with a southern stream
short wave moving across and how much return flow moisture it can
work with. GFS is on the dry side with best moisture mainly for
along the coast and offshore and European model (ecmwf) is a little more wet, with
moisture for the entire forecast area. The good news is that the
rainfall amounts would be light if it occurs or not. At this
point will keep close to the National blend and super blend
numbers for the late Wednesday night into Thursday period.

Temperatures overall during the period look to be below climo
norms into the weekend.

Rua

Marine...
an Arctic cold front will enter the coastal waters before midnight
and sweep through the coastal waters before daybreak. A 1043 hpa
surface high building in behind the front will allow for a tight
pressure gradient across the northwest Gulf of Mexico. Also, strong
cold air advection will be noted behind the front bringing cold
air over relatively warmer Gulf waters. This will allow rather
turbulent conditions and mixing bringing strong and gusty north
winds down to the surface. As the winds increase, seas will also
build becoming quite rough.

Sustained winds tonight into Tuesday afternoon are expected to be
30 to 35 knots with gusts over 45 knots over the coastal waters
with seas building to 7 to 11 feet beyond 20 nm and 3 to 7 feet
within 20 nm. Therefore, a Gale Warning has been issued.

For the coastal lakes and bays winds will be 20 to 25 mph with
higher gusts, so a Small Craft Advisory has been issued for those
areas.

Usually we would see quite a drop in waters levels, especially out
of the lakes and bays, as the offshore winds push water away from
the coast. Guidance does show tide levels will be about 1 to 1.5
feet MLLW below astronomical levels during low tide Tuesday
morning. However, with current anomalies being between 0.5 and 1
foot above, this will help mitigate some of the water drop, and
probabilistic tide guidance has lowest water levels around (-0.7)
feet MLLW, which does not quite reach The Levels for a low water
advisory, and thus will hold off on issuing one for now.

Winds will decrease by Wednesday as the high pressure settles in and
weakens over the region.

Rua

Climate...
.Perspective on upcoming forecasted cold snap compared to
records...

Wed 11/13 Nov all time last time 25f or below
fcst daily record low
low record

Aex 21f 27f/1911 20f 11/30/1911 25f 3/5/2019*

Bpt 27f 28f/1911 22f 11/30/1976 23f 1/18/2018

Lch 26f 26f/1911 20f 11/30/1911 20f 1/18/2018

Lft 25f 27f/1911 21f 11/16/1916 17f 1/18/2018

Ara 26f 32f/1950 23f 11/30/1976 19f 1/18/2018

*aex low on 1/18/2018 was 14f.

&&

Preliminary point temps/pops...
aex 33 43 21 52 / 90 10 0 0
lch 37 44 26 52 / 80 20 0 0
lft 36 43 25 52 / 80 30 0 0
bpt 37 45 27 51 / 80 20 0 0

&&

Lch watches/warnings/advisories...
la...freeze watch from Tuesday evening through Wednesday morning for
laz052>055-073-074.

Wind Advisory from midnight tonight to 3 PM CST Tuesday for
laz029-032-033-041>045-052>055-073-074.

Hard freeze watch from Tuesday evening through Wednesday morning
for laz027>033-041>045.

Wind Advisory from midnight tonight to noon CST Tuesday for
laz027-028-030-031.

Texas...freeze watch from Tuesday evening through Wednesday morning for
txz215.

Hard freeze watch from Tuesday evening through Wednesday morning
for txz180-201-216-259>262.

Wind Advisory from 9 PM this evening to noon CST Tuesday for
txz180-201-259>262.

Wind Advisory from 9 PM this evening to 3 PM CST Tuesday for
txz215-216.

GM...Small Craft Advisory from 6 PM Tuesday to midnight CST Tuesday
night for gmz450-452-455-470-472-475.

Gale Warning from midnight tonight to 6 PM CST Tuesday for
gmz455-475.

Gale Warning from 9 PM this evening to 6 PM CST Tuesday for
gmz450-452-470-472.

Small Craft Advisory from 9 PM this evening to 3 PM CST Tuesday
for gmz430-432.

Small Craft Advisory from midnight tonight to 6 PM CST Tuesday
for gmz435.

&&

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