681 
FXUS64 KLCH 221149
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
549 AM CST Fri Feb 22 2019

.DISCUSSION...
22/12/Z TAF Issuance.

&&

.AVIATION...
Widespread LIFR conditions are seen acrs the area this morning,
with a frontal boundary located between ARA and LFT, and extending
SW off the coast south of Cameron. The front is expected to lift
north this morning, with winds at the LFT/LCH/BPT turning 
southeasterly through 16-17Z. As this happens, expect vsbys
improving to VFR and cigs improving to MVFR. At AEX, the front is
expected to move through around midday, followed by improving
conditions. Southerly winds are then expected to prevail through
the remainder of the TAF period, with intermittent -SHRA. Can not
totally rule out TSRA, but point probabilities are too low to 
carry at this time. Cigs are again expected to lower to LIFR this
evening, with patchy fog at the southern terminals reducing vsbys
to MVFR/IFR.

24

&&

.PREV DISCUSSION... /issued 517 AM CST Fri Feb 22 2019/ 

SYNOPSIS...
A potent storm system gathering strength over the southern Rockies
will move eastward through the weekend and provide a roller-
coaster of conditions for the forecast area. First, cooler 
conditions will be replaced by unseasonably warm and spring like
today into the first part of Saturday, then back to more
seasonable winter conditions later Saturday into the remainder of
the weekend. This system will bring some potential hazards to the
forecast area. Dense sea fog will be possible up to the I-10 
corridor this morning, with the dense sea fog lingering near the 
coast into Saturday morning. Also, a Marginal to Slight Risk of 
Severe Weather will be possible, especially ahead of a cold front
that the storm system will bring on Saturday.

Rua 

DISCUSSION...
A warm front as of 22/10Z was located from around New Iberia
Louisiana (KARA) to about 40 miles south of High Island Texas.
This front has been quasi-stationary overnight, however looks to
be moving to the northwest again as winds have just become
southerly again at KARA and temperatures and dew points are up to
the upper 60s. Typical pre-warm frontal conditions are occurring
with lowering stratus developing into areas of fog. This fog may
be dense at times, especially near the coast. 

As strong upper level energy moves east across the southern 
Rockies a storm system and surface low will develop today. This 
will allow southerly flow to increase and accelerate the warm 
front to the north this afternoon. Any fog over inland areas is
expected to lift as the front moves through and wind speeds
increase. Most of the shower activity today will be ahead of the
warm frontal system. Some of the shower activity may become on the
strong side late this afternoon across northern sections of the
forecast area as favorable right entrance region of 50H speed max
intersects the leading edge of the warm frontal boundary. Most
unstable CAPES will be near 1500 j/kg with daytime heating, and
this could lead to elevated convection over the warm frontal
boundary combining with the shear aloft to produce some small to
marginal severe hail. The Storm Prediction Center has outlined the
area north of a line from roughly Woodville to Marksville as
having a Marginal Risk (5 percent) of severe storms. If any strong
storms develop they will diminish in the evening hours with loss
of daytime heating and speed max moving off to the northeast. 

As the upper level storm system moves east out of the Rockies it
will deepen and phase with the strong sub-tropical jet stream and
take on a negative tilt. As this system moves further east it will
trail a Pacific cold front across the forecast area on Saturday
afternoon.

Low level jet will increase ahead of this cold front, and 
southerly winds around 40 knots will be found at 92H. This will 
help further increase the elevated moisture values across the 
forecast area with precipitable water values between 1.75 and 1.90
inches during Saturday, with these values well over twice the
standard deviation and around the moving mean max for this time 
of year. Moisture convergence ahead of the front, and favorable
divergence aloft from the increasing negative tilt of the upper
level trough, will allow widespread shower activity to form, that
will eventually form a squall line along the front.

Meanwhile, increasing southwest winds aloft will be noted with the
upper level system with 50H winds around 70 knots. This will allow
for good shear to develop across the forecast area with 0-6km bulk
values between 50 and 60 knots. With front timing in the afternoon
hours, daytime heating will help increase low level instability.
Most unstable CAPES will be between 1000 and 1500 j/kg, with most
surface based CAPES around 1000 j/kg, which would tend to mean
that some instability will be elevated due to the modified Gulf
marine layer, and how much that modifies or mixes out will play a
big part in how strong or severe the storms will become.

With the respectable wind dynamics and shear values, the Storm
Prediction Center has outlined the forecast area north of roughly
a Beaumont to Lake Charles to Lafayette line in a Slight Risk (15
percent) for severe storms and a Marginal Risk (5 percent) for 
the remainder of the forecast area. Damaging straight line winds
and hail will be the main hazards. However, a few short lived
tornadoes can not be ruled out, especially if storms can become
discrete and/or surface based, as 0-1km helicity values are over
200. 

Cooler and drier air will move in behind the front, ending shower
activity, and setting up a nice Sunday with seasonal temperatures
and sunny skies. 

Still some differences in the guidance as to how much return flow
moisture will move back into the forecast area early next week
before the next significant cold front moves through on Thursday.
Will keep close to the superblend numbers which keeps rain chances
for Tuesday into Thursday.

Rua 

MARINE...
A warm front this morning as of 22/10Z is located across the
coastal waters from just inland of south central Louisiana to
about 40 miles south of High Island Texas. Typical pre-warm
frontal conditions occurring with lowering stratus causing dense 
fog ahead of the front, then south winds bringing warm and moist
air over the cooler shelf waters producing dense sea fog behind
the warm front. 

This warm front is expected to move north and inland during the
morning hours, leaving a light to modest southerly flow over the
coastal waters. This again will continue the problems of sea fog
especially over the near shore waters. The southerly winds will
increase later tonight, as a surface low pressure system develops
east of the southern Rockies. Wind speeds may get to small craft
exercise caution criteria for the outer waters by late tonight
into Saturday morning. The winds may help lift the sea fog some,
although the potential for dense sea fog will likely linger for
the near shore waters into Saturday morning. 

A cold front will move through the coastal waters on Saturday
afternoon. Modest northwest winds will develop behind the front
with the possibility of small craft exercise caution conditions
late Saturday night into Sunday morning. The northwest flow will
bring in drier and cooler air to end sea fog and rain chances for
the remainder of the weekend.

Rua

&&

.PRELIMINARY POINT TEMPS/POPS...
AEX  75  65  75  44 /  60  50  80   0 
LCH  78  68  77  48 /  30  30  70   0 
LFT  79  69  79  51 /  30  20  70  10 
BPT  75  67  75  48 /  50  30  70   0 

&&

.LCH WATCHES/WARNINGS/ADVISORIES...
LA...Dense Fog Advisory until 10 AM CST this morning for LAZ041>045-
     052>055-073-074.

TX...Dense Fog Advisory until 10 AM CST this morning for TXZ215-216.

GM...Dense Fog Advisory until noon CST today for GMZ430-432-435-450-
     452-455.

&&

$$


AVIATION...24