Scientific Forecaster Discussion
fxus64 klch 210457
Area forecast discussion
National Weather Service Lake Charles la
1157 PM CDT sun Oct 20 2019
21/06z taf issuance.
some mid/high clouds continue to stream over the northwest Gulf into
southern la. Klch radar is indicating some patchy light to modt
rain in association with these clouds. Lft/Ara are the locations
likeliest to see any -ra as this activity moves over the area
tonight, but nothing has been reported by ASOS sites so far. Made
only minor changes to the rest of the tafs. Kept frontal timing
similar to previous issuance, although somewhat low confidence
with hi-res guidance showing a faster transit through the area
than the NAM/GFS. Rain will taper off with the wind shift, but
some low clouds could linger a few hours before drier air leads to
improving sky conditions during the evening Monday.
Previous discussion... /issued 1002 PM CDT sun Oct 20 2019/
southerly winds has brought in dew points in the mid 70s across
southeast Texas and southern Louisiana and upper 70s down along
the beaches. Temperatures are in the upper 70s. Klch radar is
showing rain patches over the coastal waters moving east
Looking back to the northwest to north several tornados watches are
out for storms moving out of the dfw/ftw Metro-plex ahead of a
strong cold front west Wichita Falls in north central Texas attm.
Severe storms have also been detected in northeast Texas and
northwest Louisiana around the shv lctn. The front will move
southeast overnight with storms ahead of the system moving into
the lakes region in southeast Texas around sunrise spreading into
se TX and SW la. Frontal passage into southern Louisiana looks to
be towards the late afternoon.
Current zones are fine at this time. No updates planned.
Previous discussion... /issued 717 PM CDT sun Oct 20 2019/
21/00z taf issuance.
conditions are initially VFR with some mid/high clouds beginning
to spread over the area from the SW. A few rain showers/thunderstorms and rain will be
possible overnight, mainly at bpt/lch, with southerly winds 5-10
knots expected to prevail. Clouds as well as convection will
increase through Monday morning with MVFR cigs developing ahead
of a cold front that will cross the area during the day (~17-19z
at bpt, ~18-20z at lch/aex, ~19-21z at lft/ara). The front will be
accompanied by a band of thunderstorms and rain with gusty winds, heavy rain and
low MVFR cigs possible. Winds will shift to the northwest behind the
front, with showers and storms tapering off and cigs gradually
Previous discussion... /issued 410 PM CDT sun Oct 20 2019/
showers and thunderstorms will be increasing tonight and continue
through Monday as a cold front moves across the region. Some of
these storms could be strong to severe with gusty straightline
winds, although an isolated tornado can not also be ruled out,
along with locally heavy rainfall.
Minor coastal flooding will be possible along the coast and near
coastal lakes and bays during high tide times this evening into
Cooler conditions with fair weather behind for Tuesday into
Another frontal system to potentially affect the region late in
southerly flow has helped increase moisture across the forecast
area today, and that combined with daytime heating has produce
some shower and thunderstorm activity. This diurnally driven
activity should decrease during the evening hours.
Water vapor imagery shows a strong upper level trough moving out
of The Rockies into the plains. This system will continue to move
off to the east and strengthen over the next couple of days and
help bring a cold front across the forecast area on Monday.
Frontal timing is still not exact with hi-res guidance a little
faster with a stronger convective squall line, during the morning and
the global models a tad slower moving the front in from late
morning into the afternoon. A lot will depend on how strong a
projected squall line along the front is tonight as it moves to
the southeast. Right now the most likely scenario is squall line
will be on the edge of the forecast area near daybreak, then begin
to slow and weaken during the morning hours as it moves to the
southeast, then will exit into the coastal waters around mid
afternoon west to late afternoon east.
Low level jet is expected to develop by morning ahead of this
system, with southern stream mid level speed Max bisecting the
region during the day on Monday. Therefore, shear values should be
favorable. Question is instability as convective available potential energy and lapse rates are
modest, mainly due to activity expected to develop overnight in
the Gulf that could rob some of the instability and inflow into
the front. The Storm Prediction Center has outlined portions of
the forecast area northeast of an Opelousas to Woodville in a
slight risk for severe storms for Monday morning and afternoon,
and a marginal risk for the remainder of the forecast area.
Straightline wind gusts will be the main hazard, although good
0-1km helicity values would suggest that an isolated tornado can
not also be ruled out.
The southerly flow will bring in ample Gulf moisture with
precipitable water values progged to increase to between 1.8 and 2
inches by Monday morning, which will be over the 90th percentile
for Storm Prediction Center climatology for this time of year. Therefore, some locally
heavy rainfall will be possible with the stronger convection. Some
of the hi-res cams have rainfall rates between 1 and 2 inches per
hour, and could produce some isolated street flooding or flooding
in low lying poor drainage areas. The overall progressive nature
at this time will keep the excessive rainfall risk at a marginal
level which is outlined by the weather prediction center for the
entire forecast area on Monday.
Cooler and drier air will be moving in behind the front with skies
clearing out during Monday evening and by Tuesday morning. The
high pressure system behind the front will settle in over the
forecast area on Tuesday night into Wednesday morning with low
temperatures possibly in the upper 40s to lower 50s during that
The high will move off to the east on Thursday with southerly
winds and moisture returning.
There is some differences with the frontal system for the end the
week between the European model (ecmwf) and GFS. At this point will just go with
the blend which has high rain chances from Thursday night into
southerly winds will be increasing tonight as low pressure deepens
over the plains and a cold front approaches the coastal waters.
Wind speeds will be in the 15 to 20 knot range west of
Intracoastal City, so small craft exercise caution will be
headlined for those zones.
The cold front will move across the coastal waters during the
daytime hours exiting in the evening hours. Showers and
thunderstorms are expected ahead and along the front.
Strong north winds are expected behind the front as cold air
advection occurs over the warmer Gulf waters. Winds will be around
20 knots from Monday night into Tuesday and Small Craft Advisory
conditions will be possible during that time frame.
The high pressure system will settle over the region late on
Tuesday and Tuesday night, briefly decreasing wind speeds.
Winds will become easterly on Wednesday and onshore on Thursday as
the high pressure system moves off to the east.
Preliminary point temps/pops...
aex 71 78 49 74 / 20 90 20 0
lch 74 79 55 75 / 20 80 20 0
lft 74 80 56 74 / 10 90 30 0
bpt 75 79 56 76 / 40 90 20 0
la...coastal flood advisory until 11 am CDT Monday for laz041-052>054-
Texas...coastal flood advisory until 11 am CDT Monday for txz215-216.
GM...small craft exercise caution until 11 am CDT Monday for gmz450-