Area Forecast Discussion
Issued by NWS Shreveport, LA

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FXUS64 KSHV 181155
AFDSHV

Area Forecast Discussion
National Weather Service Shreveport LA
555 AM CST Sun Nov 18 2018

.AVIATION...
For the 18/12z TAFs, a cold front was located from Palestine TX,
to near Sulphur Springs TX, to near Broken Bow OK, and north-
northeast into Western Arkansas. Ahead of the front, showers will
continue to develop for the first several hours of the period.
KTXK, KTYR, KGGG, and KSHV will be the primary TAF sites to be
impacted. Coverage of the showers will likely decrease after
18/18z as drier air aloft begins to move into the region. Most of
the rain will dissipate or exit the area by 19/00z, but additional
showers will develop and move northward across Louisiana and East
Texas during the last few hours of the period.

As the front progresses eastward, ceilings will fall into the MVFR
range with little change expected after that time in most
locations, but a few instances of IFR ceilings cannot be ruled out
overnight. Surface winds will shift to the west and northwest
following the frontal passage and increase in speed. Wind speeds
may be as high as 10 or 12 kts across portions of East Texas, but
speeds should decrease at all terminals after sunset.

CN

&&

.PREV DISCUSSION... /issued 409 AM CST Sun Nov 18 2018/

SHORT TERM.../Today through Monday/

At 0930z this Sunday morning, a cold front was just entering
McCurtain and Red River Counties. The front is expected to be
near a line from Prescott AR to Lower Toledo Bend Reservoir by
noon today and should finally exit the forecast area after
midnight tonight. Latest radar loops show a line of showers has
been developing while rapidly moving east from near Mineola TX
north-northeast into Western Arkansas. Showers will continue to
develop along the frontal boundary through noon and move eastward.
During the afternoon hours, dry air advection behind the front in
the mid and upper levels will likely lead to a decrease in the
coverage of showers across most of the area. Rain will likely
become limited to Deep East Texas where moisture levels are
highest and Southern Arkansas where vertical ascent from an
approaching positively-tilted upper trough will be greatest.

A large temperature gradient can be expected today for daytime
highs. Deep East Texas and North Central Louisiana should warm
well into the 60s before the cold front arrives. Temperatures will
likely fall during the afternoon hours across the remainder of the
area. Locations in Southeast Oklahoma will struggle to get out of
the 40s today due to the cold air advection and thick low cloud
cover. Despite persistent low clouds areawide, a chilly night is
likely across the northwest half of the forecast area. Low
temperatures may approach the freezing mark in the the terrain of
McCurtain County.

The 850-700mb frontal boundary will be far displaced to the
northwest of the surface front. As the upper trough axis slowly
moves southeast across the area, showers will once again increase
in coverage from south to north during the day Monday along the
elevated frontal boundary. Rain chances will generally be
confined to areas along and south of a line from Tyler TX to El
Dorado AR.

Rainfall amounts are expected to remain light, even though
persistent rain chances are expected for most of the short-term
period. Rain totals will likely rain below one half inch.

CN

LONG TERM.../Monday Night through Saturday/
The base of the shortwave trough extending from W and Cntrl TX into
the Lower MS Valley Monday afternoon will quickly shift SE to
near the SE TX/Srn LA coast by daybreak Tuesday, with much drier air
expected to quickly spill SE with the trough passage. However, sct
SHRA should still be ongoing Monday evening over the SE sections of
Ncntrl LA near the cold front, before quickly shifting SE out of the
area by 06Z Tuesday. Thus, have maintained chance pops for this area
Monday evening, before dropping mention after 06Z. A dry NW flow aloft
will yield a picture perfect day areawide Tuesday, although below normal
temps will continue/Monday Night through Saturday/
The base of the shortwave trough extending from W and Cntrl TX into
the Lower MS Valley Monday afternoon will quickly shift SE to
near the SE TX/Srn LA coast by daybreak Tuesday, with much drier air
expected to quickly spill SE with the trough passage. However, sct
SHRA should still be ongoing Monday evening over the SE sections of
Ncntrl LA near the cold front, before quickly shifting SE out of the
area by 06Z Tuesday. Thus, have maintained chance pops for this area
Monday evening, before dropping mention after 06Z. A dry NW flow aloft
will yield a picture perfect day areawide Tuesday, although below normal
temps will continue despite ample insolation.

Our focus remains on the next shortwave that will traverse the Desert SW
Tuesday night/Wednesday morning, and quickly translate E into the
Srn Plains during the afternoon. The GFS and Canadian have trended
much drier with this system Wednesday afternoon and evening, with
virtually no H850 moisture return ahead of the approaching trough, and
dynamic forcing having to saturate the dry column from the top down.
Meanwhile, the ECMWF has trended somewhat closer to earlier runs although
a bit slower with sct SHRA affecting primarily Lower E TX and the Srn
sections of Ncntrl LA Wednesday evening and night. Have slowed down the
timing of the re-introduction of pops Wednesday afternoon, going with
slight chance pops for the WSW sections of E TX, before increasing pops
to low and mid chance for E TX/Wrn LA after 00Z Thursday. However,
drier air should entrain with the shortwave passage thus quickly tapering
the SHRA from W to E Wednesday night.

Cool and dry conditions should return for Thanksgiving Day, but this is
where the medium range progs diverge as the GFS is most aggressive with
the next progressive shortwave passage from the Cntrl and Srn Plains into
the MS Valley Friday. Meanwhile, the ECMWF/Canadian have trended a bit
slower, with convection increasing for the afternoon. Have added low chance
pops areawide Friday afternoon/evening, before drier air quickly entrains E
into the region in wake of the trough passage. The progressive pattern
looks to continue through next weekend as the next trough/closed low
begins to amplify over the Srn Rockies by the latter half of the weekend,
thus returning at least isolated to sct convection to the region just
beyond the end of the extended period. Deepening Srly low level flow
should also result in the return to more seasonal temps by next weekend
as well.

15 despite ample insolation.

Our focus remains on the next shortwave that will traverse the Desert SW
Tuesday night/Wednesday morning, and quickly translate E into the
Srn Plains during the afternoon. The GFS and Canadian have trended
much drier with this system Wednesday afternoon and evening, with
virtually no H850 moisture return ahead of the approaching trough, and
dynamic forcing having to saturate the dry column from the top down.
Meanwhile, the ECMWF has trended somewhat closer to earlier runs although
a bit slower with sct SHRA affecting primarily Lower E TX and the Srn
sections of Ncntrl LA Wednesday evening and night. Have slowed down the
timing of the re-introduction of pops Wednesday afternoon, going with
slight chance pops for the WSW sections of E TX, before increasing pops
to low and mid chance for E TX/Wrn LA after 00Z Thursday. However,
drier air should entrain with the shortwave passage thus quickly tapering
the SHRA from W to E Wednesday night.

Cool and dry conditions should return for Thanksgiving Day, but this is
where the medium range progs diverge as the GFS is most aggressive with
the next progressive shortwave passage from the Cntrl and Srn Plains into
the MS Valley Friday. Meanwhile, the ECMWF/Canadian have trended a bit
slower, with convection increasing for the afternoon. Have added low chance
pops areawide Friday afternoon/evening, before drier air quickly entrains E
into the region in wake of the trough passage. The progressive pattern
looks to continue through next weekend as the next trough/closed low
begins to amplify over the Srn Rockies by the latter half of the weekend,
thus returning at least isolated to sct convection to the region just
beyond the end of the extended period. Deepening Srly low level flow
should also result in the return to more seasonal temps by next weekend
as well.

15

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  61  42  54  40 /  30  20  30  10
MLU  66  50  57  42 /  20  20  40  20
DEQ  53  38  55  34 /  40   0   0   0
TXK  57  39  54  37 /  40  10  10   0
ELD  60  44  55  37 /  30  20  20  10
TYR  57  39  54  39 /  40  20  20   0
GGG  57  40  54  39 /  40  20  30  10
LFK  63  44  54  41 /  30  40  40  10

&&

.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...None.
OK...None.
TX...None.
&&

$$

09/15/09


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