Area Forecast Discussion
Issued by NWS Shreveport, LA

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440
FXUS64 KSHV 211431
AFDSHV

Area Forecast Discussion
National Weather Service Shreveport LA
931 AM CDT Sat Apr 21 2018

.UPDATE...
Only minor changes were made to the ongoing forecast. Cloud cover
is not as thick across some locations as previously forecasted and
thus have adjusted the sky grids to reflect ongoing trends.
Tweaked the sfc temp curve to ensure accurate trends and
subsequently tweaked the dewpoint temperatures and relative
humidity values.

Otherwise, scattered showers and thunderstorms have developed
across central OK and north central TX thus along the leading
edge of an upper level disturbance, as advertised by computer
models. As the system continues to shift east throughout the day,
so will the accompanied precip, which is set to impinge on east TX
and southeast OK aoa 18Z /and spreading eastward thereafter/.

&&

.PREV DISCUSSION... /issued 717 AM CDT Sat Apr 21 2018/

AVIATION...
For the 21/12z TAFs, VFR conditions will prevail at most sites
initially, but ceilings will gradually lower into the MVFR range
from west to east. Convection currently ongoing across Central
Oklahoma and North Texas will move into the area after 21/18z. All
TAF sites will be affected before the end of this period. Flight
conditions will deteriorate as the convection arrives. One or two
isolated storms may become severe. A cold front will help to push
the storms eastward, and the storms should end at most of the
East Texas terminals by the end of the period.

/09/

PREV DISCUSSION... /issued 518 AM CDT Sat Apr 21 2018/

DISCUSSION...
The morning satellite imagery reveals that elevated cloud cover
has rapidly begun to develop/spread ENE across the region this
morning, well ahead of the closed low over Cntrl CO, with the
trailing trough S into Srn NM. Weak sfc ridging remains in place
across the region this morning, but this will change by mid to
late morning as winds veer more SErly as a sfc low over NW TX
begins to shift E into Wcntrl TX along a weak inverted sfc trough
that will develop along the Red River. In fact, the low level
moisture return is not too far off,with MVFR cigs over SE TX
rapidly encroaching on Deep E TX attm. The mosaic radar imagery
has been depicting some elevated mid level returns over portions
of extreme NE TX/SE OK, although sfc obs over these areas have not
recorded any cigs aob 12kft. However, the latest sfc obs from PRX
has just recorded -RA, meaning that a few sprinkles are indeed making
it to the ground.

The air mass should continue to saturate today as mean moisture
continues to spread NE and deepen over the area, as the closed low
emerges out over OK. The short term progs have slowed down the Ewd
progression of the convection this morning though, remaining just
W of the CWA through 18Z (for the most part), before the
convection rapidly expands E into E TX/SW AR/extreme NW LA for the
afternoon. Have slowed down the progression of the Pops as well
this morning, but did bump pops up a bit across SE OK/portions of
extreme NE TX as large scale diffluence increases late in the day.
The heavy rain threat still looks on track for tonight across
much of the region, as a warm front begins to lift N into E TX/N
LA to near the AR/LA border by mid to late evening. The
GFS/ECMWF/HRRR are in good agreement this morning with the track
of the sfc low roughly along or just S of the I-20 corridor this
afternoon and evening, with the 06Z NAM in better agreement now,
but MUCape being limited to 500 J/Kg or less across the warm
sector this evening as dynamical forcing increases this evening
ahead of an increasingly negatively tilted trough axis. Still
can`t rule out isolated strong to severe convection this evening
through a portion of the overnight hours near and S of the warm
front given the limited instability accompanied by 40-50kts of
bulk shear, but believe the primary threat will be for locally
heavy rainfall as the convection deepens within the LFQ of the
120kt upper jet streak, and gradually spreads E across the area.
The high res progs suggest widespread 1-2+ inches of QPF across
much of E TX/SE OK/SW AR/NW LA, with isolated higher amounts of 3+
inches possible given the potential cell training this evening,
before dry slotting aloft begins to entrain E beneath the upper
low after 06Z Sunday. Minor flooding can`t be ruled out tonight
where training is observed, but given the localized instance of
this, will forego a Flash Flood Watch attm.

The attendant cold front will gradually progress SE across the
region late tonight through Sunday morning, exiting the area
by/after 18Z. Did maintain high chance to likely pops Sunday
morning across the Ern zones before this diminishes quickly by
mid-morning, although the potential for some wrap-around -SHRA
will linger across mainly SW AR and Ncntrl LA as the closed low
drifts SE across Cntrl and Srn AR. The biggest question though
remains the max temps, as the post-frontal cloud cover over Deep E
TX/N LA may diminish by afternoon, allowing for better insolation
before the wrap-around stratocu field spreads SE along the
backside of the low. Have trended max temps a tad higher than the
previous forecast, before the deeper wedge of cold air is able to
sink SE.

The post-frontal stratocu should help keep temps a bit cooler
Monday, with isolated -SHRA possible, before the clouds gradually
diminish from W to E with the departure of the closed low. A
warming trend will commence Tuesday, although the next cold front
remains progged to sweep SE through the area Wednesday. There
still remains quite a bit of uncertainty in regards to timing,
with the ECMWF the slower solution by about 12 hrs behind the
faster and more progressive GFS. However, convection should
quickly develop ahead of the associated shortwave trough over the
Cntrl Plains and Mid-MS Valley. Did bump pops up to high chance
Wednesday N of the I-20 corridor, but kept slight chance pops
going Wednesday evening for the Srn 3/4ers of the area given the
potential for lingering convection as drier air deepens in wake of
this shortwave trough/cold fropa.

The progressive pattern looks to continue through the end of the
extended, with another deeper upper trough sliding SE into the Srn
Plains/Lower MS Valley Friday, resulting in additional convection
and a reinforcement of cooler and drier air for next weekend.

Prelims to follow below...

15

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  72  58  71  53 /  50 100  30  10
MLU  75  60  73  55 /  20 100  60  10
DEQ  68  52  67  50 /  80 100  30  10
TXK  70  56  67  53 /  70 100  30  10
ELD  73  58  69  54 /  30 100  50  10
TYR  67  54  66  51 /  70 100  10   0
GGG  69  57  67  51 /  60 100  10   0
LFK  73  59  73  51 /  40 100  10   0

&&

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

$$

29/09/15



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