Severe Thunderstorm Warning 168, NWS Shreveport, LA

Area Forecast Discussion
National Weather Service Shreveport LA
312 PM CDT Sat May 20 2017

.DISCUSSION...
The UL low system that has provided portions of the Southern
Plains and Four-State Region with rainfall the last few days, has
pushed northeast onto the Central Plains late this aftn. The best
large scale ascent is noted north of the FA nearest to the UL
disturbance, but locally there are a few mesoscale features that
are helping to generate/maintain isolated showers and
thunderstorms across deep east TX, southwest AR and southern and
central LA. The diminishing precip across southwest AR were
remnants of the line/cluster of storms of earlier this morning,
which has aided in stabilizing the atmosphere /increasing CIN/. As
such, showers may struggle to develop initially, but any
lingering outflow boundaries could generate precip and storms
moving northeast from southern LA /where CIN is much less/ could
be another way in receiving rainfall across central LA. The
activity moving into deep east TX is within a bit more favorable
airmass as the once overcast area has had breaks in cloud cover
/raising temps into the 70s and 80s/, making way for better
insolation and thus increasing daytime destabilization. It is no
wonder that we along with surrounding offices have had to issue
Significant Weather Advisories for the storm activity across deep
east TX and across southern LA /for 30-40 mph wind gusts and
small hail/, given less cloud cover and better instability.
Although the eastern-half of the CWA is a bit more stable, this
might be short-lived especially if breaks in the cloud cover
occurs. Attention needs to be maintained for an approaching cold
front that is slowly nearing southeast OK and east TX, thus
heading towards a slightly unstable airmass. Short term solutions
such as the NAM and the HRRR hints at isolated showers and
thunderstorms developing along portions of the cold front late
this aftn/early this evening which seems reasonable. However deep
layer shear and MUCAPE is not overly impressive across the
aforementioned areas, but MUCAPE /2000-3000 j/kg/ is adequate
across the eastern-half of the CWA, which may prove to become
useful once daytime destabilization takes place/CIN decreases
later this aftn/evening. It is no wonder the Storm Prediction
Center displays a Slight Risk of severe storms noted along and
south and east of a near El Dorado, AR to to Arcadia LA to near
Hemphill, TX line. Damaging wind gusts and large hail will be the
main threats, as unimpressive deep layer shear exists /less than
50 kts/. As such, we will need to maintain situational awareness
for areas both in and out of the risk area because of the
approaching cold front.

The NAM solution seems to have fallen more in line with the GFS
and the ECMWF wrt the timing of the fropa and the evolution of
the precip. As such, should see the cold front slowly progress
southeastward across the CWA tonight, and push south towards
southern LA by tomorrow aftn. Despite a slightly cooler airmass
being advected in by the front, there will still be chances for
showers and thunderstorms tonight into tomorrow shifting to along
and south of the Interstate 20 corridor, nearest to the front. The
spatial extent of precip will expand as we head into early next
week, with the front returning as a warm front on Monday while
concurrently an embedded impulse in the west-southwest flow aloft
moves across the region. The unsettled wx pattern will continue
on Tuesday as the southern periphery of a broad UA Low across the
middle/upper Mississippi Valley moves across the FA. Although the
best UL support will be exiting the region during the day on
Wednesday, it is not uncommon for showers to develop on the
backside of an exiting system, as a cold front ushers in a
slightly cooler airmass aloft, which may be enough to garner a
little bit of large scale ascent. Thereafter, expect drier
conditions commencing late week, with near zonal flow aloft
prevailing.

Daytime temps in the 70s and 80s today and tomorrow, will drop to
the 70s by Monday, with the onset of another round of precip
/with possible moderate-heavy rainfall/. Wednesday night will be
cooler than we have experienced in quite a few weeks /40s and
50s/, as a sfc ridge settles in and brings about light sfc winds,
decreasing rainfall chances and subsequently clearing out of the
cloud cover, giving way to excellent radiational cooling. Temps
will rebound into the 80s by the end of the week with the quick
passage of an UA ridge.

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  65  80  62  75 /  40  30  20  50
MLU  68  81  63  75 /  40  40  20  50
DEQ  55  80  56  79 /  20  10  10  20
TXK  60  79  59  76 /  30  10  10  30
ELD  62  78  58  77 /  40  20  10  30
TYR  62  79  62  76 /  40  20  30  50
GGG  64  79  61  75 /  40  20  30  50
LFK  70  83  66  76 /  40  50  30  60

&&

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

29

Hazardous Weather Outlook
National Weather Service Shreveport LA
1125 AM CDT Sat May 20 2017

ARZ050-051-059>061-070>072-LAZ001>004-010-OKZ077-TXZ096-097-
108>112-124>126-136>138-149>153-165-166-211630-
Sevier-Howard-Little River-Hempstead-Nevada-Miller-Lafayette-
Columbia-Caddo-Bossier-Webster-Claiborne-De Soto-McCurtain-
Red River-Bowie-Franklin-Titus-Camp-Morris-Cass-Wood-Upshur-
Marion-Smith-Gregg-Harrison-Cherokee-Rusk-Panola-Nacogdoches-
Shelby-Angelina-San Augustine-
1125 AM CDT Sat May 20 2017

This Hazardous Weather Outlook is for portions of southwest
Arkansas, northwest Louisiana, southeast Oklahoma, east Texas and
northeast Texas.

.DAY ONE...This Afternoon and Tonight...

Isolated showers and thunderstorms may develop along a cold front
later this afternoon across portions of southeast Oklahoma, east
Texas, deep east Tx, southeast Arkansas and northwest Louisiana.
Brief wind gusts and small hail may accompany this precipitation
activity.

.DAYS TWO THROUGH SEVEN...Sunday through Friday...

Showers and thunderstorms will continue to be in the forecast
through at least Tuesday of the upcoming work week. A strong cold
front will move through the entire Four State Region Tuesday Night
into early Wednesday bringing an end to the wet weather pattern.
Much cooler temperatures will be in the forecast for the middle
and latter half of the work week.

.SPOTTER INFORMATION STATEMENT...

Activation of emergency management personnel...amateur radio
operators...and storm spotters should not be needed.

ARZ073-LAZ005-006-011>014-017>022-TXZ167-211630-
Union-Lincoln-Red River-Bienville-Jackson-Ouachita-Sabine-
Natchitoches-Winn-Grant-Caldwell-La Salle-
1125 AM CDT Sat May 20 2017

This Hazardous Weather Outlook is for portions of south central
Arkansas, north central Louisiana, northwest Louisiana and east
Texas.

.DAY ONE...This Afternoon and Tonight...

Plentiful low level moisture coupled with daytime heating will
result in isolated to scattered showers and thunderstorms across
portions of deep east Texas, central and northern Louisiana later
this afternoon, with the potential for additional precipitation
this evening due to the passage of a cold front. Some of these
storms could approach strong to possibly severe levels with large
hail and gusty winds the primary threats. The activity should
start to wane late tonight/early tomorrow morning.

.DAYS TWO THROUGH SEVEN...Sunday through Friday...

Showers and thunderstorms will continue to be in the forecast
through at least Tuesday of the upcoming work week. A strong cold
front will move through the entire Four State Region Tuesday Night
into early Wednesday bringing an end to the wet weather pattern.
Much cooler temperatures will be in the forecast for the middle
and latter half of the work week.

.SPOTTER INFORMATION STATEMENT...

Activation of emergency management personnel...amateur radio
operators...and storm spotters may be needed later today into
the evening hours due to the possibility of severe thunderstorms.

Special Weather Statement
National Weather Service Shreveport LA
310 PM CDT SAT MAY 20 2017

TXZ165-202045-
Angelina TX-
310 PM CDT SAT MAY 20 2017

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL ANGELINA COUNTY UNTIL 345
PM CDT...

At 310 PM CDT, Doppler radar was tracking a strong thunderstorm over
Diboll, moving northeast at 25 mph.

Half inch hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Lufkin, Diboll, Hudson, Huntington, Burke, Zavalla, Redland, Shawnee
and Homer.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3111 9472 3110 9474 3115 9486 3118 9485
      3121 9487 3122 9486 3123 9486 3126 9490
      3128 9488 3130 9488 3145 9470 3115 9436
      3109 9469
TIME...MOT...LOC 2010Z 236DEG 21KT 3117 9474

09

Special Weather Statement
National Weather Service Shreveport LA
653 PM CDT SAT MAY 20 2017

TXZ165-210100-
Angelina TX-
653 PM CDT SAT MAY 20 2017

...SIGNIFICANT WEATHER ADVISORY FOR WESTERN ANGELINA COUNTY UNTIL 800
PM CDT...

At 653 PM CDT, Doppler radar was tracking a strong thunderstorm
near Diboll, moving northeast at 15 mph.

Half inch hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Lufkin, Diboll, Hudson, Huntington, Burke, Redland, Clawson, Homer
and Central.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3111 9472 3111 9475 3115 9485 3123 9486
      3125 9487 3126 9490 3128 9488 3130 9490
      3133 9490 3134 9491 3134 9495 3135 9496
      3150 9485 3130 9447 3110 9470
TIME...MOT...LOC 2353Z 214DEG 15KT 3115 9480

15

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