Special Weather Statement, NWS Shreveport, LA

Area Forecast Discussion
National Weather Service Shreveport LA
447 AM CDT Tue May 11 2021

.AVIATION...

Changed very little in the 12z TAF package compared to the 06z TAF
package. Depending on location of convection, either began
prevailing TSRA trending VCTS by mid to late morning, then
prevailing TSRA once again through the end of the TAF package or
began current package with VCTS and trended towards prevailing
TSRA given that overwhelming majority of high res solutions
suggest best storm coverage will be this afternoon into the
evening hours before we lose the coverage across our northwest
airspace later tonight.

Look for ceilings mostly IFR or LIFR with in and out MVFR
conditions as well. Went with VRB on the winds given the multitude
of outflow boundaries that will be present today with mostly MVFR
to IFR VSBYS.

13

&&

.PREV DISCUSSION... /issued 305 AM CDT Tue May 11 2021/

SHORT TERM.../Today through Wednesday/

Getting more and more concerned for the possibility of widespread
flooding issues developing today through tonight as opposed to
more isolated flooding and it is for that reason that a Flash
Flood Watch has been issued with this forecast package to include
all but our extreme northern zones through 12z Wed.

The scenario is really the same as it has been the last 24 hours
or so and that is the heaviest rainfall is not co-located with the
true surface cold front which was located just south of our CWA as
of 07z but more co-located along strong low level theta-e advection
with the head of this low level forcing noted across NE TX just
north of the I-20 Corridor attm. While PWATS at or near 1.5
inches does not scream widespread flash flooding, most of this is
located in the lowest 10kft or so of the profile. When you
combine these factors along with the possibility of the stalled
boundary to our south beginning to slowly lift northward over the
next 12 to 18 hours, not to mention more in the way of upper
forcing upstream coming at us from the Texas Hill Country, then
you have the perfect ingredients for more in the way of widespread
flooding concerns, especially across portions of our CWA which
are very waterlogged from heavier rainfall that has been observed
over the last couple days. Pushed the Flash Flood Watch out
through 12z Wed as at least the northwest portion of our Flash
Flood Watch area should be losing the effects of both low level
and upper level forcing by that time. The watch across our
southern and eastern zones may have to be extended beyond 12z Wed
as this area will likely not be done yet with the heavier rainfall
potential.

Cannot rule out the possibility of some strong to severe
thunderstorms today through tonight as well given the rather steep
lapse rates in place and MUCAPE values but given the increasingly
widespread nature of the convection, this large hail/damaging
wind threat should be isolated, hence the Marginal Risk per SPC's
Day One Outlook.

Upper flow to become more zonal for Wednesday but as stated
above, more in the way of low level forcing may result in the
current Flash Flood Watch possibly needing to be extended for our
southeast but will adjust if necessary attm.

Thanks for the coordination efforts this morning FWD,HGX,LZK,JAN,LIX
and WPC.

Prelims to follow...13.

LONG TERM.../Wednesday Night through Monday Night/

Shower and thunderstorm chances will finally be exiting the region
at the start of this long-term period, as proper upper level forcing
kicks the stalled frontal boundary out of the area. In the wake of
this front, upper level ridging will settles in. This will allow for
a short dry period for the Four-States region under limited forcing,
and dry NW flow. Temperatures during this timeframe will also begin
to rebound to a seasonal feel with limited cloud cover, and the slow
transition to south winds by the weekend.

Things start to get interesting towards the start of next workweek.
At this time, there is pretty good agreement in guidance that
ridging aloft will slightly break down into more SW flow, and a
series of shortwave disturbances begin to move east across Texas.
Due to the increasing dewpoints, these shortwaves will once again
increase shower and thunderstorm chances, particularly in our
western zones on Sunday. By Monday night however, it appears as if a
rather progressive trough will be moving through the plains, along
with a cold front. This cold front will become rather elongated, and
potentially stall SW to NE along portions of Oklahoma and Texas.
While this stalled front will not be stationary nearly as long as
the previous one, it will stall long enough to allow for another wet
48 hours for the area. Both the Euro and GFS favor a band of
potentially heavy rainfall moving across the region towards the end
of this long-term, and into the start of next workweek.

/44/

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  66  56  67  52 / 100 100  40  20
MLU  67  58  68  53 / 100 100  50  20
DEQ  61  49  68  49 / 100  70  30  10
TXK  61  52  67  52 / 100  80  30  10
ELD  61  52  68  49 / 100 100  30  10
TYR  65  54  67  53 / 100  90  40  10
GGG  66  54  66  51 / 100 100  40  10
LFK  76  62  68  55 / 100 100  70  20

&&

.SHV WATCHES/WARNINGS/ADVISORIES...
AR...Flash Flood Watch through Wednesday morning for ARZ070>073.

LA...Flash Flood Watch through Wednesday morning for LAZ001>006-
     010>014-017>022.

OK...None.
TX...Flash Flood Watch through Wednesday morning for TXZ096-097-
     108>112-124>126-136>138-149>153-165>167.

&&

13/13/44

Hazardous Weather Outlook
National Weather Service Shreveport LA
314 AM CDT Tue May 11 2021

ARZ050-051-059>061-OKZ077-120815-
Sevier-Howard-Little River-Hempstead-Nevada-McCurtain-
314 AM CDT Tue May 11 2021

This Hazardous Weather Outlook is for portions of southwest
Arkansas and southeast Oklahoma.

.DAY ONE...Today and Tonight...

Periods of moderate to heavy rainfall will once again be possible
today and tonight, which may result is some localized flash
flooding. A few of these storms may be strong to severe as well.
Damaging winds and hail would be the primary threats with this
activity.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday...

Dry conditions settle in by Wednesday afternoon, and will remain
into the weekend. Shower and thunderstorm chances return by Sunday
night, with moderate rain possible again into Monday.

.SPOTTER INFORMATION STATEMENT...

Activation of emergency management personnel...amateur radio
operators...and storm spotters will be needed this afternoon and
evening.

ARZ070>073-LAZ001>006-010>014-017>022-TXZ096-097-108>112-124>126-
136>138-149>153-165>167-120815-
Miller-Lafayette-Columbia-Union-Caddo-Bossier-Webster-Claiborne-
Lincoln-De Soto-Red River-Bienville-Jackson-Ouachita-Sabine-
Natchitoches-Winn-Grant-Caldwell-La Salle-Bowie-Franklin-Titus-
Camp-Morris-Cass-Wood-Upshur-Marion-Smith-Gregg-Harrison-Cherokee-
Rusk-Panola-Nacogdoches-Shelby-Angelina-San Augustine-
314 AM CDT Tue May 11 2021

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

.DAY ONE...Today and Tonight...

Periods of moderate to heavy rainfall will once again be possible
today and tonight, which may result is some localized flash
flooding. A flash flood watch has been issued for these areas, as
soils are already rather saturated from previous rainfall. A few
of these storms may be strong to severe as well. Damaging winds
and hail would be the primary threats with this activity.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday...

Dry conditions settle in by Wednesday afternoon, and will remain
into the weekend. Shower and thunderstorm chances return by Sunday
night, with moderate rain passable again into Monday.

.SPOTTER INFORMATION STATEMENT...

Activation of emergency management personnel...amateur radio
operators...and storm spotters will be needed this afternoon and
evening.

44

Special Weather Statement
National Weather Service Shreveport LA
238 AM CDT Tue May 11 2021

TXZ125-137-138-150-110830-
Upshur TX-Gregg TX-Harrison TX-Rusk TX-
238 AM CDT Tue May 11 2021

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN HARRISON...
NORTHEASTERN RUSK...SOUTHEASTERN UPSHUR AND GREGG COUNTIES UNTIL 330
AM CDT...

At 237 AM CDT, Doppler radar was tracking a strong thunderstorm over
White Oak, moving east at 40 mph.

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

Locations impacted include...
Longview, Marshall, Kilgore, White Oak, Gladewater, Hallsville,
Clarksville City, East Mountain, Liberty City, West Mountain,
Lakeport, Easton, Union Grove, Warren City, Nesbitt, Rolling Meadows,
Darco and Judson.

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.

&&

LAT...LON 3264 9495 3267 9440 3237 9440 3237 9441
      3236 9444 3237 9445 3237 9446 3239 9449
      3236 9449 3235 9450 3237 9495
TIME...MOT...LOC 0737Z 272DEG 36KT 3251 9485

44

Special Weather Statement
National Weather Service Shreveport LA
320 AM CDT Tue May 11 2021

TXZ138-110900-
Harrison TX-
320 AM CDT Tue May 11 2021

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHERN HARRISON COUNTY UNTIL
400 AM CDT...

At 320 AM CDT, Doppler radar was tracking a strong thunderstorm near
Hallsville, or 7 miles west of Marshall, moving east at 35 mph.

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

Locations impacted include...
Marshall, Waskom, Elysian Fields, Scottsville, Jonesville, Nesbitt,
Darco and Leigh.

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.

&&

LAT...LON 3259 9456 3265 9408 3238 9408 3236 9419
      3240 9456
TIME...MOT...LOC 0820Z 269DEG 32KT 3250 9447

44

Special Weather Statement
National Weather Service Shreveport LA
337 AM CDT Tue May 11 2021

ARZ050-051-059-060-110930-
Howard AR-Hempstead AR-Sevier AR-Little River AR-
337 AM CDT Tue May 11 2021

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL LITTLE RIVER...WESTERN
HEMPSTEAD...SOUTHERN SEVIER AND SOUTHEASTERN HOWARD COUNTIES UNTIL
430 AM CDT...

At 337 AM CDT, Doppler radar was tracking a strong thunderstorm near
Winthrop, or 7 miles northeast of Foreman, moving east at 40 mph.

Half inch hail and winds in excess of 30 mph will be possible with
this storm.

Locations impacted include...
Ashdown, Mineral Springs, Foreman, Wilton, Tollette, Winthrop, Ben
Lomond, Saratoga, Oak Grove, Bright Star and Browntown.

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.

&&

LAT...LON 3370 9440 3388 9440 3393 9389 3367 9389
TIME...MOT...LOC 0837Z 269DEG 33KT 3379 9431

44

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