River Flood Warning 33, NWS Fort Worth, TX

Area Forecast Discussion
National Weather Service Fort Worth TX
632 PM CDT Sat Aug 12 2017

.AVIATION...
The first wave of convection has moved through the DFW Metroplex
airports this evening. The stalled frontal zone has been affected
by convective outflow and the convergent axis is now draped almost
immediately along I-20. As a result, winds have turned to the NE
at DFW area airports and will likely remain NE for the next
several hours. A lull in convection in expected to last through
this evening before some redevelopment takes place overnight. This
will be due to an intensification of the low-level jet and warm
advection near the 925mb/850mb frontal zones which remain situated
farther north, closer to the Red River. Have maintained some TS
mentions beginning around midnight for Metroplex TAF sites when
some more widespread showers and storms could cause some
substantial aviation impacts again. There is still quite a bit of
uncertainty in where this activity will be located, and if trends
suggest this activity will remain farther north of the DFW area,
then future TAFs issuances could remove quite a bit of TS from the
current TAFs.

Otherwise, some MVFR stratus is possible Sunday morning in the
wake of convection and in vicinity of the stalled front. Showers
may also be lingering through early Sunday morning but think the
thunder potential will have subsided after about 6AM. Winds should
start to come back around to the SE from the E throughout the day
tomorrow. There is a chance for storms to redevelop with daytime
heating Sunday afternoon, and have included a few hours of VCTS
at Metroplex TAF sites. The location of these storms will be
dependent on any outflow boundaries from overnight/morning
convection so confidence is very low in this potential at this
time.

For Waco, most activity is expected to remain well to the north
throughout the TAF period, although a few showers are possible
early Sunday morning. Will need to consider the chance for
scattered storms to develop near the Waco site on Sunday afternoon
for subsequent TAFs, but the potential is too low to include in
the TAFs at this time. VFR conditions and predominantly south
winds will prevail at Waco through the period.

-Stalley

&&

.SHORT TERM... /Issued 307 PM CDT Sat Aug 12 2017/
Potential severe weather and flash flooding continue to be the
highlights of the forecast through the next 12-18 hours.

Scattered showers and thunderstorms have developed across North
Texas this afternoon in vicinity of a stalled front near HWY 380
with aid from an upstream shortwave. Temperatures have climbed
into the mid and upper 90s south of the front, which when combined
with dewpoints in the low 70s, have yielded strong surface-based
instability of 2000-3000 J/kg. Deep layer shear is also on the
increase as a mid-level speed max associated with the approaching
shortwave becomes positioned along the Red River. The 40 kts of
shear in place will be supportive of supercell storm structures,
and much of the ongoing activity has already displayed weakly
rotating updrafts. These initial storms pose a severe downburst
potential given DCAPE values over 1200 J/kg. If a more robust
supercell can get going immediately along the front, it would also
have the potential for a brief tornado spin-up given the locally
enhanced helicity in vicinity of the boundary. Even though lapse
rates aren't incredibly steep, a rotating storm would also have
the ability to produce some severe hail. Later this evening, some
of these more isolated storms should grow upscale and move across
North Texas in the form of a complex or two. A damaging straight-
line wind threat will exist if this scenario comes to fruition.

Tonight and through the overnight hours, the concern will shift
from severe weather to the flash flooding potential. It appears
as through the front will remain in North Texas overnight rather
than lifting north toward Oklahoma. The front will serve as a
focus for training thunderstorms that will be continuously
generated via ascent from both the strong upstream shortwave in
conjunction with low-level convergence and warm advection at the
nose of an intensifying low-level jet. A Flash Flood Watch remains
in effect for our far northeastern areas, but depending on
trends, we may need to expand it southwestward toward the DFW area
if a southward trend in the front's position continues. Wouldn't
be surprised to see an isolated rainfall total of 5+ inches
somewhere in northeast Texas by Sunday morning. All guidance has
been persistently targeting areas from Gainesville to Paris to
Greenville for the epicenter of heaviest rainfall where the flash
flood potential is the highest tonight. If outflow was to force
the front farther south, then the heavy rain axis would follow.

There is still uncertainty regarding how far south activity may
reach overnight or early Sunday morning. It's possible that
eventually an outflow boundary could move southward into Central
Texas toward the Waco area leading to some scattered showers or
thunderstorms early Sunday morning. Severe weather or flash
flooding is not expected in Central Texas through this time frame
as all activity is expected to be on a downward trend.

-Stalley

&&

.LONG TERM... /Issued 307 PM CDT Sat Aug 12 2017/
/Sunday through Saturday/

Complex of showers and thunderstorms should be ongoing during the
start of Sunday, although the most intense heavy rainfall will
likely have shifted farther to the east into the Arklatex. We'll
maintain some high PoPs across our northeast counties during this
time as strong low level warm advection will continue and we'll
still be dealing with the remnant frontal boundary. As the main
forcing for ascent from the shortwave passes off to the east, we
may see a southward push to the frontal boundary through early
afternoon. There will likely be a period of subsidence in the
wake of morning convection and on the back side of the departing
shortwave trough, which will likely suppress additional convection
into the afternoon hours. By late afternoon, there may be
sufficient convergence along the boundary for isolated to
scattered showers and thunderstorms, mainly from the Metroplex
southward into the Waco area.

By Sunday night, continued strong low level warm advection will
persist and be strongest west of I-35. Despite a lack of any
significant shortwave, scattered showers and perhaps a few
thunderstorms are expected to develop in the warm advection regime
mainly across our western counties into the Red River region. Most
of the precipitation should come to and end during the day on
Monday.

As upper ridging noses into the region from the east on Tuesday,
we should see mostly precipitation free conditions through the end
of the week across North and Central Texas. The only exception may
be across our western counties where continued troughing over the
western U.S. could lead to some scattered showers/storms
approaching the area during the late evening hours each evening
through the end of the week. We'll keep PoPs at 10% for now given
the uncertainty in this scenario. Otherwise, it will remain hot
and humid with highs in the upper 90s and heat indices near 105
each afternoon.

Dunn

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    75  93  78  95  79 /  60  40  20  20   5
Waco                77  98  78  98  78 /  20  30  10  10   5
Paris               71  84  73  89  75 /  90  80  40  20  10
Denton              72  92  77  94  77 /  70  30  20  20  10
McKinney            73  90  76  93  77 /  70  50  20  20  10
Dallas              76  93  79  95  80 /  60  40  20  20   5
Terrell             76  91  76  94  77 /  60  50  20  20   5
Corsicana           76  94  77  95  77 /  20  30  10  10   5
Temple              76  99  77  99  76 /   5   5  10   5   5
Mineral Wells       72  94  76  96  76 /  50  20  20  20  10

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Sunday morning for TXZ092>095-105>107.

&&

26/91

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Special Weather Statement
National Weather Service Fort Worth TX
151 PM CDT SAT AUG 12 2017

TXZ105-121915-
Hunt TX-
151 PM CDT SAT AUG 12 2017

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL HUNT COUNTY UNTIL 215 PM
CDT...

At 150 PM CDT, Doppler radar was tracking a strong thunderstorm over
Caddo Mills, or near Greenville, moving east at 10 mph.

Wind gusts up to 50 mph will be possible with this storm.

Locations impacted include...
Greenville, Commerce, Caddo Mills, Campbell, Josephine and
Neylandville.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with this storm. Seek
a safe shelter inside a building or vehicle.

&&

LAT...LON 3304 9587 3296 9630 3316 9629 3329 9586
TIME...MOT...LOC 1850Z 274DEG 8KT 3308 9619

Dunn

Special Weather Statement
National Weather Service Fort Worth TX
231 PM CDT SAT AUG 12 2017

TXZ107-122000-
Hopkins TX-
231 PM CDT SAT AUG 12 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHERN HOPKINS COUNTY UNTIL 300
PM CDT...

At 231 PM CDT, Doppler radar was tracking a strong thunderstorm 9
miles southeast of Cumby, or 9 miles southwest of Sulphur Springs,
moving east at 10 mph.

Dime size hail and wind gusts of 50 to 55 mph will be possible with
this storm.

Locations impacted include...
Sulphur Springs, Cumby and Como.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with this storm. Seek
a safe shelter inside a building or vehicle.

&&

LAT...LON 3296 9566 3298 9567 3298 9586 3316 9586
      3318 9542 3296 9536
TIME...MOT...LOC 1931Z 258DEG 10KT 3303 9572

Dunn

Special Weather Statement
National Weather Service Fort Worth TX
347 PM CDT SAT AUG 12 2017

TXZ093-122115-
Grayson TX-
347 PM CDT SAT AUG 12 2017

...SIGNIFICANT WEATHER ADVISORY FOR GRAYSON COUNTY UNTIL 415 PM
CDT...

At 347 PM CDT, Doppler radar was tracking a strong thunderstorm over
Sherman, moving northeast at 15 mph.

Wind gusts of 50 to 55 mph will be possible with this storm.

Locations impacted include...
Sherman, Denison, Whitesboro, Pottsboro, Collinsville, Bells,
Knollwood, Dorchester, Eisenhower State Park, southeastern Lake
Texoma, Southmayd, Sadler and Luella.

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. Seek
a safe shelter inside a building or vehicle.

&&

LAT...LON 3389 9663 3389 9658 3385 9663 3384 9662
      3382 9658 3382 9653 3377 9650 3378 9643
      3373 9638 3354 9643 3354 9694 3380 9694
      3387 9680 3386 9678 3382 9676 3383 9671
      3386 9668 3392 9667
TIME...MOT...LOC 2047Z 210DEG 12KT 3363 9665

Dunn

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FORT WORTH TX
402 PM CDT SAT AUG 12 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0345 PM     TSTM WND DMG     3 WNW SHERMAN           33.65N  96.62W
08/12/2017                   GRAYSON            TX   PUBLIC

            1-INCH TREE LIMBS BROKEN. SHINGLES BLOWN OFF.

Special Weather Statement
National Weather Service Fort Worth TX
440 PM CDT SAT AUG 12 2017

TXZ093-094-104-122215-
Collin TX-Grayson TX-Fannin TX-
440 PM CDT SAT AUG 12 2017

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN COLLIN...
SOUTHEASTERN GRAYSON AND SOUTHWESTERN FANNIN COUNTIES UNTIL 515 PM
CDT...

At 439 PM CDT, Doppler radar was tracking a strong thunderstorm near
Van Alstyne, or 14 miles southeast of Sherman, moving east at 15 mph.

Wind gusts up to 50 mph will be possible with this storm.

Locations impacted include...
McKinney, Sherman, Anna, Van Alstyne, Howe, Whitewright, Bells, Tom
Bean, Savoy, Ector, Melissa, Trenton, Weston, Westminster and Luella.

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. Seek
a safe shelter inside a building or vehicle.

&&

LAT...LON 3364 9628 3335 9629 3327 9665 3356 9664
TIME...MOT...LOC 2139Z 255DEG 12KT 3343 9650

Dunn

Special Weather Statement
National Weather Service Fort Worth TX
651 PM CDT SAT AUG 12 2017

TXZ105-107-121>123-130045-
Kaufman TX-Van Zandt TX-Hunt TX-Hopkins TX-Rains TX-
651 PM CDT SAT AUG 12 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN HUNT...EASTERN
KAUFMAN...VAN ZANDT...HOPKINS AND RAINS COUNTIES UNTIL 745 PM CDT...

At 649 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from Commerce to Lake Tawakoni to Wills Point.
Movement was east at 20 mph.

Wind gusts up to 50 mph will be possible with these storms.

Strong thunderstorms will be near...
  Commerce around 655 PM CDT.
  Cumby around 700 PM CDT.
  Fruitvale around 710 PM CDT.
  Grand Saline around 725 PM CDT.
  Cooper Lake Park South Sulphur around 730 PM CDT.
  Como around 745 PM CDT.

Other locations impacted by these storms include Lone Oak, Point and
Tira.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Frequent cloud to ground lightning is occurring with these storms.
Seek a safe shelter inside a building or vehicle.

&&

LAT...LON 3296 9566 3272 9564 3268 9559 3248 9560
      3245 9556 3245 9628 3328 9595 3330 9586
      3322 9586 3325 9579 3330 9576 3330 9567
      3334 9562 3335 9548 3337 9542 3336 9533
      3337 9531 3296 9531
TIME...MOT...LOC 2349Z 256DEG 18KT 3327 9587 3302 9586 3268 9592 3248
9614

Dunn