Tornado and Flash Flooding in Texas, April 10 to 11, 2017

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1240 PM CDT Mon Apr 10 2017

.AVIATION...
A cold front currently stretches from near a MKN-MWL-GYI line
early this afternoon and is gradually progressing southeastward.
Winds ahead of this feature are incrementally veering, and a north
flow at the Metroplex airports is anticipated over the next 1-2
hours, while the true north wind shift will likely hold off until
around 20Z or thereabouts.

Thunderstorms are expected to initiate along the the aformentioned
cold front during the 1-2 PM time frame as the lingering vestiges
of our capping inversion are lifted and eroded. Given the front's
location north and west of all TAF sites, severe thunderstorms are
possible this afternoon and evening. The primary threats with
storms today will be large hail (and some hail approaching 2" is
not out of the question), along with wind gusts in excess of 50
kts. Based on the available observational and high-resolution
data, the most likely time frame for direct impacts at Metroplex
sites appears to be during the 20-23Z period, and 22-02Z at Waco.
There is some uncertainty regarding the longevity of thunder
impacts this afternoon and evening, however. Most high-resolution
guidance agrees that a consolidating cold pool will swiftly usher
this thunderstorm complex south and east of the Metroplex, and
based on this morning's upper air sounding showing plentiful dry
air aloft, this appears to be the most probable solution.
Therefore, opted to shut VCTS mention off at 11/01Z in the
Metroplex, but the threat for showers (and perhaps a sporadic
lightning strike) will persist overnight.

A similar trend may play out at Waco, but uncertainty regarding
how far south the cold pool pushes influenced the decision to hold
onto VCTS for a few more hours tonight. These timings will
continually be refined this afternoon and evening.

At all sites, MVFR cigs are expected to return this evening and
overnight as the frontal inversion begins to saturate.

Carlaw

&&

.MESOSCALE UPDATE...
Busy afternoon shaping up across North and Central TX with the
main concerns being potential for severe convection and flash
flooding. The morning upper air balloon data across the region
revealed a continued weakening of the cap across North and Central
TX. Experimental satellite imagery coupled with regional radar
observations also indicate some shallow convection has been
persistent along and south of a slow moving frontal boundary
located from near Comanche to DFW to Gainesville line. Another
interesting feature was a band of low level confluence just west
of the I-35 corridor across the Hill Country. This north-south
oriented band will likely continue to lift northward as the low
level southerly flow continues.

Overall expectations for this afternoon remain mostly similar to
previous forecasts. In house convective parameters indicate that
instability continues to climb with additional diabatic heating.
Much of the area in the warm sector is characterized by MLCAPE
values of around 2000 J/kg. Inhibition immediately south and east
of the front continues to fall rapidly with values approaching
near zero, indicating that the cap strength will likely become
negligible over the next 1-2 hours. With ample convergence along
the well-defined synoptic front and aformentioned confluence band,
thunderstorms should erupt in the 1-3 PM time frame. The primary
storm modes this afternoon will be brief supercellular structures
and multicell complexes. Sustained updrafts will have the
capability to produce large hail and some forecast sounding
analogs indicate that a risk for hail up to 2" in diameter will
not be out of the question. In addition, increasing T-Td spreads
coupled with dry mid-levels will facilitate a damaging wind risk,
especially if storms congeal into a larger complex. The tornado
risk may be largely mitigated by modest low level wind fields and
a potential for non-constructive storm scale interactions. That in
mind, we will have to monitor the tornado potential as we do have
a large scale synoptic boundary in the vicinity of storms. Most
hi- res guidance is consistent on developing a large cold pool
which may promote upscale growth into one ore more smaller line
segments. The best risk for severe storms this afternoon will be
for areas along and east and southeast of the aformentioned line
(Comanche to DFW to Gainesville)

Last, but not least, sufficient low level moisture juxtaposed with
decent rainfall over the last week or so will support an
appreciable flash flood risk. As a result, we elected to issue a
flash flood watch for roughly the southern half of our forecast
area. While overall rainfall amounts will be in the 1-3" range
with isolated 4" totals, rainfall rates will likely promote flash
flooding across parts of Central Texas.

Additional storms will be possible during the overnight hours as
ascent atop the cold front/cold pool will continue. A few hi-res
models also depict this scenario quite well. The main risk with
these storms will be hail and additional heavy rain which may
aggravate any ongoing flood issues.

24-Bain

&&

.PREV DISCUSSION... /ISSUED 346 AM CDT Mon Apr 10 2017/
Thunderstorms currently rumbling across Missouri and Iowa are
being generated by a strong shortwave trough moving across the
Northern Plains. The eastward progression of the shortwave will
help push a cold front southeast into North and Central Texas
in the next few hours. The front stretched from Lubbock to
Topeka, KS early this morning, and will serve as a focus for
convection as it sags deeper into the forecast area later today.

A persistent warm layer at 850 MB will keep the atmosphere capped
through most of the morning. The cap is forecast to erode,
however, around midday as good surface heating takes place and the
front makes its presence known. Convective initiation along the
front should occur around noon as it encroaches on the Interstate
20 corridor. The highest POPs today will be across the
southeastern half of the forecast area, or along and southeast of
the front, with POPs decreasing as you go northwest. The latest
high resolution guidance suggests that the surface boundary will
be somewhere in the vicinity of a Bonham-Fort Worth-Goldthwaite
line when the cap breaks and convection ensues. Storms may develop
rapidly in a highly unstable environment and could become severe
with large hail and damaging winds.

The surface front is progged to pull up stationary near a Paris-
Lampasas line late this afternoon. As storms continue to fire
along the boundary, a cold pool is likely to develop and push
gradually south with time. Moisture pooling along the gust front
will lead to PWATs increasing to 1.75" across the southern
counties this evening. After collaborating with neighboring
offices we have increased QPF during the 00-06Z timeframe in the
Waco-Temple and surrounding areas where the heaviest rain is
likely. There is no plan for a flood watch at this time, as the
current thinking is that the cold pool will progress south fast
enough to preclude widespread heavy rain and flooding.

While convection continues to push south overnight, a southern
stream shortwave trough will move quickly across the region, which
may lead to additional convective development near the remnants
of the stationary front. We will keep POPs going overnight across
most of the region, with the highest POPs across the south and
lowest across the northwest. Precipitation will taper off from
northwest to southeast during the day Tuesday as the southern
stream shortwave moves east into the MS Valley.

A shortwave ridge will build overhead as the trough heads east,
which should keep things precipitation-free late Tuesday and early
Wednesday. Lingering moisture and instability could lead to some
diurnally driven convection Wednesday afternoon, though coverage
should remain fairly isolated. Another weaker shortwave will lift
northeastward out of Mexico across West Texas on Thursday, which
could generate mainly isolated storms across the west and
northwest counties late Thursday into Friday. Saturday and early
Sunday look dry at this time, then the next West Coast trough
leads to more storm chances late Sunday and next Monday.

30

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    78  59  72  62  79 /  60  50  40  10  20
Waco                79  63  75  62  79 /  60  60  50  20  20
Paris               74  59  71  59  75 /  60  60  50  10  20
Denton              77  56  72  59  77 /  50  50  40  10  20
McKinney            77  57  72  60  76 /  60  60  40  10  20
Dallas              78  61  73  63  79 /  60  60  50  10  20
Terrell             78  61  73  61  78 /  60  60  50  20  20
Corsicana           79  63  73  62  78 /  60  60  50  20  20
Temple              80  64  74  62  78 /  60  60  50  20  20
Mineral Wells       76  57  72  58  77 /  40  40  30  10  20

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Tuesday morning for TXZ135-142>148-
156>162-174-175.

&&

90/79

Hazardous Weather Outlook
National Weather Service Fort Worth TX
1122 AM CDT Mon Apr 10 2017

TXZ091>095-100>107-115>123-129>135-141>148-156>162-174-175-111145-
Montague-Cooke-Grayson-Fannin-Lamar-Young-Jack-Wise-Denton-Collin-
Hunt-Delta-Hopkins-Stephens-Palo Pinto-Parker-Tarrant-Dallas-
Rockwall-Kaufman-Van Zandt-Rains-Eastland-Erath-Hood-Somervell-
Johnson-Ellis-Henderson-Comanche-Mills-Hamilton-Bosque-Hill-Navarro-
Freestone-Anderson-Lampasas-Coryell-Bell-McLennan-Falls-Limestone-
Leon-Milam-Robertson-
1122 AM CDT Mon Apr 10 2017

This Hazardous Weather Outlook is for North and Central Texas.

.DAY ONE...This Afternoon and Tonight.
There is a chance of thunderstorms across all of North and Central
Texas today. Some storms this afternoon and tonight may become
severe with the greatest threat along and southeast of a Comanche to
Granbury to Muenster line. The main hazards from storms will be
large hail and strong winds, although an isolated tornado cannot be
ruled out today.

There is also a risk for heavy rainfall from thunderstorms which is
expected to lead to flash flooding. As a result, a flash flood watch
is in effect from 2 PM CDT this afternoon through Tuesday morning
for locations along and south of a Goldthwaite to Hillsboro to Athens
line.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.
There will be a chance of thunderstorms area wide Tuesday and
southeast of a Goldthwaite to Sulphur Springs line Tuesday night, and
a flash flood watch is in effect through Tuesday morning.

Low chances of thunderstorms will linger, periodically, across parts
of the region Wednesday through Friday. The severe weather threat
appears low at this time with cloud to ground lightning being the
main hazard with any storms.

Thunderstorms chances will return area wide Sunday.

.SPOTTER INFORMATION STATEMENT...
Spotter activation may be requested this afternoon and tonight along
and southeast of a Comanche to Granbury to Muenster line.

Special Weather Statement
National Weather Service Fort Worth TX
206 PM CDT MON APR 10 2017

TXZ118-131-133-101930-
Hood TX-Tarrant TX-Johnson TX-
206 PM CDT MON APR 10 2017

...SIGNIFICANT WEATHER ADVISORY FOR JOHNSON...SOUTHERN TARRANT AND
NORTHEASTERN HOOD COUNTIES UNTIL 230 PM CDT...

At 206 PM CDT, Doppler radar was tracking a strong thunderstorm over
Godley, or 8 miles northwest of Cleburne, moving northeast at 35 mph.

Dime size hail and wind gusts up to 45 mph will be possible with
this storm.

Locations impacted include...
Fort Worth, Arlington, Grand Prairie, Mansfield, Burleson, Cleburne,
Crowley, Forest Hill, Kennedale, Everman, Keene, Joshua, Alvarado,
Rendon, Pecan Plantation, Venus, Godley, Cross Timber and Briaroaks.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so closely monitor for additional
information or possible warnings from the National Weather Service.

&&

LAT...LON 3255 9764 3255 9755 3263 9755 3265 9725
      3265 9704 3255 9704 3255 9709 3236 9709
      3225 9761 3232 9761 3232 9764
TIME...MOT...LOC 1906Z 231DEG 29KT 3241 9753

24-Bain

Special Weather Statement
National Weather Service Fort Worth TX
215 PM CDT MON APR 10 2017

TXZ103-104-101945-
Collin TX-Denton TX-
215 PM CDT MON APR 10 2017

...SIGNIFICANT WEATHER ADVISORY FOR EASTERN DENTON AND WESTERN COLLIN
COUNTIES UNTIL 245 PM CDT...

At 215 PM CDT, Doppler radar was tracking a strong thunderstorm over
Lewisville, moving northeast at 35 mph.

Nickel size hail and winds of up to 40 mph will be possible with
this storm.

Locations impacted include...
Plano, McKinney, Carrollton, Frisco, Denton, Lewisville, Allen,
Flower Mound, Coppell, The Colony, Southlake, Corinth, Highland
Village, Trophy Club, Lake Dallas, Lake Lewisville, Little Elm,
Prosper, Anna and Fairview.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so closely monitor for additional
information or possible warnings from the National Weather Service.

&&

LAT...LON 3340 9639 3314 9655 3299 9681 3299 9724
      3342 9697
TIME...MOT...LOC 1915Z 230DEG 29KT 3308 9698

24-Bain

Special Weather Statement
National Weather Service Fort Worth TX
219 PM CDT MON APR 10 2017

TXZ131-132-101945-
Hood TX-Somervell TX-
219 PM CDT MON APR 10 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOMERVELL AND SOUTHEASTERN HOOD
COUNTIES UNTIL 245 PM CDT...

At 219 PM CDT, Doppler radar was tracking a strong thunderstorm over
Dinosaur Valley State Park, or 11 miles south of Granbury, moving
northeast at 15 mph.

Dime size hail and winds up to 40 mph will be possible with this
storm.

Locations impacted include...
Pecan Plantation, Glen Rose and Dinosaur Valley State Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so closely monitor for additional
information or possible warnings from the National Weather Service.

&&

LAT...LON 3249 9762 3220 9761 3220 9764 3209 9786
      3228 9797
TIME...MOT...LOC 1919Z 234DEG 15KT 3227 9778

24-Bain

Special Weather Statement
National Weather Service Fort Worth TX
236 PM CDT MON APR 10 2017

TXZ118-131>133-102000-
Hood TX-Tarrant TX-Johnson TX-Somervell TX-
236 PM CDT MON APR 10 2017

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN SOMERVELL...
JOHNSON...SOUTH CENTRAL TARRANT AND EAST CENTRAL HOOD COUNTIES UNTIL
300 PM CDT...

At 236 PM CDT, Doppler radar was tracking a strong thunderstorm near
Cleburne, moving northeast at 30 mph.

Dime size hail and winds of up to 40 mph will be possible with this
storm.

Locations impacted include...
Fort Worth, Arlington, Mansfield, Burleson, Cleburne, Crowley, Forest
Hill, Kennedale, Everman, Keene, Joshua, Alvarado, Rendon, Pecan
Plantation, Venus, Glen Rose, Godley, Cross Timber, Cleburne State
Park and Briaroaks.

LAT...LON 3245 9764 3270 9719 3255 9708 3255 9709
      3238 9709 3221 9761 3227 9779
TIME...MOT...LOC 1936Z 236DEG 28KT 3241 9743

24-Bain

Special Weather Statement
National Weather Service Fort Worth TX
239 PM CDT MON APR 10 2017

TXZ094-095-102030-
Lamar TX-Fannin TX-
239 PM CDT MON APR 10 2017

...SIGNIFICANT WEATHER ADVISORY FOR WEST CENTRAL LAMAR AND NORTHERN
FANNIN COUNTIES UNTIL 330 PM CDT...

At 239 PM CDT, Doppler radar was tracking a strong thunderstorm over
Ravenna, or near Bonham, moving northeast at 25 mph.

Dime size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Bonham, Savoy, Ector and Ravenna.

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.

This storm may intensify, so closely monitor for additional
information or possible warnings from the National Weather Service.

&&

LAT...LON 3384 9584 3386 9579 3372 9581 3354 9622
      3354 9638 3372 9638 3369 9636 3370 9634
      3370 9632 3377 9629 3375 9619 3381 9618
      3384 9615 3384 9605 3386 9603 3384 9602
      3386 9599 3387 9600 3386 9595 3389 9593
TIME...MOT...LOC 1939Z 234DEG 23KT 3365 9621

24-Bain

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FORT WORTH TX
241 PM CDT MON APR 10 2017

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

0238 PM     HAIL             THE COLONY              33.09N  96.89W
04/10/2017  E0.75 INCH       DENTON             TX   EMERGENCY MNGR

            HAIL PEA TO DIME SIZED IN THE COLONY