Flash Flooding and Hail in Texas, June 19 to 20, 2019

Area Forecast Discussion
National Weather Service Fort Worth TX
324 PM CDT Wed Jun 19 2019

.SHORT TERM...
/Through Tonight/

Key Messages:
-Thunderstorms are expected to begin developing, initially
 northeast of the Dallas/Fort Worth Metropolitan Area, after 4:00
 PM this afternoon.
-Thunderstorms will continue to develop back to the southwest,
 with the highest storm chances expected in the Metroplex after
 7:00 PM.
-Some severe thunderstorms are likely, with large hail (perhaps
 greater than two inches in diameter) and damaging wind gusts in
 excess of 60 MPH being the main hazards.
-A tornado threat will exist as well, with the greatest tornado
 threat expected to exist from 5-8 PM, generally near and
 northeast of Dallas.
-While significant flash flooding is unlikely, some localized
 flooding may be possible in urban areas.

The main story for the short-term forecast will be the convective
chances (and severe weather chances) through the period. At
present time, a 1007 mb surface low is located over West Texas,
with a cold front running back to the northeast across Oklahoma
and into the Missouri River Valley. A dryline extends from the
surface low back to the southwest towards Big Bend National Park.
The warm sector is characterized by a very warm, moist, and
unstable air mass. As of this writing, DFW is 91/75 and Waco is a
sweltering 95/75. While these temperatures and dewpoints are not
entirely atypical for mid June in North and Central Texas, what is
unusual is that per the special 19Z RAOB out of Fort Worth, very
steep mid-level lapse rates are present (8.5 C/km). The result of
this combination is a highly unstable air mass with MLCAPE values
approaching 4000 J/kg. Upper-level flow is impressive too, with
effective bulk shear values approaching 60 KT on the 19Z RAOB.

High-resolution model guidance is in good agreement that
convection should initiate over our northeastern counties to
begin, probably some time between 4 p.m. and 6 p.m. Storms should
begin to the northeast of DFW, and then back-build to the
southwest through the evening. The most likely time for
thunderstorms in the core of the Metroplex (i.e. Collin, Dallas,
Denton, and Tarrant) will be probably be after 7 p.m.
Thunderstorms should progress southeast through the evening, and
should taper off after 3 a.m.

Given the aforementioned high levels of instability and strong
wind shear, any thunderstorms that develop will likely become
severe. Steep mid-level lapse rates and large instability will
result in a risk for large hail (with significant hail, i.e.
larger than two inches in diameter, not out of the question). With
time, shear vectors oriented nearly parallel to the approaching
cold front should allow convection to grow upscale into a
mesoscale convective system (MCS). While the large hail threat
will likely continue, a damaging wind threat will exist as well.
Severe wind gusts in excess of 60 MPH will be likely in the
stronger convective cores. Finally, with regards to the tornado
potential, instability is actually a bit limited in the lowest 3
km of the atmosphere, and low-level flow is not particularly
strong, both of which may limit the tornado potential. With that
being said, total instability is very strong, and deep layer
shear is certainly high enough to support some rotating
thunderstorms, particularly during the initial phases while
thunderstorms remain somewhat discrete.

With regards to heavy rain potential, precipitable water values on
the 19Z sounding were around 1.65 inches, which is not
particularly impressive, but sufficient enough to result in heavy
rainfall in the more intense convective cores. Storms should also
move at a fairly decent speed (30+ MPH) limiting the potential for
widespread flash flooding. Having said that, if we were to get any
training of thunderstorms, particularly over urban areas, a
localized flooding threat could develop.

Finally, into Central Texas, thunderstorm activity may be more
limited, but some isolated to widely scattered storms may still be
possible late this evening. Because of concerns regarding
coverage, the severe weather threat will be lower here, but any
storms that do develop will have to the potential to become
severe.

37

&&

.LONG TERM...
/Thursday and beyond/

Summary: Hot and humid conditions will continue to be of concern
through the end of the week. Low thunderstorm chances will also
continue through early next week, but not everyone will see rain
each day. The best chances will be Sunday into Monday.

Most of the region will be rain-free on Thursday, but the far
western counties will have a low potential for thunderstorms.
Both the GFS and ECMWF are hinting at the dryline across the Big
Country bulging far enough eastward to where thunderstorms may
develop and affect the far western counties Thursday afternoon.
Model soundings reveal a mostly capped environment, but given the
hot afternoon temperatures, a downburst wind threat will exist if
thunderstorms do initiate along the dryline. With 850 mb
temperatures in excess of 25C across the region, afternoon
temperatures will range from the mid 90s along the Red River to
near or just above the century mark across the west. The hot
temperatures, in combination with dewpoint values in the low to
mid 70s, will have heat index values ranging from 104 to 110, with
the highest values being across Central Texas. A limiting factor
on whether the higher values will be reached or exceeded is the
evolution of convection from Wednesday evening... so the Heat
Advisory will remain confined across the southeastern counties.

Weak disturbances will track across the region as an upper level
trough deepens across the western US, and in combination with
ample moisture, there may be scattered thunderstorms on Friday
and Saturday. Friday will feature another hot and humid day with
high temperatures similar to Thursday, and may necessitate a Heat
Advisory. The best chances for showers and thunderstorms will be
Sunday into Monday as a shortwave tracks east across the Central
Plains. Guidance has hinted at a weak front being an area of
focus for convection across Oklahoma, which may slide south
towards North Texas Sunday night. Mid week rain chances may start
to wind down as upper level ridging sets up across the west.
Otherwise, highs will be in the low to mid 90s this weekend and
early next week.

Garcia

&&

.AVIATION... /Issued 100 PM CDT Wed Jun 19 2019/
/18Z TAFs/

Primary concern continues to be convective potential this evening
into tonight. Some MVFR potential remains for tomorrow morning as
well.

Through 19Z or so, occasional MVFR CIGs could persist, primarily
around KDAL, where low-level mixing is not quite as strong.
Regardless, all sites should be VFR by approximately 19Z. Through
this evening, south/southwest winds around 15 kt should
develop/continue, and occasional gusts to 20-25 kt will be
possible.

Convection likely develops across parts of North Texas by 21-23Z.
The most likely area for initial development appears to be across
northeast Texas, perhaps initially impacting the Bonham
cornerpost. Convection should gradually develop closer to
Metroplex terminals by 23Z, likely resulting in significant
impacts. The strongest storm cores will be capable of gusts
upwards of 50 kt (most likely from a westerly direction), but
confidence in this occurring at any one terminal is far too low to
include in TAFs. Otherwise, hail, very heavy rain rates, and
frequent lightning are expected with this convection. Cells should
shift east of terminals around 03-04Z, but some uncertainty
exists in the cessation time. TAF amendments will likely be
needed.

Confidence remains too low for TEMPO TS at KACT, but that could be
introduced in later amendments.

Brief MVFR possible at all sites around 13-15Z tomorrow, before
moisture mixes out. Winds increase from the south thereafter.

Picca

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    74  97  77  96  77 /  60  10  10   0  20
Waco                75  99  77  98  77 /  40   5   5   0  10
Paris               71  92  75  92  76 /  80  10  10   5  10
Denton              71  97  77  95  77 /  60  10  10   5  20
McKinney            71  96  77  95  77 /  80  10  10   0  10
Dallas              75  97  77  96  78 /  60  10  10   0  20
Terrell             74  97  77  96  77 /  60   5  10   0  10
Corsicana           75  95  76  93  76 /  60   5   5   0  10
Temple              74  99  77  98  77 /  40  10  10   5  10
Mineral Wells       70  99  75  96  75 /  50  10  10   5  20

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT Thursday for TXZ135-146>148-157>162-
174-175.

&&

22/37

Hazardous Weather Outlook
National Weather Service Fort Worth TX
326 PM CDT Wed Jun 19 2019

TXZ091>095-100>107-115>123-129>135-141>148-156>162-174-175-201200-
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-
326 PM CDT Wed Jun 19 2019

This Hazardous Weather Outlook is for North and Central Texas.

.DAY ONE...Tonight.

Strong to severe thunderstorms are likely to develop late this
afternoon, near and to the northeast of the Dallas/Fort Worth
Metropolitan Area. The primary hazards will be very large hail and
damaging to possibly destructive winds. There will also be a risk for
tornadoes, namely for thunderstorms near any residual boundaries.
Heavy rainfall may result in localized flooding, particularly in
urban areas.

Late tonight, the risk for strong to severe storms will shift into
Central and East Texas. The main hazards will be large hail and
damaging winds.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Hot conditions are expected again on Thursday...especially across
Central Texas. Heat index values may climb to near or just above
105 degrees.

After a break in storm chances on Friday, more scattered
thunderstorms are possible over the upcoming weekend.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be requested over most of North and
parts of Central Texas.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FORT WORTH TX
226 PM CDT WED JUN 19 2019

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

0345 PM     TORNADO          1 E FARMERS BRANCH      32.92N 96.87W
06/16/2019                   DALLAS             TX   NWS STORM SURVEY

            A BRIEF TORNADO IS BELIEVED TO HAVE MOVED
            NORTHWEST ACROSS PART OF FARMERS BRANCH NEAR
            THE JOHNSON`S OUTPOST YMCA ON VALLEY VIEW
            LANE. PART OF THE ROOF WAS TORN OFF OF THE
            BUILDING AND THE ROOF WAS BLOWN TO THE
            NORTHWEST. OTHER TREE DAMAGE WAS NOTED
            STRETCHING TO THE NORTHWEST INTO THE NEARBY
            NEIGHBORHOOD.

&&