Special Weather Statement, NWS Fort Worth, TX

Area Forecast Discussion
National Weather Service Fort Worth TX
1259 PM CDT Mon Apr 17 2017

.AVIATION...
/18Z TAFS/

We continue to monitor a slow-moving storm cluster and outflow to
the north of DFW area airports early this afternoon. In addition,
we are monitoring a convective MCV over South-Central Texas
between San Antonio and Austin that "may" have an effect on Waco
late today into this evening. Challenges, due to mesoscale-driven
convection will be timing and cigs, as well as weak chaotic light
flow tonight and IFR/LIFR cigs and possible fog.

We are still awaiting some sort of cold pool from the locally
heavy rains up north to shift convection southward into DFW,
though some isolated activity has already occurred with the mid
April sun working upon a moist and unstable atmosphere. East-
southeast winds have been maintaining 10 knots or less, but could
see gusts 30-35 knots in and near any storm activity through the
afternoon hours around the DFW Metro airports, before weakening
and shifting south of the area by early this evening. This is
stated with not the greatest confidence, due to the aforementioned
lack of steering flow aloft and mesoscale influences. Overnight,
variable winds 5 knots or less and a moist surface to boundary
layer may lend to some IFR/LIFR cigs with vsbys 1-3SM. We should
know later the extent of any fog and low stratus as this
convective system evolves.

Waco should remain under VFR cigs and be convection-free until
either outflow from the north makes it down there very late this
afternoon, or if the slow-northeast moving MCV over South Central
Texas moves close by and just southeast of the airport. Unlike DFW
area airports, I did not introduce any categorical convective
periods and held to VCTS with so much uncertainty involved.
Similar to DFW though, some LIFR/IFR cigs and fog could develop
between midnight and sunrise Tuesday morning, though this will all
be contingent on mesoscale system and storm evolution and if
convective activity can or cannot mix out the surface-boundary
layer moisture. Expect several adjustments and amendments through
tonight on evolution of both convection and stratus/fog.

&&

.UPDATE...
Another complex weather scenario will be unfolding today, although
it would appear Convective Allowing Models (CAMs) have a little
better handle on the situation than they did yesterday given
somewhat better defined mesoscale forcing mechanisms. The first
feature of interest is an overnight MCS which has exhausted an
outflow boundary, presently arcing from near a Jacksboro to Denton
to Rockwall line and heading southward. While low-level winds
remain relatively weak (our morning balloon sampled winds in the
925-850 mb layer of only 15-25 kts), this appears to be sufficient
at regenerating convection along and behind the boundary as
evidenced by recent radar mosaic imagery. Mesoanalysis shows that
only limited (if any) convective inhibition remains thanks to
dewpoints in the mid and upper 60s and it won't take much heating
at all to allow for additional thunderstorm development through
the afternoon hours. As we've seen already, these storms are
capable of some locally very heavy rainfall rates (a RAWS site in
far northeastern Fannin County earlier recorded nearly 5 inches of
rainfall over the span of about 4-5 hours, with 6.38" since rain
began falling). As a result, localized flash flooding appears
possible this morning and into the afternoon, but it appears
forward propagation should increase later this afternoon as a
deeper cold pool gets going.

The second area of interest is a diffuse area of low pressure just
east of Frederick, Oklahoma this hour. Thunderstorms have begun
developing near this feature recently, and high resolution
guidance suggests yet another cluster of storms may congeal here
today, eventually surging into our northwestern counties later
this afternoon and evening. This appears to be a plausible
scenario, with forward propagating Corfidi Vectors keying in on
this direction of movement.

Finally, a vorticity maximum across the Hill Country associated
with yet another overnight MCS, is forecast to track
northeastward, potentially clipping our southern counties today.
The recently-upgraded 3 km NAM and, to a degree, the HRRR and ESRL
HRRRX all seem to be keying in on this feature as an additional
focus for thunderstorms this afternoon and evening.

All of that to say: we've increased PoPs with this morning update
into the likely category across basically all of the forecast
area, highest near the I-20 corridor and points north and east.
While widespread severe weather is not anticipated, plenty of
DCAPE (especially out west) and CAPE through the hail growth zone
mean strong downburst winds and small hail will be possible, even
with the meager flow today. We will evaluate the flash flood
threat today, but if cold pools can get organized as anticipated,
activity should move along enough to temper this threat.

Carlaw

&&

.PREV DISCUSSION... /ISSUED 342 AM CDT Mon Apr 17 2017/
Convection continues to fire early this morning due to two
separate pieces of energy. The first is a shortwave over South
Texas which is fueling a complex of storms in that region. The
second subtle shortwave is approaching the Central Plains and is
supplying weak large scale lift to aid in the life of the linear
MCS currently across Oklahoma and Arkansas. North Texas will not
see any direct impacts from these two upper features. However, it
will remain moist and unstable over the region through the day so
scattered convection is likely to develop, especially on any
outflow boundaries that wander into the region. The most likely
place for this to happen will be across the northern zones due to
a developing cold pool across the Central Plains. The South Texas
complex may have the reverse effect and actually modify/hinder
moisture moving into the region. Since there are opposing factors
at work here, we will keep PoPs in the chance category for all but
the Red River zones. The severe threat looks low overall due to
unfavorable wind profiles. However, small hail and gusty winds
will be possible with the stronger storms due to moderate
instability in place. The bigger threat will actually be from
locally heavy rainfall due to weak steering flow and adequate
precipitable water values.

Shower and thunderstorm chances will slowly end from west to east
tonight as weak large scale subsidence develops behind the
departing shortwaves. While the northern wave will move relatively
quickly, the southern wave will take its sweet time and linger
over the Upper Texas Coast on Tuesday. Therefore, we will leave
some low PoPs across the eastern zones through Tuesday.

Weak upper level high pressure will fill in across the state
Tuesday night and remain in place through Thursday, resulting in
warm and rain-free weather. High temperatures will be mainly in
the 80s with lows in the 60s.

The upper ridge will shift to the east Thursday night/Friday as a
strong southern branch upper trough moves into the Central
Rockies. The latest model runs of the GFS and ECMWF keep the bulk
of the energy with this system across the Central Plains but do
move the attendant cold front through North Texas Friday night
through Saturday. There should be plenty of moisture and
instability for showers and thunderstorms beginning Thursday
night. Storms chances will increase with the arrival of the cold
front Friday night and end from northwest to southeast Saturday.
It still appears that there will be some severe storms with this
system most likely in the form of a squall line Friday night/
Saturday morning.

Once the cold front moves through the region, much cooler and
drier air will filter in Saturday night through Sunday. Highs
Saturday and Sunday will be mainly in the lower 60s with lows
Saturday night from the middle 40s to the middle 50s.

79

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    79  64  83  65  85 /  70  20   5   5   0
Waco                82  62  82  64  84 /  60  30  20  10   0
Paris               73  62  80  62  83 / 100  30  20   5   0
Denton              78  62  82  63  85 /  80  20   5   0   0
McKinney            78  62  81  64  83 /  90  20  10   5   0
Dallas              79  65  83  66  85 /  70  20   5   5   0
Terrell             79  63  82  64  84 /  70  20  10  10   0
Corsicana           80  64  82  64  83 /  70  30  20  10   0
Temple              81  62  81  64  84 /  60  30  20  10   0
Mineral Wells       82  61  83  62  86 /  70  20   5   0   0

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
None.
&&

/90

Hazardous Weather Outlook...UPDATED
National Weather Service Fort Worth TX
1151 AM CDT Mon Apr 17 2017

TXZ091>095-100>107-115>123-129>135-141>148-156>162-174-175-181215-
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-
1151 AM CDT Mon Apr 17 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. The highest chances early this afternoon will be near
and north of the I-20 corridor, and then gradually shifting south of
I-20 and into portions of Central Texas later this afternoon and
evening. A few storms could become strong with gusty downburst winds
and small hail, but with negligible wind shear, the threat of
widespread severe storms is low. These weak steering currents will
result in slow-moving storms that will be capable of heavy rainfall
leading to localized flash flooding.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.
Thunderstorm chances will end on Tuesday as the upper disturbances
responsible for this recent bout of unsettled weather move east of
the region.

A cold front will approach the Red River Thursday night and Friday,
bringing a chance of thunderstorms to areas mainly north of the I-20
corridor. The storm chances will increase Friday night into Saturday
as a strong storm system swings through the Plains and a cold front
surges through North and Central Texas. A line of storms may
accompany the front. Some of these storms could be severe.

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected at this time.

Special Weather Statement
National Weather Service Fort Worth TX
227 PM CDT MON APR 17 2017

TXZ117-118-172015-
Parker TX-Tarrant TX-
227 PM CDT MON APR 17 2017

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN PARKER AND
NORTHWESTERN TARRANT COUNTIES UNTIL 315 PM CDT...

At 227 PM CDT, Doppler radar was tracking a strong thunderstorm 7
miles southwest of Springtown, or 8 miles north of Weatherford,
moving east at 20 mph.

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

Locations impacted include...
Fort Worth, Weatherford, Saginaw, Azle, Sansom Park, Lake Worth,
Eagle Mountain, Briar, Pecan Acres, Willow Park, Reno, Blue Mound,
Pelican Bay, Lakeside, Newark and Sanctuary.

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 3299 9763 3299 9738 3282 9732 3276 9779
      3292 9784 3292 9768 3300 9765
TIME...MOT...LOC 1927Z 254DEG 18KT 3287 9774

05

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FORT WORTH TX
233 PM CDT MON APR 17 2017

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

1235 PM     HAIL             JERMYN                  33.27N  98.38W
04/17/2017  E1.25 INCH       JACK               TX   PUBLIC

            DELAYED REPORT: QUARTER TO HALF DOLLAR SIZE HAIL
            REPORTED IN JERMYN

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FORT WORTH TX
235 PM CDT MON APR 17 2017

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

0200 PM     FLASH FLOOD      DALLAS                  32.77N  96.78W
04/17/2017                   DALLAS             TX   PUBLIC

            DELAYED REPORT: HIGH WATER IN HIGHWAY, HEAVY RAIN ON 183
            WB/35E.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FORT WORTH TX
250 PM CDT MON APR 17 2017

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

0241 PM     FLASH FLOOD      PARADISE                33.15N  97.65W
04/17/2017                   WISE               TX   TRAINED SPOTTER

            STREET FLOODING FM 2123 & SUNFLOWER RD IN SW WISE COUNTY
            (PARADISE). STILL PASSABLE AT THIS TIME

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FORT WORTH TX
252 PM CDT MON APR 17 2017

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

0249 PM     FLASH FLOOD      BRIDGEPORT              33.22N  97.77W
04/17/2017                   WISE               TX   AMATEUR RADIO

            STREET FLOODING ON 9TH ST AND TURKEY CREEK TRAIL IN
            BRIDGEPORT. NOT PASSABLE

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