Severe Thunderstorm Warning 99, NWS Fort Worth, TX

Area Forecast Discussion
National Weather Service Fort Worth TX
340 PM CDT Sat Apr 21 2018

.SHORT TERM...
A large scale upper level low pressure center will continue
eastward into the Southern Plains this evening while its
attendant surface low and cold front work their way across North
and Central Texas. After one round of showers and storms earlier
today, a second round of convection accompanying the surface low
can be seen on RADAR across the northwestern part of the forecast
area. Storms had been struggling to survive, but with surface
heating storms will increase in coverage and intensity as they
approach the I-35 corridor late afternoon/early evening.

Visible satellite imagery reveals an area of good insolation over
the western third of the region, and it will be interesting to see
how things evolve over the next few hours as storms move into the
area of increasing instability. Being that good deep layer shear
values are already in place, the current thinking is that a few
storms will become capable of producing large hail and damaging
winds as a surface based CAPE approaches 1000 J/KG. This threat
will not be wide-spread, but will likely affect areas along I-20
including the DFW Metroplex this evening. A low-end severe threat
will continue later into the evening as storms push east of
I-35/35E and south of I-20. The severe threat would most likely
shift primarily to damaging wind gusts as storms evolve into a
linear mode.

Precipitation will quickly push east and south of the forecast
area around midnight along with the cold front. Breezy conditions
can be expected during the overnight hours as northwest winds
usher in a cooler and drier airmass behind the front. Low
temperatures tonight should range from the mid 40s in the
northwest to mid 50s in the southeast.

30

&&

.LONG TERM...
/Sunday through Friday/

The upper level low that is currently over western Kansas will
have moved to just south of Fort Smith, Arkansas by 7 AM Sunday.
Clouds will decrease from southwest to the northeast during the
day but the northeastern zones will remain mostly cloudy past
sunset due to wrap around moisture from the upper level low. It
will be breezy and cool. Winds will be northwesterly at 10 to 20
mph with some gusts over 25 mph. Highs will range from the lower
60s northeast to the lower 70s across Central Texas.

Wind speeds will decrease to 5 to 10 mph Sunday night. The upper
level low will have moved across Arkansas during the day Sunday
will into the Tennessee River Valley by daybreak Monday.  Skies
across North and Central Texas will be mostly clear across all
but the northeastern zones where some wrap-around moisture from
the upper low will remain. Lows will be in the mid 40s to lower
50s.

Dry and warmer weather is expected Monday and Tuesday with mostly
sunny skies expected area wide. Highs will be in the upper 60s
northeast to the upper 70s southwest Monday and expect mid 70s
northeast to mid 80s southwest Tuesday.

A northern stream shortwave is forecast to move southeast
through the Northern and Central Plains Tuesday and Tuesday
night through the Arklatex by sunset Wednesday. The moisture
return will not be great with this shortwave, but with a cold
front expected to move into the forecast area Tuesday night and
lift above the frontal boundary Wednesday, we will have 30-50
percent PoPs for Tuesday night and Wednesday. With the increased
cloud cover and chances of precipitation, it will be cooler
Wednesday with highs in the mid 60s north to the lower 70s across
Central Texas.

The model solutions really diverge on the possibility for a late
week system. Given the low confidence have just placed 20 to 30
percent PoPs for Thursday night and Friday.

58

&&

.AVIATION... /Issued 112 PM CDT Sat Apr 21 2018/
Satellite data early this afternoon indicates a deep upper low
now moving into western portions of the Southern Plains. The
system is well-defined and producing a large precipitation shield,
which stretches from Oklahoma to south-central Texas. This
activity is composed of scattered showers and occasional embedded
thunderstorms with tops generally around 30K Ft. It has moved
east of all TAF locations and will continue pushing east into East
Texas this afternoon.

Meanwhile, a surface cyclone was located near Snyder, TX with a
dryline extending south and a Pacific front southwest from the
low center. This feature will push east through the rest of the
afternoon and will be accompanied by another round scattered
convection. The front will likely overtake the dryline as the
system encroaches on western/northwestern portions of DFW TRACON
this afternoon. It is possible that the stabilized atmosphere in
the wake of earlier showers and storms may mitigate new
development, but the timing for late afternoon and evening likely
gives us enough time to recover. The latest hi-res guidance
supports this, and is in favor of either maintaining storms as
they move in from the northwest, or generating additional storms
in the event that current activity weakens, so a TEMPO for TS in
the Metroplex centered around 00Z seems reasonable at this time.
Instability should be sufficient for a few strong to severe storms
with large hail and damaging winds possible. This threat will
continue this evening as storms move south and southeast of the
Metroplex, affecting KACT in the 01-04Z timeframe.

A shift to north winds can be expected as the front and
associated convection push through. Behind the front, MVFR cigs
will persist through much of the overnight hours. Cigs should
scatter out Sunday morning with VFR conditions the rest of the
forecast period.

30

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    51  69  51  75  55 /  60   0   0   0   0
Waco                52  71  49  77  52 /  50   0   0   0   0
Paris               51  62  52  69  51 /  70   5   5   5   0
Denton              48  67  49  73  51 /  50   0   0   0   0
McKinney            50  66  50  72  51 /  60   0   0   0   0
Dallas              50  69  53  75  55 /  60   0   0   0   0
Terrell             51  68  51  74  52 /  70   0   0   0   0
Corsicana           53  69  50  74  53 /  60   0   0   0   0
Temple              52  72  50  77  53 /  40   0   0   0   0
Mineral Wells       47  68  47  75  51 /  30   0   0   0   0

&&

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

30/58

Hazardous Weather Outlook
National Weather Service Fort Worth TX
333 PM CDT Sat Apr 21 2018

TXZ091>095-100>107-115>123-129>135-141>148-156>162-174-175-221215-
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-
333 PM CDT Sat Apr 21 2018

This Hazardous Weather Outlook is for North and Central Texas.

.DAY ONE...Tonight.
There is a chance of thunderstorms across much of North and Central
Texas this evening along a southeastward-moving cold front. A few
storms will become strong to severe, with large hail and damaging
wind gusts possible. In addition, brief heavy rain may pose a threat
for minor flooding. Storms will end from west to east late this
evening and overnight.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.
Thunderstorm chances will return to all of North and Central Texas
Tuesday night through Wednesday Night, and again Thursday night
through Friday.

.SPOTTER INFORMATION STATEMENT...
Limited spotter activation may be requested this evening south of a
line from Graham to Sulphur Springs.

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