Area Forecast Discussion
Issued by NWS Dallas/Fort Worth, TX

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FXUS64 KFWD 200503

Area Forecast Discussion
National Weather Service Fort Worth TX
1203 AM CDT Sat May 20 2017

Convection has finally surged eastward in response to a shortwave
trough kicking northeastward across Northwest Texas. This has also
given a cold front a bit of a southeastward push, which should
help fill in the gap in the convection from north of the Metroplex
to the Red River. Since activity is now more progressive, a gusty
wind threat will be the main weather hazard along with frequent
lightning. Storms will push east of the Dallas-Fort Worth area in
the next few hours. Waco may get a bit of a reprieve later
tonight, but then additional rounds of precipitation will be
likely across KACT during the Saturday morning hours as the front
pulls up stationary.



The tornado threat has shifted north of the Red River where
numerous ongoing storms have occasionally produced tornadoes.
There is a break in the activity from the Red River down to about
I-20, then a loosely organized linear MCS is trying to get going
from south of Mineral Wells to near Lampasas. The current feeling
is that we may see showers and storms increase in coverage again
overnight as a front makes its way southeast into the area and
stronger lift from the Colorado upper low spreads farther east.
The severe threat should see a general decrease as we lose diurnal
instability, though a few storms could still pose a hail and
damaging wind threat. In fact the storms moving in on the
Metroplex from the west are showing signs of gusting out and and
possibly generating some damaging straight line winds, so please
keep an eye on any warnings issued for your area. For now there
are no watches in effect due to the isolated nature of severe
convection, though an occasional warning will remain possible for
any storms which intensify. Showers and storms will linger across
the southern counties Saturday morning as the front eases slowly
south of I-20, with locally heavy rain becoming a greater threat.



.PREV DISCUSSION... /ISSUED 225 PM CDT Fri May 19 2017/
Our slow-moving upper low continues to shift east across CO this
afternoon, with disturbances active within strong southwest flow
aloft over the western half of the state of TX. Shortwave energy
will continue to round the base of the upper low across the state
and northeast across OK through the weekend. At the surface, a
surface low was located between Midland and Lubbock, with a surface
cold front progressing southward across the OK/TX Panhandles. This
feature will be an additional player in convective developing late
tonight and lingering across Central TX later on Saturday and
possibly into Saturday night.

A corridor of enhanced isentropic lift and jet forcing aloft
remains centered from West-Central TX, northeast across the South
Plains and into southern and eastern OK this afternoon. Per latest
high res model guidance (3km NAMNEST the best on initialization
w/the HRRRx a close second), we expect our main threat through
early evening to remain west of I-35 and particularly north of
I-20. Model sounding forecasts across this area indicate plenty of
available instability(including mid level lapse rates 7-8 deg
C/km) and wind shear for severe storms containing very large hail
at times, along with damaging winds. Initial curved hodographs in
the lowest 5-10 kft do indicate a window of tornadic potential
through at least mid evening, especially with any discrete
activity, along with ample, sub-cloud instability to draw
horizontal vorticity surface upward into any rotating updrafts.

As the cold front enters our northwest CWA mid-late evening,
early indications are that discrete severe storms could congeal
into a slow, east-southeast moving QLCS or broken squall line
through the overnight hours, before weakening around daybreak
Saturday morning. The slow-movement of the cold front, along with
potential training of convection, heavier rain rates within an
area of 1.5 or greater PWATs will likely result in between 1-3
inches of rainfall along and north of I-20. We can`t rule out
isolated higher amounts. Since we`re so close to the event and
with some uncertainty on rainfall amounts, a Flash Flood Watch
will not be hoisted. That said, localized flash flooding is
certainly possible tonight and early Saturday, especially urban
areas around the DFW Metroplex, northeast through Sherman/Denison.

The surface cold front, assisted by storm outflow and the gradual
eastward progression of the upper low across the Central Plains
will continue to progress the front through Central TX during the
day Saturday into Saturday night. Better rain and convective
chances will accompany the cold front southward into East and
Central TX during this time. A few strong to severe storms are
possible where any instability can establish itself, though
coverage of severe weather should be much less than recent days.
In addition, better ascent and wind shear will be north of the
region, lessening the large-scale ascent across the area.
Depending on how fast the cold front moves southeast, areas of
heavy rain and flooding potential are uncertain. If the front is
slower, then more potential for heavier rains will exist. If the
front is more progressive, then flooding will be less likely
across Central Texas Saturday and Saturday night.

Drier low level air should continue to filter into the region
from the north the latter half of the weekend, as flow aloft
dampens into a westerly regime in behind the departing upper level
trough. Periodic energy moving east across Central TX may continue
some off and on showers and a few thunderstorms, but any flash
flood and severe weather threat will have ended. Weak upper
troughing and surface high pressure across the area will keep
sensible weather relatively quiet and cooler Sunday into Monday,
before the surface high shifts east.

Gradual low level moisture return will occur Monday night, ahead
of another shortwave trough aloft and associated cold front
arriving on Tuesday. Tuesday should be our next good, but brief
shot for showers and storms, though right now the thermodynamic
environment is too unknown and currently not looking overly
unstable for any severe weather. A cooler and brisk day Wednesday.
Shortwave ridging aloft and returning southerly surface winds the
end of the week will bring more seasonal late May warmth back to
the area. Rain chances look close to nil as well.



Dallas-Ft. Worth    68  81  59  82  62 /  70  50  30  10   5
Waco                70  83  61  82  63 /  60  60  60  20  20
Paris               68  79  56  80  58 /  70  60  30   5   0
Denton              65  78  55  82  58 /  70  40  20   5   5
McKinney            68  80  57  82  59 /  70  50  30   5   5
Dallas              70  82  61  83  63 /  70  50  40  10  10
Terrell             70  82  60  82  61 /  70  60  50  10  10
Corsicana           70  83  61  81  63 /  60  60  60  20  10
Temple              70  84  61  81  63 /  50  60  60  30  20
Mineral Wells       64  77  55  82  58 /  80  30  20   5  10



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