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

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067
FXUS64 KFWD 282109
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
409 PM CDT Fri Apr 28 2017

.DISCUSSION...

Water vapor imagery shows a large upper trough over the western
U.S. this afternoon. This system is expected to move east through
tomorrow night bringing increasing chances for showers and
thunderstorms to North Texas along with an increased threat for
severe weather.

At the surface this afternoon, an area of low pressure is located
near Big Spring with a dryline extending southward from there. A
warm front is located just north of the Red River. South of the
warm front, the atmosphere has become quite unstable with surface
dewpoints now in the upper 60s and lower 70s across North Texas.
In the presence of very steep lapse rates associated with a deep
elevated mixed layer, this high near-surface moisture results in
instability values between 2500-3500 J/kg. While this is an
impressive amount of instability, it remains mostly capped, as
indicated by unimpressive visible satellite data and visual
observations of the cumulus field. This strong inhibition should
remain in place through early evening resulting in little or no
chances for thunderstorms across North Texas.

By later this evening as stronger forcing for ascent spreads into
the Southern Plains from the approaching upper trough, low level
southerly flow will strengthen. A 50 kt low level jet will develop
and be centered right over North Texas with low level warm
advection maximized right near the Red River. The combination of
increasing ascent and the presence of the surface frontal boundary
should be sufficient to weaken the strong capping and allow deep
convection to develop. Most of this activity should be north of
the Red River across much of Oklahoma, however there will be low
chances for our Red River counties through late tonight. The
timing of this development would likely be 8-10 pm or so. Given
the amount of instability available, there would be a threat for
severe weather including very large hail and damaging winds. Low
level shear will also be sufficient to support a tornado threat,
although the better environment will be north of the Red River
closer to the actual frontal boundary.

A large area of thunderstorms are expected to be ongoing during
the overnight hours across Oklahoma and northwest Texas. These
storms will approach North Texas from the northwest in the form of
a weakening squall line as the stronger low level jet shifts to
the northeast. This ongoing convection is likely to move through
our western counties during the morning hours and may pose a
severe hail threat, so will have some higher PoPs through midday
across the western counties.

The evolution of the afternoon severe threat across North Texas on
Saturday will be somewhat dependent upon where any outflow
boundaries set up and the position of the synoptic cold front.
With the strong upper trough still to the west, it does appear
that much of North Texas will have time to destabilize by midday
with low level wind fields recovering behind any morning activity.
The main question for tomorrow is where exactly the new vigorous
convection develops along the cold front. Right now, it appears
that this will occur very near the I-35 corridor in the 1-3 pm
timeframe. Wind fields will be unidirectional by this time which
should help limit the tornado potential, but ample instability
will support a very large hail threat. The highest PoPs and best
severe weather threat will generally be along and east of I-35
through the evening hours with our eastern counties having the
most time to fully destabilize. The severe thunderstorms will move
east with the cold front and should clear our CWA during the late
evening hours.

The upper trough will actually not move through North Texas until
Saturday night and there will be sufficient moisture for continued
elevated convection across much of the region. In fact, PoPs may
actually be higher across the region Saturday night as the trough
moves through than with the deep convection along the front. There
will be a continued hail threat with this overnight activity.

Conditions improve across the region on Sunday with northwest
winds and clearing skies. Additional rain/storm chances arrive mid
week with another upper trough moving through the Plains.

Dunn

&&

.AVIATION...
/ISSUED 1251 PM CDT Fri Apr 28 2017/
VFR conditions will prevail through the evening with southerly
winds generally at 10-15 kt. Just some fair weather cumulus and
high cloud cover is anticipated, as a strong cap should hold
across the TRACON. Any convection that fires late this afternoon
or evening should stay well north/northwest where cap is weaker.

MVFR CIGs near 1500 ft will arrive around 7z/1am, but MOS/model
guidance looks too pessimistic with IFR forecasts. Winds may
increase slightly overnight to the 15-20kt range with higher
gusts. These strong winds and unseasonably warm temperatures
typically prevent IFR conditions. The MVFR CIGs should prevail
through the morning hours as moisture advection continues ahead
of a strong upper system and cold front. A strong cap will remain
in place through the morning hours, but the ample moisture and
weak lift below the cap may lead to very light showers.

For the extended DFW TAF, have included VCTS starting at 18z as
the strong lift begins to erode the cap. Generally favored the
faster timing in the high-res and convection allowing models so
the best window for thunderstorms looks to be around 18-21z/1pm-
4pm with the cold front passing through around mid afternoon.
Potential for scattered convection and storms may continue for a
couple hours in the wake of frontal passage. Given ample shear
and instability, some storms could be severe.

TR.92


&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    74  82  54  67  49 /  20  70  60  10   0
Waco                75  84  55  70  47 /  10  50  60  10   0
Paris               72  81  56  63  46 /  40  80 100  20   0
Denton              72  79  51  65  45 /  30  70  50  10   0
McKinney            73  82  53  65  46 /  30  80  70  10   0
Dallas              75  83  54  67  50 /  20  70  60  10   0
Terrell             74  83  54  67  47 /  20  80  90  10   0
Corsicana           75  84  55  69  49 /  10  70  80  10   0
Temple              74  85  56  71  48 /  10  40  60  10   0
Mineral Wells       70  78  47  67  44 /  30  40  50   5   0

&&

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

$$



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