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

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806
FXUS64 KFWD 241731 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1231 PM CDT SAT SEP 24 2016

.AVIATION...
Showers and thunderstorms are gradually expanding in coverage
early this afternoon. Coverage is still expected to remain just
isolated to scattered, but on-and-off impacts from thunder are
expected at all of our TAF sites into the mid-afternoon hours. Any
cells will bring with them gusty and chaotic winds and brief MVFR
cig/vis reductions.

The evolution of convective potential late tonight and Sunday
morning remains a bit unclear. Some high-resolution guidance has
aggressively driven an outflow boundary into the Metroplex sites
as early as 06-08Z, bringing with it a brief northwest wind shift
and scattered thunderstorms. However, the environment to our north
and west does not appear to strongly favor the development of a
surging outflow tonight. As a result, I`ve continued to side with
the slower guidance, and will bring VCTS into the Metroplex sites
after 11Z. This timing may be just quick enough to disrupt the
nocturnal development of low clouds in the Metroplex, but an even
slower progression would translate into an increased risk for MVFR
cigs early Sunday morning.

I`ve also attempted to highlight the most likely timing for
thunder in the Metroplex on Sunday. As profiles moisten, activity
may become more showery in nature late Sunday morning.
Thunderstorms may once again re-develop during the mid-afternoon
hours with just a bit of filtered heating. In the DFW extended
TAF, a north windshift will occur with the passage of the actual
cold front around 21Z.

At Waco: after thunderstorms diminish later this afternoon and
evening, MVFR cigs should once again move north late tonight into
Sunday morning. I anticipate the better thunder chances holding
off until towards the end of the valid Waco TAF cycle.

Carlaw

&&

.UPDATE...
Small showers are already developing in Central Texas this
morning, creeping north into North Texas. No lightning has been
observed yet but the potential for lightning will increase this
afternoon as temperatures continue to rise and the instability
increases. Forecast soundings for this afternoon show a mostly
uncapped atmosphere with around 2000 J/kg of CAPE. However, deep
layer shear values are less than 15 kts so expect mostly general
thunderstorms, but a few storms could become strong producing
gusty downburst winds. Have increased PoPs for this afternoon
south of Interstate 20 where the best instability is expected.
The instability and temperatures may be limited by cloud cover but
enough breaks in the clouds should allow for sufficient heating
of temperatures into the lower 90s which will support convective
development.

Our attention throughout the day will also remain on convective
trends to our west. Showers and thunderstorms are increasing in
coverage across the Texas Panhandle and West Texas where lift from
a trough over the intermountain west is occurring. Previous runs
of the HRRR this morning have consistently been advancing this
area of rain east and into North Texas by around 7 pm this
evening. The HRRR has support from the 00Z WRF-ARW but this
solution seems a little far fetched as the mean steering flow is
from the south and southwest and the environment does not appear
conducive for this area to develop a large outflow boundary that
would push the rain to the east this afternoon. This area of rain
will likely advance east later today (this evening) as another
shortwave moves north out of Mexico, increasing the lift across
the state. For the time being, maintained 40 PoPs in the
northwestern counties through 7 pm but then increased PoPs in this
area in the evening hours for the possibility of rain reaching
those counties before midnight this evening. As the overnight
period continues, it appears this large area of rain will weaken
but will continue to see redevelopment of scattered rain over
roughly the western third to half of the CWA, with the best rain
chances still on Sunday.

For the remainder of the forecast, made minor adjustments to high
temperatures based on latest observations. Increased our
northwestern counties closer to 90 degrees where temperatures are
already in the lower 80s and cloud cover will likely remain
scattered to broken through the day.

JLDunn

&&

.PREV DISCUSSION... /ISSUED 437 AM CDT SAT SEP 24 2016/
Although less widespread than during the daylight hours Friday,
showers and thunderstorms continue along a cold front within the
Texas Panhandle. With weak advection behind the boundary and the
mean flow nearly parallel to it, the front will make little
additional progress today. However, as the next surge of lift
currently emerging from Mexico and moving northward across the
Trans Pecos spreads over the warming and destabilizing daytime
boundary layer, the activity will expand in areal coverage. By
midday, showers and storms will likely stretch along the front
from Big Bend through the eastern Texas Panhandle northward into
Kansas. Despite profiles that favor training, the activity will
likely bleed eastward as outflow heads into richer moisture. Even
then, it may take until nightfall for these convective elements to
reach the northwestern edge of our CWA. In the meantime, with the
subsidence that has dominated the region in recent days waning,
scattered showers and storms may develop across North and Central
Texas this afternoon, well ahead of the approaching MCS. This
diurnally driven activity will be largely disorganized, and
lightning interrupting outdoor activities will be the primary
concern today.

As the tail end of a longwave trough begins cutting off tonight
over the Gadsden Purchase, the main forcing will remain to our
west. Some of the ongoing convection this evening may persist into
the overnight hours, impacting areas mainly west of the I-35
corridor. The heavy rain threat should remain confined to the next
impulse that will affect the Big Bend and Permian Basin early
Sunday. Although the best forcing will remain well to our west,
the West Texas activity will make a more forceful surge eastward
during the daylight hours Sunday. In addition, more widespread
development will likely occur across North and Central Texas ahead
of the main complex, perhaps as a continuation of any remnant
nocturnal activity. The hazard grids will confine the flooding
potential to areas generally west of a line from Bowie to Granbury
to Goldthwaite.

A cold front will dive south through West Texas during the day
Sunday. The extent of the showers and thunderstorms may give a
false impression of its progress, but the boundary should
eventually surge through North and Central Texas Sunday night. As
drier air filters into the region, the PoPs will steadily decrease
from north to south Monday. If the clouds hang in on Monday,
daytime temperatures may peak in the 70s with breezy north winds.
The rain chances will come to an end Tuesday as upper ridging
begins to re-establish itself. However, this does not mean a
return to summer heat. Seasonal daytime temperatures in the 80s
will feel remarkably pleasant with low humidity. The Gulf will
remain closed, keeping the 70-something (and even the
60-something) dew points at bay into next weekend.

25



&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    91  74  85  66  78 /  30  30  60  60  50
Waco                92  73  87  67  78 /  40  20  60  60  60
Paris               91  71  88  67  80 /  30  20  40  40  20
Denton              90  72  83  65  76 /  30  40  70  60  50
McKinney            91  72  86  67  79 /  30  30  50  50  40
Dallas              92  74  86  67  77 /  30  30  60  60  40
Terrell             91  74  89  68  80 /  30  20  50  50  40
Corsicana           91  73  88  70  80 /  30  20  60  60  50
Temple              91  72  86  67  79 /  40  20  70  60  60
Mineral Wells       89  71  81  63  74 /  30  50  80  70  50

&&

.FWD Watches/Warnings/Advisories...
None.
&&

$$

90/82



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