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

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000
FXUS64 KFWD 131758
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1258 PM CDT Sun Aug 13 2017


.AVIATION...
Main aviation concerns lie within the first 6 hours of the TAF
period with lingering MVFR cigs and convective potential through
this afternoon. Scattered showers fueled by ascent from warm
advection continue to stream eastward along a stalled frontal
zone. Lingering MVFR stratus continues to affect DFW Metroplex
terminals intermittently with abundant low-level moisture still in
place. In the next few hours, isolated to scattered thunderstorms
are expected to develop near or just south of the I-20 corridor
with abundant moisture and moderate elevated instability
positioned near the frontal zone. Have included a few hours of
VCTS with low confidence in placement of the more robust
convection. Any storms that manage to develop should dissipate by
early evening. Waco is still generally expected to remain rain-
free through the period and have continued a dry TAF at this time,
although can`t rule out a rain shower late this afternoon.

Overnight, a complex of storms is expected to develop in the TX
Panhandle region and move eastward, possibly affecting part of
North TX in the process. Have maintained a mention of VCSH for
early Monday morning at DFW Metroplex sites when a few stray
showers could affect the area. There is a low potential for some
MVFR cigs at all TAF sites Monday morning, but the chance is too
low to include in the TAFs for now.

-Stalley

&&


.UPDATE... /Issued 1105 AM CDT Sun Aug 13 2017/
Quick update this morning mainly to account for trends in
temperatures and cloud cover. Have lowered temperatures a bit
across North Texas with clouds expected to hold through the
majority of the afternoon. However, if there are a couple hours of
clearing during peak heating,temperatures could still quickly
climb into the 90s. Clear skies across Central Texas have already
allowed temperatures to climb into the upper 80s as of 11am and
upper 90s are still expected this afternoon. Ascent along the
stalled frontal zone near I-20 is supporting scattered showers and
a few thunderstorms which will continue throughout the day. This
activity will be substantially less robust than overnight
convection, and additional widespread heavy rain is unlikely.

Products for this update have already been sent.

-Stalley

&&

.DISCUSSION... /Issued 436 AM CDT Sun Aug 13 2017/
With the westerlies draped across North Texas, the mid-level flow
has been remarkably potent for August. (The 00Z RAOB from FWD
sampled 40-45kts 500-400mb.) While this steering flow has
maintained progressive cell motion, it has also promoted training.
The passing shortwave responsible for the activity helped to
induce low-level inflow of 30kts, the resulting moisture flux
further enhancing rainfall amounts. Within the flash flood watch
area, a handful of locations have exceeded 3 inches of rainfall so
far. Through 4 AM, Commerce (Hunt County) had tallied 4.87".
Flooding concerns will continue through daybreak, but with the
low-level winds above the nocturnal boundary layer already
veering, the activity from Sherman/Denison to Sulphur Springs
will likely be the last of this intensity. The renewed activity in
our northwest zones shows the impulse aloft isn`t done yet, but
while the depth of this convection is sufficient for thunder, the
warmer cloud tops are evidence that the lapse rates aloft are
diminishing. Even without the rates of earlier activity, this
complex will track over our soggy northeast zones, and any
additional rainfall will only worsen or re-aggravate flooding
issues.

As the disturbance finally passes to the east this morning, a
lull in the precipitation will follow. The heavy rain in our
northeast zones will likely result in convectively induced
vorticity that may also be evident in the surface wind field as
cyclogenesis. While this feature will move away from us today, it
will likely tug our persistent surface boundary north to near the
Red River. It may even disrupt the surface wind field enough to
eliminate the boundary entirely. However, with the sun emerging in
our southern zones, heating a relatively untapped boundary layer
that will advect slowly northward, there should still be an
effective thermal discontinuity that will serve as the focus for
thunderstorm development this afternoon. Although our forecast has
a wide band of chance PoPs, the axis of activity this afternoon
will likely be pretty narrow, perhaps in vicinity of the I-20
corridor. Rich Gulf moisture should be sufficient for updrafts
supportive of thunder, but the milder boundary layer and the lack
of upper support should greatly limit the severe potential. While
the activity may look organized in a quasi-linear fashion and
there will remain decent mid-level flow, these cells will behave
more like typical August showers/storms than what we saw on
Saturday.

The next shortwave will emerge from the Rockies this afternoon,
likely initiating another MCS on the high terrain of the
Panhandles and western Kansas. With a renewed low-level jet, the
activity will likely survive the night, potentially arriving in
North Texas for the Monday morning commute. Steepening lapse rates
aloft will maintain thunder potential, but this complex should be
of lesser intensity than Saturday night`s activity.

Shortwave ridging in the wake of Monday`s shortwave would normally
help the subtropical ridging to re-establish itself, but the
extent of the precipitation preceding it will likely keep this
from happening right away. Longwave troughing across the western
states will keep West Texas in southwest flow through mid-week.
Periodic impulses and resulting storm complexes may impact our
western/northwestern zones (most notably Tuesday night), but the
remainder of our CWA will become increasingly influenced by
ridging aloft backbuilding from the east. As a result, the heat
will steadily return. By Tuesday, heat index values may approach
105 in some areas. A heat advisory will likely be needed by
Wednesday with the August heat prevailing into next weekend.

25

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    88  76  96  78  97 /  50  20  20   5   5
Waco                97  78  98  78  99 /  20  10   5   5   5
Paris               83  73  89  74  93 /  80  30  40  20  10
Denton              86  76  94  77  96 /  50  30  20  10  10
McKinney            86  75  93  77  96 /  60  30  20  10  10
Dallas              89  77  95  79  97 /  50  20  20   5   5
Terrell             89  75  94  78  96 /  60  20  20   5   5
Corsicana           94  76  96  77  97 /  40  10  10   5   5
Temple              98  77  98  77  99 /  10  10   5   5   5
Mineral Wells       87  75  96  76  97 /  50  20  10  10   5

&&

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

$$

26/91



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