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

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FXUS64 KFWD 131223 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
723 AM CDT Sun Aug 13 2017


.AVIATION...
/12Z TAFs/

Concerns: Continued convective potential at the DFW airports. IFR
and MVFR cigs this morning and possibly Monday morning.

DFW Airports: Isolated showers continue to develop and move
across the Metroplex this morning. Model guidance is split on
convective trends for the remainder of the day and how the
atmosphere will recover later today. With new development out west
from Abilene to Lubbock, some high resolution guidance develops
this into another cluster that moves across the region later this
morning. Other guidance redevelops storms along the weak frontal
boundary this afternoon. Confidence in trends for the remainder of
the day remain low and significant changes may be made with
scheduled amendments. For now, will keep a VCSH mention through
15Z with VCTS from 21-02Z. Overnight, additional showers may
develop as the low level jet increases with the retreating
boundary/front. A complex of storms will approach the region from
the northwest and may bring a chance for additional showers and
storms after daybreak.

IFR and MVFR cigs are in place across much of North Texas, mainly
impacting KAFW and locations outside the remaining DFW airports.
Will keep a TEMPO for BKN010 through 15Z, but then expect
conditions to improve. With isentropic lift across the region
again tonight as the low level jet increases to 30 kts, additional
MVFR cigs are possible.

Waco Airport: Light rain may occasionally cross KACT this
morning, and there is a low chance convection may occur near KACT
this afternoon, but confidence is too low to mention in the TAF
at this time. Otherwise, VFR conditions are expected today with
southwest winds this morning becoming more southeasterly this
evening. Some MVFR cigs are possible late tonight and Monday
morning as warm air advection increases with an increasing low
level jet of 30 kts.

JLDunn

&&


.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    92  76  96  78  97 /  50  30  20   5   5
Waco                98  78  98  78  99 /  20  10   5   5   5
Paris               83  73  89  74  93 /  80  30  40  20  10
Denton              90  76  94  77  96 /  50  30  20  10  10
McKinney            89  75  93  77  96 /  60  30  20  10  10
Dallas              93  77  95  79  97 /  50  30  20   5   5
Terrell             92  75  94  78  96 /  60  30  20   5   5
Corsicana           94  76  96  77  97 /  40  20  10   5   5
Temple              99  77  98  77  99 /  10  10   5   5   5
Mineral Wells       92  75  96  76  97 /  30  30  10  10   5

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until 7 AM CDT this morning for TXZ092>095-
105>107.

&&

$$

82/25



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