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

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306
FXUS64 KFWD 230050 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
750 PM CDT Tue Aug 22 2017

.AVIATION...
/00Z TAFs/

The bulk of the region`s showers and thunderstorms today have been
confined to an early season cold front from West Texas into
Oklahoma. However, with little inhibition, a few disorganized
cells developed across North Texas at peak heating. With minimal
shear, these updrafts have struggled to survive for any length of
time, and the radar scope should be clear across the DFW TRACON
the remainder of the evening. But west/northbound traffic and
inbounds through the Bowie cornerpost will continue to have some
disruptions.

Although the storms associated with the boundary will diminish in
intensity overnight, some showers will accompany the front as it
reaches the Metroplex during the early morning hours Wednesday.
The advancing boundary will maintain some convection, but the
weak shear and marginal lapse rates aloft should limit the
incidence of thunder. These showers will continue through the
morning push.

The boundary should pass Waco mid to late morning at a time when
the nocturnal showers are on the wane. The main focus during the
afternoon hours will likely be to the south of the Waco terminal,
but it may be close enough to warrant inclusion in subsequent TAF
issuances. Deeper into the postfrontal air, the Metroplex
terminals should have a lull in activity Wednesday
afternoon/evening through Wednesday night.

Winds near the top of the frontal inversion will veer Wednesday
night, sending an upglide of moisture above the shallow
postfrontal layer. This bout of stratus is currently beyond the
extended portion of the DFW TAF but will likely need to be
included with the 06Z package.

25

&&

.SHORT TERM... /Issued 338 PM CDT Tue Aug 22 2017/
/This Afternoon through Wednesday/

A current surface analysis shows several mesoscale features we are
monitoring for the evening hours. First, the seabreeze is making
its way inland from the southeast Texas coast but will likely not
reach our southern counties this evening. However, a few isolated
showers have developed north of the boundary about a county south
of our border. It`s possible an isolated shower may occur in our
far southern row of counties but will keep a silent 10% in that
area through the evening hours. Second, an outflow boundary has
spent most of the day moving southwest across Arkansas, and is now
moving into southeast Oklahoma and southwest Arkansas. This
boundary continues to make steady progress southwest but will
likely stall this evening. However, will introduce a small chance
for convection in our far northeastern counties this evening in
case this outflow boundary does move into Northeast Texas.

The third feature of interest is a weak surface low in the
vicinity of Frederick Oklahoma. Some convection has developed
near this surface low where differential heating is occurring
outside of an earlier cloud deck. Convection has been developing
in our northwest counties and will likely continue to occur there
through the late afternoon evening hours. The environment is
unstable and uncapped, and the most likely threat would be strong
or near severe wind gusts.

Finally, a cold front continues to progress south through
Oklahoma and the Texas Panhandle. Convection is already developing
along this front across the Panhandle. The front and associated
convection are expected to approach the Red River late this
evening and/or near midnight. Highest rain chances overnight and
into Wednesday morning are along and north of Interstate 20.
Severe weather is not expected but gusty winds will be possible.
In addition, heavy rain will be possible and this may result in
some flooding problems along our Red River counties. At this
time, the current anticipation is any flooding problems would be
minor.

On Wednesday, rain chances are expected to shift south during the
day with the front. We anticipate rain will dissipate during the
morning hours with isolated to scattered afternoon convection
along and near the diffuse frontal boundary, mainly south of the
Interstate 20 corridor. Strong winds and lightning will be the
main hazard with any afternoon storms.

JLDunn

&&

.LONG TERM... /Issued 338 PM CDT Tue Aug 22 2017/
/Wednesday Night and Beyond/

The main focus of the extended forecast is any potential impact
from the remains of Tropical Storm Harvey, which is expected to
re-intensify in the western Gulf of Mexico in the next couple of
days. This system could bring widespread heavy rain and flooding
to parts of South and Central Texas over the upcoming weekend,
although there is still substantial uncertainty in the system`s
track and intensity. Otherwise, our area is expected to maintain
above normal rainfall chances and near- or below-normal
temperatures into next week.

Scattered showers and thunderstorms should be ongoing Wednesday
afternoon/evening, mostly along a stalled frontal zone draped through
Central Texas. Activity could continue overnight Wednesday into
Thursday morning as weak ascent prevails in vicinity of the front,
although coverage should be fairly sparse. Another flare-up
should occur Thursday afternoon via daytime heating and have
maintained broad-brushed 20-40% PoPs without knowing exactly where
convergent boundaries will be placed. Slightly cooler and drier
air will remain in place north of the front which will help hold
temperatures below normal, especially across North Texas. Chances
for scattered thunderstorms will continue on Friday as the front
remains positioned through the forecast area, although it should
begin losing its identity by this time.

Later on Friday, the focus shifts to the Harvey remnants which
will making landfall somewhere along the TX coast. The latest GFS,
ECMWF, and CMC are all in reasonably good agreement on tracking
this system northwestward into South TX and the Hill Country
region by Friday night/Saturday. However, caution should be used
when evaluating specific model details over the next day or two,
as models do not yet have a circulation center at initialization
time. Some substantial changes to the track/evolution should still
be expected in the next few days. That being said, confidence is
high that some locations in South/Central TX will receive too
much rain over the weekend which will result in flooding. For our
forecast area, generally the farther south your location, the
greater the rain chances/amounts are expected to be. Some of our
zones along/south of a Temple to Waco to Palestine line could see
multi-inch rainfall totals if current guidance is remotely
correct. The highest potential for rain right now appears to be
Saturday afternoon through Sunday when the circulation is progged
to approach the area, stall, and then move east as it becomes
picked up by mid-latitude westerlies within a deepening upper
trough. Rain chances begin to taper off by Monday as the system
should be departing to the east.

Of slightly lesser importance, there is a substantial bust
potential in the temperature forecast from Friday through Sunday
as it hinges on cloud cover associated with the approaching
tropical system. Have sided on cooler guidance especially across
the south where dense clouds and outer rain bands could be
located. Across North TX, if subsidence is strong and skies aren`t
as cloudy as expected, temperatures could rise well above my
current forecast.

To reiterate, regardless of Harvey`s exact track/circulation
position, the main focus for our forecast area should be the
potential for very heavy rain and possibly some flooding across
our Central TX counties. Folks should expect to see multiple
changes to the forecast in the coming days as new data becomes
available. We`ll need to wait a bit longer to assess the
potential for strong sustained winds in our southern counties, as
well as how favorable the environment may be for tropical cyclone
tornadoes.

-Stalley

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    79  91  74  88  72 /  50  50  30  20  20
Waco                74  96  75  91  72 /  10  40  30  40  30
Paris               73  87  68  85  66 /  50  40  20  10   5
Denton              74  90  72  87  69 /  60  50  20  20  10
McKinney            71  89  70  87  68 /  50  50  20  20  10
Dallas              80  91  74  88  72 /  50  50  30  20  20
Terrell             73  91  72  88  70 /  40  50  30  20  10
Corsicana           76  94  74  89  72 /  20  40  30  30  20
Temple              74  96  74  92  73 /  10  40  30  40  40
Mineral Wells       74  87  70  87  69 /  50  50  30  30  20

&&

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

$$

25/05



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