Flash Flood Warning 43, NWS Fort Worth, TX

Area Forecast Discussion
National Weather Service Fort Worth TX
352 AM CDT Fri Aug 25 2017

.DISCUSSION...
Satellite imagery shows that the structure of Hurricane Harvey
continues to improve with concentric cirrus banding already
reaching the southern half of the CWA early this morning. RADAR
Mosaic indicates outer rain bands extending from the Texas Coastal
Bend to just south of the Upper Texas Coast. The system is still
progged to make landfall early Saturday along the Coastal Bend,
and it's future track will continue to be the primary focus for
this forecast.

Meanwhile, a tropical airmass is already in place based on the 2
inch PWAT analyzed on the 06Z sounding. Similar to last night,
nocturnal showers and a few embedded thunderstorms have popped up,
this time generally south of the I-20 corridor. We will need to
keep an eye on any training precipitation due to the potential of
heavy rain and localized flooding. For today, the higher POPs will
be across the western half of the region where weak forcing aloft
will be present, although isolated storms will still be possible
across the eastern counties.

After today, the focus will shift almost solely on Harvey, which will
already have begun to inundate the Mid Texas Coast with hurricane
conditions and South-Central Texas with torrential rains and
likely dangerous flooding. The main change with this forecast
package is to include a Flash Flood Watch across the southern tier
counties where outer bands will likely reach this weekend and
storm total precipitation values of 5-6 inches are forecast. These
counties will also experience breezy conditions this weekend but
at this time it appears that winds will remain below tropical
storm criteria.

The Flash Flood Watch will run from Saturday morning through
Sunday night, and it is likely to be extended at least temporally
and possibly spatially in future forecasts. The decision to not
extend the watch into next week is based on the continued
uncertainty in the exact track of Harvey beyond 72 hours. After
meandering in and around the coastal bend this weekend, the
official forecast track brings the system farther up the Texas
Coast, keeping it in Southeast Texas on day 5 (Tuesday). This
could keep the potential for heavy rain and flooding going into
next week across the southern CWA. However, the cone of
uncertainty becomes quite large by this time and the official
track could change. For now, the extended portion of the forecast
will lean close to persistence with the highest POPs across the
south. Otherwise, due to the extensive cloudcover and precip
chances, temperatures will remain below normal for this time of
year for the entire forecast.

30

&&

.AVIATION... /Issued 1230 AM CDT Fri Aug 25 2017/
/06Z TAFs/

Diurnally driven convection has blended nearly seamlessly into
nocturnal showers as gentle but very moist easterly upglide has
ensued again tonight across North and Central Texas. The coverage
and intensity will be less than the Wednesday night/Thursday
morning activity, which should limit the extent of any MVFR
ceilings. But with a nearly saturated boundary layer, lower
ceilings may need to be introduced toward daybreak, particularly
if the showers are more widespread than anticipated. The showers
will gradually taper off from south to north later this morning.

The rich tropical air mass will remain in place Friday afternoon,
but North Texas may be in area of subsidence between Harvey and
the troughing to our northwest. The boundary layer will
undoubtedly want to convect, but this inhibition should limit
coverage, and the TAFs will be free of precipitation after the
morning showers come to an end. The first outer rain band from
Harvey may invade Central Texas near the end of the current Waco
TAF. This will be reassessed with subsequent issuances, but the
only impacts would be rain and gusty winds on par with garden-
variety summertime convection.

25

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    88  74  88  72  88 /  40  20  30  30  20
Waco                90  74  85  72  83 /  40  30  60  50  40
Paris               86  70  87  70  86 /  20  10  20  20  20
Denton              86  71  88  70  88 /  40  20  20  20  20
McKinney            87  69  87  69  87 /  40  10  20  30  20
Dallas              89  75  88  73  88 /  40  20  30  30  20
Terrell             89  72  87  72  86 /  40  10  30  30  30
Corsicana           90  75  86  73  84 /  30  20  50  50  40
Temple              89  74  83  71  81 /  50  40  70  70  60
Mineral Wells       86  70  87  69  87 /  50  20  30  30  20

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from Saturday morning through Monday morning
for TXZ158-160-174-175.

&&

30/58

Hazardous Weather Outlook
National Weather Service Fort Worth TX
433 AM CDT Fri Aug 25 2017

TXZ091>095-100>107-115>123-129>135-141>148-156>162-174-175-261100-
Montague-Cooke-Grayson-Fannin-Lamar-Young-Jack-Wise-Denton-Collin-
Hunt-Delta-Hopkins-Stephens-Palo Pinto-Parker-Tarrant-Dallas-
Rockwall-Kaufman-Van Zandt-Rains-Eastland-Erath-Hood-Somervell-
Johnson-Ellis-Henderson-Comanche-Mills-Hamilton-Bosque-Hill-Navarro-
Freestone-Anderson-Lampasas-Coryell-Bell-McLennan-Falls-Limestone-
Leon-Milam-Robertson-
433 AM CDT Fri Aug 25 2017

This Hazardous Weather Outlook is for North and Central Texas.

.DAY ONE...Today and Tonight.
There is a chance of thunderstorms across all of North and Central
Texas today and mainly southwest of a Sherman to Terrell to Canton
line tonight. Severe weather is not expected but heavy rain may
produce localized flooding.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.
On Saturday and Sunday, there is a potential for widespread heavy
rainfall across parts of Central Texas as the outer reaches of
Hurricane Harvey begin to impact the region. While there is still
uncertainty on the exact track and timing of this system, heavy
rainfall south of a Goldthwaite to Waco to Palestine line may lead to
flash flooding during this time frame. In addition, strong winds
with some gusts to 35 mph will be possible.

Thunderstorm chances will shift to southeast of a Comanche to Sherman
line Monday and will be mainly along and east of I-35/I-35W Tuesday
through Thursday.

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected at this time.