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Area forecast discussion
National Weather Service Fort Worth Texas
309 PM CDT Sat Jul 22 2017

Short term...
/this afternoon and tonight.../
isolated thunderstorms have popped up in an area of strong
insolation where temperatures have already hit 100, and have added
isolated thunder roughly along and west of a Bowie-Bridgeport-
Cisco line for the remainder of the afternoon. Subsidence from the
ridge aloft should shut off convection by sunset. This should
also hold true for seabreeze convection across the southeast
counties, where pops will drop below 20 after sunset. Otherwise,
hot and humid weather will persist this afternoon, particularly
along and east of the Interstate 35 corridor where heat indices
are exceeding 105 and a heat advisory remains in effect. Warm and
muggy conditions will persist tonight with low temperatures
generally in the 75 to 80 degree range.



Long term...
/Sunday through Saturday.../

An interesting and somewhat tricky forecast scenario is expected
to play out on Sunday across north and central Texas as several
weaknesses in the mid-level flow impinge upon the region. During
the morning hours, a relative Theta-E Max looks to set up roughly
along and just west of the I-35 corridor. At the same time, modest
isentropic upglide is forecast to materialize somewhere near the
310 k Theta surface. Point soundings reveal saturation occurring
here (the 310 k Theta surface should correspond roughly with the
700 mb level), and we even see some evidence of moist absolutely
unstable layers (mauls) materializing in forecast soundings. This
lends some degree of confidence that enough mid-level instability
and lift will be present to spark off a few showers/isolated
thunderstorms Sunday morning roughly west of a Gainesville to
Goldthwaite line.

Additional moisture will slosh westward on Sunday as well, with
pwats forecast to climb into the 1.75-2 inch range. As a result,
surface dewpoints may be a bit more hesitant to mix out during the
afternoon, and are expected to remain in the lower to middle 70s
along and east of the I-35 corridor. High temperatures are
somewhat of a wildcard in this forecast, as the rejuvenated
moisture should help spark off additional storms with the peak
heating of the day, and any morning activity may shed increased
mid-level cloud cover across the region. That said, we see enough
a a signal for heat index values climbing into the 105-108 degree
range to warrant extending the heat advisory through 7 PM on
Sunday for locations east of a Bowie to Killeen line.

The other story will be slightly better shower and thunderstorm
chances expanding across the entire region during the afternoon,
(mainly after 4 pm) with the greatest chances across our
southeastern-most counties. With such a moist airmass in place
and mean cloud-bearing flow of less than 5 kts, some locally
heavy rainfall will be possible. In addition, temperatures in the
upper 90s, dcape values in excess of 1000 j/kg, and low-level
Theta-E deficits of 25-35 k all spell a potential for a
(localized) damaging downburst wind threat with the most robust

Much of the daytime activity should begin to wane during the
evening, but we'll maintain low storm chances across the northern
half of the County Warning Area through Sunday night as convection firing across
Oklahoma may drift south of the Red River. Very weak low-level
wind fields mean any activity will be disorganized and should not
pose a severe weather risk. Any convectively-induced outflows may
then provide an additional focus for another round of showers and
storms on Monday before mid-level ridging gradually begins to
reassert itself Tuesday and beyond.

High temperatures and heat index values will once again begin to
increase as mid-level heights rise. Localized spots across central
Texas may begin to flirt with heat advisory criteria as early as
Tuesday afternoon, but more widespread and oppressive heat is
forecast to overspread the eastern 2/3rds of the region by the end
of the week. While uncertain at this time, it's possible that some
locations may even test excessive heat warning criteria (heat
index values of at least 110 degrees) into next weekend. Perhaps
we can find some limited consolation in the potential for some
shower/storm chances by Sunday.



Aviation... /issued 1244 PM CDT Sat Jul 22 2017/
subsidence provided by a broad ridge aloft should maintain the
quiet weather pattern for another day. An isolated storm will be
possible late this afternoon near the western dfw tracon boundary
where the hottest surface temperatures are forecast, but it
appears any of this activity would remain west of north/central
Texas taf sites. Otherwise, scattered convection can be expected well
southeast of the area along the Texas & la coastal areas.

A swath of Gulf moisture will push in from the east overnight and
Sunday around the north side of the Gulf Coast upper low, with
pwats increasing from 1.5 to near 2 inches by this time tomorrow.
This should aid in scattered thunderstorm development during peak
heating hours Sunday afternoon as diurnal instability increases.
In addition, a weak upper level disturbance is progged to drop
southeast through the Southern Plains, perhaps weakening the ridge
overhead. Though not a definite, confidence at this time is high
enough to include thunderstorms in the vicinity in the extended dfw taf. Otherwise,
conditions will remain VFR outside of any convection.



Preliminary point temps/pops...
Dallas-ft. Worth 80 99 80 98 80 / 10 30 20 20 10
Waco 77 99 77 99 77 / 10 30 20 10 10
Paris 75 95 75 94 75 / 5 30 20 30 20
Denton 78 99 78 98 77 / 10 20 20 20 20
McKinney 77 97 77 96 77 / 10 30 20 30 20
Dallas 81 99 80 98 80 / 10 30 20 20 10
Terrell 76 96 76 97 75 / 10 30 20 20 10
Corsicana 76 95 77 97 76 / 10 30 20 20 10
Temple 76 99 75 100 75 / 10 30 20 10 5
Mineral Wells 75 98 75 98 75 / 5 20 20 20 10


Forward watches/warnings/advisories...
heat advisory until 7 PM CDT Sunday for txz091>095-102>107-

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