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

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FXUS64 KFWD 211157 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
657 AM CDT Sat Jul 21 2018


.AVIATION...
/12Z TAFs/

Only concerns the next 30 hours will be timing of wind direction
changes diurnally, then how wind fields reacts with the approach
of a weak cold front at the DFW terminals right before 12Z Sunday.
Otherwise, VFR conditions expected with occasional scattered-
broken cirrostratus left over from convective anvil debris moving
south across the Red River valley.

A strong mid-upper level high over West Texas and New Mexico will
persist and strengthen across North and Central Texas through
Sunday morning. Record setting heat will continue as well with
highs around 108-111 degrees today. Broken high clouds will have
little impact on both the heat and aviation services today into
tonight. Southwest winds 10-15 knots early today will back around
to the south AOB 10 knots by 00z Sunday. A weak cold front will
approach DFW terminals from the north-northeast after 06z Sunday.
Winds just ahead of this boundary will veer around to the west or
possibly become variable around 5 knots before 12z Sunday.

Confidence on where the weak cold front lays up early Sunday
morning, or whether a true FROPA occurs at DFW terminals is low due
to the lack of upper support. Confidence on the front should
improve as we move through the day and into tonight.

05/

&&


.SHORT TERM... /Issued 341 AM CDT Sat Jul 21 2018/
/Today and Tonight/

What else is there to say? Extremely hot once again today, possibly
hotter(if that`s possible) especially north of I-20 and west of
I-35/35W. The reason will be that just ahead of a weak low level
front across Central OK and the I-40 corridor will be an east-west
oriented surface-850mb thermal ridge with veered low level flow
from the southwest. 850mb temps between 28-32 deg/C will be
anchored right across the Red River Valley and affecting areas
between I-40 in Oklahoma and I-20 here in North Texas. Yesterday
concluded with DFW having set records 3 consecutive days, while
Waco was on 4 consecutive days. The record streak `should` continue
today (Records: DFW 107F in 2012 and Waco 105F in 1974), however
expansive cirrus from decaying storms across Northern Oklahoma
will spill southeastward across the Red River Valley and could
impede stronger insolation after sunrise this morning. The thicker
cirrus or cirrostratus lingering over our northeast counties
today may hold high temperatures down a few degrees lower than
areas further west of I-35/35E, where stronger subsidence from a
595-597 decameter upper high center is expected.

Thus the very hot, once again record-breaking forecast for today.
The hottest readings today should be from DFW and point north
through west, where readings from 109-112 degrees will be common.
Further east and north of I-20, I will advertise 107-109 degrees
due to an expected and at times, broken high cirrus canopy through
early or possibly mid afternoon. At these temperatures, I seriously
doubt you`ll notice much difference between a few degrees in this
oppressively hot environment. Areas south of I-20 will be a few
degrees cooler at 850mb, but see more insolation and will keep a
persistent forecast of 103-108 degrees across Central Texas.
Yesterday`s 00z FWD sounding was one of the hottest and dry
soundings I`ve personally seen since the Summers of 2011 and 2012,
thus, there`s zero chances I feel we see any isolated convection
in our CWA, even our northeast counties. As for heat index values,
strong mixing outside of the far eastern counties into the 50s
this afternoon should keep values from getting much above ambient
high temperatures this afternoon, which in themselves are beyond
oppressive.

Once again, several small grass fires cropped up across the area,
especially south of the I-20/30 corridors into Central Texas on
Friday. Looking at Energy Release Component(ERC) values and
percentiles, all but areas across our far southeast counties have
combustible small vegetation and grasses as the extremely hot
conditions stress out these fuels. These heat-stressed fuels will
combine with the very hot temperatures, low afternoon humidity at
or below 20 percent, and southwest winds 10 to 15 mph to create an
elevated grass fire danger. I will issue yet another Grass Fire
Danger Statement for all but Milam, Robertson, Leon, Freestone,
and Anderson counties for this elevated threat. Like in previous
days, the threat should wane with rising humidity values by sunset
and after this coming evening.

05/

&&

.LONG TERM... /Issued 341 AM CDT Sat Jul 21 2018/
/Sunday Onward/

The exceptional heat wave will continue on Sunday, although it
may be a few degrees cooler than Saturday across parts of North
Texas due to the presence of a weak front/trough. This boundary
should be located through our northeastern zones throughout the
day, with very weak cold advection via northeast winds behind it.
The thermal ridge axis will shift a bit to the south and west,
with 850mb temperatures slightly cooler than Saturday. With these
considerations in mind, our northeast zones may struggle to reach
103-105 depending on the effects of the weak front. However,
areas to the south should still experience southwest winds and
will be capable of climbing to 105-100F once again. Will keep the
Excessive Heat Warning for the entire area through Sunday for now.

On Monday, the aforementioned boundary will sink a bit farther
southwestward and the upper ridge will begin to retreat to the
west. These factors should contribute to slightly lower
temperatures, but areas along/south of I-20 will likely still meet
Excessive Heat Warning criteria. Our northern and eastern
counties however, should fall below, and may only require a Heat
Advisory or possibly no product at all depending on how much
cooler the air is on the northern side of the boundary. Due to the
uncertainty in where these cutoffs will occur, have not yet
extended any heat headlines into Monday, but this will need to be
evaluated in subsequent forecasts.

With the upper ridge moving west of the region, this will open
the door for a couple disturbances to pivot through in northerly
flow aloft. This should drive a stronger push of cooler air
through the region late Monday and into Tuesday. These
disturbances may be sufficient to generate a few showers or
storms, especially when aided by low-level convergence in the
vicinity in the boundary. Have included low PoPs for Monday
evening through Tuesday, but coverage will be minimal. There
would be some concern for downburst winds with any activity (even
showers) as convection would be very high-based (10 kft or more)
with very dry air below. Peak times for convective chances will be
Monday evening and again Tuesday afternoon with diurnal heating.
Otherwise, Tuesday should be noticeably cooler with the front
having passed through, although temperatures will still be above
normal with highs in the mid 90s to low 100s. Most of the area may
be able to get by without a heat product for the first time in
several days, but a few spots across Central Texas may continue
flirting with 105F heat indices.

For the second half of the week, the pattern will gradually become
less amplified with the upper ridge axis beginning to nudge back
into the area from the west. This should keep a a more seasonable
heat around with highs hovering near 100F and heat indices a
couple degrees higher. Rain chances should stay off to the north
and east of the area where the influence of the ridge is weaker.
There are some indications that the ridge may break down further
next weekend allowing another front and some rain chances to
return in the day 7-10 time period, but confidence is low as
expected that far into the forecast.

-Stalley

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth   110  83 109  82 105 /   0   0   0   0   5
Waco               109  78 110  80 109 /   0   0   0   0   5
Paris              107  78 102  77  98 /   0   0   0   5   5
Denton             111  80 109  78 104 /   0   0   0   0   5
McKinney           108  79 106  78 102 /   0   0   0   0   5
Dallas             110  85 109  84 106 /   0   0   0   0   5
Terrell            109  80 108  80 102 /   0   0   0   0   5
Corsicana          107  79 108  79 107 /   0   0   0   0   5
Temple             106  76 108  78 108 /   0   0   0   0   5
Mineral Wells      111  78 109  77 108 /   0   0   0   0   0

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 7 PM CDT Sunday for TXZ091>095-
100>107-115>123-129>135-141>148-156>162-174-175.

&&

$$

05/26


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