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

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FXUS64 KFWD 171917 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
217 PM CDT Thu Aug 17 2017


.AVIATION...
The thunderstorm complex that moved through the TAF sites this
morning temporarily stabilized the atmosphere. However, we are
getting enough heating for isolated showers to pop up. Have
included VCTS for the 19-21z period at KDAL and KGKY and
will be prepared to update the other Metroplex TAF if it looks
like there will be additional development. The MVFR ceilings have
mostly given way to VFR, and outside of thunderstorms, VFR
conditions are expected to prevail. Winds will be south to
southeast at around 10 knots.

At Waco...Scattered showers and thunderstorms are possible
this afternoon into this evening. Have kept VCSH through
21z with VCTS for the 21z-02z period.  Otherwise, expect
VFR conditions with southeast to south winds around
10 knots.

58

&&


.DISCUSSION... /Issued 353 AM CDT Thu Aug 17 2017/
A complex of storms has successfully crossed the Red River this
morning and continues moving south and southeast along its well
defined outflow boundary. While new convection continues to
develop along the leading edge outflow, a broader swath of
moderate to brief heavy rain continues behind the outflow as a
30-40 kt low level jet provides lift over the boundary. This
system will continue to progress across North Texas this morning,
but will likely slow down and dissipate before midday as the low
level jet weakens and veers to the southwest. Ahead of the
complex, additional showers and storms are possible this morning
associated with warm air advection with the low level jet.

So far, winds of 20-30 mph have been occurring with the leading
edge outflow and storms. A few strong storms with winds near 40
mph may be possible this morning, and an isolated severe storm
cannot be completely ruled out, but overall, severe storms are
not expected. Gusty winds, lightning strikes, and brief heavy
rainfall will be the main hazards with the morning storms. Minor
flooding may occur, especially in counties near the Red River
where moderate to heavy rainfall falling on still saturated soils
may have trouble running off.

The remnants of the complex are expected to leave a diffuse
boundary across the region. Where exactly this boundary stalls is
yet to be determined, but much of the hi-res guidance appears to
suggest a location near the I-20 corridor, give or take about 40
miles to the south or north. New convection should develop along
this boundary this afternoon and will keep fairly high PoPs across
the middle part of the CWA as a result. Forecast soundings
indicate an uncapped environment this afternoon characterized by
modest instability around 2000 J/kg but with weak lapse rates and
low deep layer shear near 10 kts. This type of environment
usually signifies pulse-type convection very common in the summer
where the main threats will be lightning, downbursts, and brief
downpours due to a slow movement.

Rain chances today are lowest across our far southern counties,
and it is these counties that have the highest threat for
dangerous heat conditions. A Heat Advisory has been issued along
and south of a line from Killeen to Palestine where heat indices
of 105 to 110 degrees are possible. Dewpoints will mix out later
this afternoon, but the highest heat index values are expected
between the hours of noon and 4 pm, before maximum mixing occurs.
With likely a stalled outflow boundary to the north of these
counties, light wind and pooling of moisture may occur, resulting
in the dangerous heat indices. There are 2 caveats: 1) cloud
cover may hang around longer than expected and 2) the boundary
could push farther south than expected with rain this afternoon
near or in the Advisory area. However, based on the latest
expected trends and calculations, did not want to delay
advertising the potential for high heat index values in that area
of Central and East Texas.

The upper level ridge will continue to build into the region over
the weekend and temperatures will climb a little more as a result.
Isolated to scattered afternoon convection is possible across
mainly the northern half of the region on Friday, and then drier
conditions are expected. We will have to monitor for MCS activity
the next few nights, and the latest guidance suggests another MCS
may graze our northern counties Friday night/Saturday morning. The
heat will increase over the weekend as heat index values rise to
near Advisory criteria across most of the area along and east of
Interstate 35. Some showers or storms may be possible in our
southern counties by the middle of the week as an upper level
disturbance retrogrades west across the Gulf of Mexico and into
South Texas.

JLDunn

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    78  98  79  98  79 /  20  20   5  10   5
Waco                78 100  77 100  77 /  40  10   5  10   0
Paris               74  93  74  94  74 /  20  40  20  20  10
Denton              76  98  76  97  76 /  20  20  10  10   5
McKinney            76  96  76  96  76 /  20  30  10  20  10
Dallas              78  97  79  97  79 /  20  20   5  10   5
Terrell             75  96  75  97  75 /  30  20   5  20   5
Corsicana           77  97  77  98  77 /  40  20   5  10   5
Temple              76  99  76 100  76 /  30   5   5  10   0
Mineral Wells       75  97  74  98  74 /  20  20   5  10   5

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 6 PM CDT this evening for TXZ158-160-161-174-
175.

&&

$$

58/05



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