Special Weather Statement, NWS Fort Worth, TX

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
646 PM CDT Wed Jun 20 2018

.AVIATION...
/00z TAFs/

The main concern this evening revolves around the convective
potential at the Metroplex TAF sites. Thunderstorms are ongoing
just north of the Red River early this evening near a cold front
and these will continue to gradually sink southward over the next
few hours. Visible satellite imagery also reveals the Cu field
just north and west of the Metroplex is becoming a bit more
agitated, with several convective initiation attempts noted over
the last hour. The currently-ascending 00z RAOB sampled some
fairly warm air around 700-750 mb, but the effects of a nearby
shortwave may be sufficient to erode this over the next hour or
two. As a result, we've elected to TEMPO TSRA at the Metroplex
airports (02-04z at DFW, DAL, AFW, and FTW, and 03-05z at GKY). A
brief north wind shift will be possible as convection passes, but
conditions should rapidly improve after 05z. At Waco,
precipitation chances appear too low to warrant an explicit
mention through the TAF period.

Overnight, there are signals that skies may clear across the
Metroplex. With considerable near-surface moisture in place along
with very light winds, there may be a potential for IFR cigs (and
vsbys). With considerable uncertainties regarding this potential,
we'll keep things more optimistic for the time-being, but a more
pessimistic outlook may be needed in later TAFs. IFR (even LIFR)
conditions appear to be in store for Waco as the next slug of
moisture rides northward overnight. Conditions will improve
quickly during the mid-morning hours on Thursday. Winds will
likely briefly shift out of the west before southerly winds return
during the late-afternoon and evening.

Carlaw

&&

.SHORT TERM... /Issued 331 PM CDT Wed Jun 20 2018/
/Tonight/
Tropical moisture will continue to be shunted to the east tonight
which will keep the majority of showers and storms east of the
forecast area. However, the eastern zones will still see some
scattered activity mainly through sunset.

There is also a chance for additional shower and thunderstorm
development late this afternoon/early evening generally north of
the forecast area in the vicinity of a weak cold front and
shortwave. If these storms do develop they will move southeast
into North Texas, affecting locations generally north of I-20.
Instability across the northern half of the region is marginal
and moisture will be decreasing through the night so storms may
have difficulty holding together. Therefore, we will keep PoPs
fairly low this evening/overnight.

Overnight lows will be generally in the lower and middle 70s with
a light south to southeast wind.

79

&&

.LONG TERM... /Issued 331 PM CDT Wed Jun 20 2018/
/Thursday Onward/

Thursday should begin with a relative lull in precipitation with a
stalled frontal boundary positioned through southern Oklahoma. The
plume of rich moisture that had brought portions of North and
Central Texas some beneficial rainfall will be shifting to the
south towards Mexico, leaving us with substantially lower PW
values. This will also mean fewer clouds than previous days, so
temperatures will warm quickly as we return to near/above normal
highs Thursday afternoon. As a shortwave pivots through the
Central Plains, this may force the stalled front to enter North
Texas by Thursday afternoon. This boundary could serve as a focus
for convective initiation Thursday afternoon during peak heating
with weak low-level convergence occurring near the diffuse frontal
zone. The mostly likely area would be north of I-20 and east of
I-35. Unlike the previous few days, our the environment will have
fewer tropical characteristics, and instead will be more unstable
with steeper lapse rates aloft and some drier mid-level air in
place. These condition would support a threat for some stronger
storms in these areas capable of strong winds or some hail through
Thursday evening.

After a couple days of near or below normal temperatures, Friday
will be a rude awakening that it is, in fact, summer in North
Texas. The upper ridge will build back in from the west, and
temperatures will climb into the upper 90s and low 100s west of
I-35 both Friday and Saturday. In addition, we'll keep some
residual low-level moisture around with dewpoints in the upper
60s and 70s which will contribute to heat index values at or above
105 degrees. It's possible a Heat Advisory will be needed during
the Friday/Saturday time period if it appears these conditions
will materialize. Both Friday and Saturday evenings, we will need
to keep an eye on convection to our north as storms are expected
to develop along the stalled front draped through Oklahoma. Some
of this activity could affect our Red River counties on Friday
evening. However, models are becoming quite a bit more aggressive
with suggesting an MCS will build into North Texas on Saturday
night. I've raised and expanded PoPs overnight Saturday into
Sunday morning for areas including the DFW Metro. Conditions are
actually reasonably favorable for a robust MCS to be maintained
into North Texas during this time, with northerly Corfidi vectors,
very large instability, and strong low-level warm advection. Some
strong winds would be possible if the complex can sustain itself
into North Texas.

Following the potential early morning complex, Sunday should be a
mostly dry day with temperatures a couple degrees cooler than
Saturday, although heat indices near 105 will still be possible.
We'll remain on the periphery of the upper ridge axis Monday
through Wednesday, and temperatures will remain mostly in the
mid/upper 90s. Outside of some low rain chances associated with
seabreeze convection across our southeast on Monday and Tuesday,
it appears most of the area will remain dry early next week.

-Stalley

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    75  95  77  98  80 /  30  20  10  10  10
Waco                74  94  76 100  78 /  20  20   0   5   0
Paris               72  91  71  92  75 /  40  40  30  30  20
Denton              74  95  74  99  79 /  30  20  10  10  10
McKinney            72  93  71  96  73 /  30  30  20  10  10
Dallas              75  95  78  98  80 /  30  20  10  10  10
Terrell             73  94  75  98  78 /  30  30  10  10  10
Corsicana           72  92  75  97  76 /  30  20   5  10   5
Temple              72  93  74  99  76 /  20  20   0   5   0
Mineral Wells       72  96  73 100  78 /  30  10   5   5  10

&&

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

90/25

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Special Weather Statement
National Weather Service Fort Worth TX
637 PM CDT WED JUN 20 2018

TXZ093-210030-
Grayson TX-
637 PM CDT WED JUN 20 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTHERN GRAYSON COUNTY UNTIL
730 PM CDT...

At 632 PM CDT, Doppler radar was tracking a cluster of strong
thunderstorms approaching the Red River. One storm was near New
Woodville in Marshall County, and another was near Mead in Bryan
County. The cluster is moving south at 15 mph.

Half inch hail and wind gusts up to 50 mph will be possible with
these storms.

Strong thunderstorms will be near...
  Eisenhower State Park and Denison Dam around 725 PM CDT.
  The City of Denison and Pottsboro around 730 PM CDT.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If on or near Lake Texoma, get out of the water and move indoors or
inside a vehicle. If you can hear thunder, you are close enough to
be struck by lightning. Do not be caught on the water in a
thunderstorm.

&&

LAT...LON 3389 9663 3390 9659 3388 9659 3385 9663
      3384 9662 3382 9658 3382 9653 3377 9650
      3378 9643 3373 9638 3359 9638 3369 9686
      3385 9687 3385 9684 3387 9683 3387 9680
      3383 9677 3382 9675 3384 9669 3392 9667
TIME...MOT...LOC 2332Z 011DEG 11KT 3397 9666 3396 9650

25

Special Weather Statement
National Weather Service Fort Worth TX
713 PM CDT WED JUN 20 2018

TXZ092-093-210100-
Grayson TX-Cooke TX-
713 PM CDT WED JUN 20 2018

...SIGNIFICANT WEATHER ADVISORY FOR COOKE AND GRAYSON COUNTIES UNTIL
800 PM CDT...

At 711 PM CDT, Doppler radar was tracking a strong thunderstorm over
Lake Texoma, or 13 miles northwest of Denison, moving south at 10
mph.

Half inch hail and wind gusts up to 50 mph will be possible with this
storm.

Other storms within Grayson and Cooke counties will also be capable
of producing gusty winds and small hail.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If on or near Lake Texoma, get out of the water and move indoors or
inside a vehicle. If you can hear thunder, you are close enough to
be struck by lightning. Do not be caught on the water in a
thunderstorm.

&&

LAT...LON 3395 9691 3387 9689 3387 9680 3382 9676
      3384 9669 3392 9667 3389 9658 3385 9663
      3373 9638 3340 9639 3343 9748 3391 9748
      3383 9746 3382 9738 3388 9733 3392 9721
      3385 9717 3379 9721 3372 9714 3395 9698
TIME...MOT...LOC 0011Z 351DEG 8KT 3387 9675

25