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

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003
FXUS64 KFWD 281806
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
106 PM CDT Sun May 28 2017

.AVIATION...
18 UTC TAF Cycle

Concerns---IFR cessation at select Metroplex TAF sites, otherwise
MVFR through the afternoon and early evening with a potential for
-SHRA/TS at all TAF sites. VFR this evening, with a low chance for
additional convection after 00 UTC.

For the Metroplex TAF sites---Intermittent IFR cigs have persisted
at a few sites across the Metroplex early this afternoon in the
presence of modest low level ascent. Some of these IFR cigs may be
perpetrated by the very shallow ascent, but this is expected to
end shortly. Most cigs should lift into the MVFR category (around
FL015) this afternoon as more robust convection likely helps in
overturning the boundary layer. The next challenge will be the
timing of this convection. At this time current lightning data
indicates the convection to the west is not overly impressive in
terms of its lightning production, so I`ll simply prevail -SHRA
at all Metroplex TAF sites. If activity to the west starts showing
more signs of generating additional lightning, then a quick
amendment to include VCTS/TS may be necessary. VFR is expected to
return late this afternoon and into the early evening hours. There
is a potential for additional VCSH and perhaps VCTS around the
00-03 UTC time period, but confidence is too low to include in the
TAFs at this time. Should convection occur, the main impacts
would be potentially small hail and perhaps gusty winds/turbulence
below the cloud base.

For the Waco TAF site---MVFR will continue through the early
afternoon before the late May sun helps to erode cigs from the
south and east. With the front still located to the north of the
Waco terminal and increasing instability ahead of this feature,
there appears a reasonably high enough chance for TS at the
terminal. I have moved up the timing of VCTS by several hours
(closer to 22 UTC) to account for this and it`s possible that a
prevailing group for TS may be warranted in future amendments. The
chances for convection should dwindle this evening, but the
trends will need to be monitored. Main hazards with thunderstorms
will be hail and strong winds. Reductions to visibility and
ceilings will also be possible.

24-Bain

&&

.UPDATE...
A chance for showers and storms continues across nearly all of
North and Central Texas for the remainder of the day, but the
actual and expected locations of the surface front, and 925-850
mb fronts is challenging the forecast some. The surface front
continues to make progress through our southwest counties, as seen
on the KGRK radar; however the surface front is hung up more
across our central and eastern counties, roughly near a line from
Hillsboro to Canton. Showers and light rain have been ongoing
just north of the stalled surface front along the 925-850 mb
frontal zone where lift is occurring up over the shallow surface
boundary.

Currently, a weak, positively-tilted upper level trough is moving
into the Texas Panhandle and western Oklahoma and will continue
moving east this afternoon. This should help to move the surface
and 925-850 mb fronts south through the afternoon hours, but both
of these areas will be sources for lift. The better lift will
occur along the surface boundary where surface based CAPE values
over 4000+ J/kg are forecast by several models. We anticipate
storms will develop around or after 3 pm along this boundary. Wind
shear values today are notably lower at about 20-25 kts, but a
severe weather threat will still exist. We think the best location
for the severe threat will be along and south of a Lampasas to
Athens line. Due to the lower wind shear values, storms are
expected to evolve into multi-cell clusters and generally present
a messy appearance on radar. Hail and damaging winds will be the
main hazards with strong and severe storms, along with lightning.
The threat for storms will continue in this same area through the
evening hours and into the overnight hours, and the severe
weather threat is expected to diminish later this evening.

North of the surface frontal boundary, a potential for isolated to
scattered showers and storms remains as lift increases with the
approach of the upper level trough. The main focus for post-
frontal showers and storms is expected to be along the 925 and 850
mb fronts, and the location of rain is highly dependent on the
speed of these fronts. We will be utilizing mesoanalysis tools and
short term hi-res guidance through the afternoon hours to monitor
these fronts. Based on uncertainty in their location and speed due
to discrepancies between the models, have expanded low PoPs
farther north to the Red River through the afternoon hours. There
is some elevated CAPE above the surface inversion as evident on
the 12Z FWD sounding and forecast soundings through the afternoon,
so some hail and gusty winds cannot be completely ruled out with
any post-frontal storms.

For the remainder of the update, adjusted high temperatures based
on the ongoing trends which mostly means the highs were lowered a
few degrees in several locations.

JLDunn

&&

.PREV DISCUSSION... /ISSUED 332 AM CDT Sun May 28 2017/
Complex of severe thunderstorms is ongoing along the southward-
sinking cold front this morning. This activity has shown some
weakening trends in the past hour and this should continue as it
moves farther south. The cold front has undercut this convection
and outflow has surged out ahead, but it will continue to feed on
the elevated instability present with steep lapse rates in the
700-500mb layer. As a result, all convection is expected to fall
below severe limits by sunrise, but remaining thunderstorms will
be capable of gusty winds and small hail as the remnants of the
complex sink towards Hwy 380 and eventually I-20. Due to cell
training with storm motion roughly parallel to the cold front,
some localized flooding will also be possible in the next few
hours.

The cold front will continue to push southward today, resulting
in additional isolated to scattered showers and storms throughout
the afternoon hours. Later this afternoon and evening, the front
should be positioned across Central TX where it is expected to
slow down and eventually stall. This boundary should be capable of
initiating additional strong or severe storms across Central
Texas after 3 PM today and continuing into the evening. The severe
potential will arise mostly from the ample instability as wind
shear will be lacking. The 20-30 kts of shear will be sufficient
for a multicellular storm mode which could produce some pulse
severe hail and downburst winds. Without sufficient shear for
stronger rotating updrafts, the potential for large hail won`t be
very high. Areas across North TX should remain mostly dry during
this time, but have left a storm mention with a 10% PoP as there
will still be plenty of elevated instability; any weak ascent from
the upstream trough would be capable of generating an isolated
storm or two.

Some noteworthy height falls will overspread the frontal zone late
this evening and overnight which should result in an uptick in
broad rain and thunderstorm activity mostly across Central TX
overnight into Monday morning. Severe storms aren`t expected
during this time frame, but rather more of a broad rain shield
with embedded storms along and north of the frontal zone as weak
isentropic ascent occurs. There should a downward trend in
convection on Monday with only lingering rain chances across our
far southeastern zones without much ascent available.

The remainder of the week will be active with chances for showers
or storms each day. At this point, the highest chances will be on
Thursday and Friday with a lower potential on Tuesday and
Wednesday. Activity will mostly be diurnally driven with
instability maximized in the afternoon each day. Several weak
upper disturbances will move through the Southern Plains
throughout this time which will be capable of generating
scattered showers and storms. Shear will be minimal during this
time and a diffuse upper pattern without any focusing surface
boundaries will mean the potential for any organized severe
weather is very low. However, there could be a couple strong
storms throughout the week just due to the instability profiles.
We`ll likely remain active into next weekend with broad upper
troughing continuing across the western US. We may get another
cold front and a higher potential for more organized storms next
Saturday or Sunday as a trough sharpens and deepens to our west.

-Stalley



&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    79  68  87  67  87 /  50  10  10  10  20
Waco                85  67  84  65  86 /  40  40  40  20  20
Paris               78  64  84  63  85 /  30  10  10   5  20
Denton              80  63  87  62  88 /  30  10  10   5  10
McKinney            79  65  85  63  86 /  30  10  10  10  20
Dallas              80  69  87  68  87 /  50  10  10  10  20
Terrell             79  67  84  65  85 /  50  20  20  10  20
Corsicana           83  68  83  67  84 /  40  40  40  20  20
Temple              86  67  83  66  85 /  60  50  40  30  30
Mineral Wells       81  61  86  61  87 /  20  10  10  10  20

&&

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

$$

24/82



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