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

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132
FXUS64 KFWD 281646 AAC
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1146 AM CDT Sun May 28 2017

.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

&&

.AVIATION...
/ISSUED 1020 AM CDT Sun May 28 2017/
Tricky aviation forecast for the remainder of this morning and
into the mid-afternoon time frame. Radar imagery at this hour
indicates a narrow band of light rain showers, likely indicative
of some weak ascent atop the shallow cool frontal surface. IFR
cigs will likely occur near this boundary which appears to be
pivoting just near D/FW International and extends southward
towards GKY Municipal. Given the stalemate between moist ascent on
the southeast side of this boundary moving northward and slightly
drier air sliding in from the north and northwest, the net motion
of this boundary should be near zero. Bottom line for aviation
partners at DFW and GKY is a period of IFR ceilings and perhaps
visibility with -RA continuing. As a result, I have included
temporary IFR cigs for these two airports through 18 UTC. On
either side of this boundary, slightly better flying conditions
are expected at FTW, DAL and AFW, but still MVFR cigs and at times
vsby. Should this boundary near any of these sites, however,
there could be a chance for some prolonged IFR, but we will
monitor this as the morning continues.

Alterations to the Sunday mid-afternoon hours of the TAFs were
coordinated with ZFW for a longer duration of MVFR. 925mb
moisture should remain abundant and is expected to result in
ceilings between FL018-FL022. Thereafter, northerly winds should
gradually scour out this moisture and allow for a return to VFR.

No significant changes were needed at Waco at this time, but we
will monitor the potential for convection a little later on today.

24-Bain

.../PREVIOUS AVIATION DISCUSSION/...
/12Z TAFs/

Relatively challenging first 6-12 hours of today, as DFW airports
remain in the wake of a departing MCS with an outflow boundary
that stalled across the area. Luckily, a surface cold front is
now entering the Metro and will result in prevailing north flow
10-15 kts much of the day, before becoming north less than 10
knots this evening. The large cirrus anvil from the MCS to the
east continues to migrate east away from the area, which will
allow strong late May heating to work upon a moist boundary layer
this morning for MVFR cigs. The MVFR cigs will prevail likely til
midday, before lifting into VFR with a slowly rising frontal
inversion. VFR cigs will likely scatter before or at sunset, as
some drier air filters in from the northwest.

Waco regional airport is a bit tricker, as a gravity wave from the
departing MCS is helping lift rich boundary layer moisture and
combining with increasing insolation for a band of MVFR cigs at
this airport as well. South-southwest winds around 10 knots will
prevail through early afternoon, before the slowing surface cold
front moves through the area between 18z-21z when winds will shift
initially northwest around 10 knots, then become northerly by this
evening. MVFR cigs will linger a bit longer at Waco with an
initial shallow frontal push, but cigs should eventually lift
into the VFR category by mid-late afternoon with heating/mixing.
Will carry only VCSH through much of the day here, as we await
daytime heating and a more substantial mid level shortwave and
lift arriving this evening. It is possible that the bulk of the
convection tonight remains south of Waco, but for now will hold
it in the forecast.

05/

24


&&

.UPDATE...
A weakening cluster of thunderstorms continues to move eastward
across the I-20/I-30 corridors from Dallas and Rockwall, east
through an area from Paris to Emory this morning. We have gone
ahead and canceled the Severe Thunderstorm Watch, as veering and
weakening of the 925mb LLJ continues through sunrise. In addition,
the better lift is shifting east of the area with the departure of
a strong shortwave disturbance currently moving over the Ark-La-
Tex early this morning. At the surface, outflow from the storm
complex is beginning to stall around or just south of the I-20
corridor. The true surface cold front was farther back to the
northwest and moving into areas well west of I-35/35W corridor.
The front should continue it`s progressive southeast movement
this morning, before it loses upper support with strong afternoon
heating slowing it down and likely stalling it across our far
south-southeast counties this afternoon.

For the morning hours, look for best convective chances to
continue across our far east-central counties in vicinity of any
lingering mid-level ascent and near the stalling outflow
boundary. Though a few strong storms with small hail and brief
heavy rainfall are possible, the severe weather threat is expected
to be non-existent as 925mb flow continues to veer and weaken
after sunrise. More scattered to numerous thunderstorms will
develop in the vicinity of the the stalling surface front south
of I-20/I-30 corridors. Strong daytime heating will result in high
instability with another shortwave disturbance providing lift.
Strong to severe storms are expected once again with damaging
winds and large hail being the primary threats.

05/26

&&

.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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