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

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FXUS64 KFWD 291211 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
711 AM CDT Sat Apr 29 2017

.AVIATION...
/12Z TAFs/

The speed of the front is going to be a significant factor in
today`s weather trends at the TAF sites, and right now the front
is a few hours ahead of schedule; already moving into the
northwestern portions of North Texas and continuing to make steady
progress southeast. The short-term models are all lagging behind
with the location and speed of the front, so have played it
conservative with this set of TAFs, and much of the next several
hours may have to be spent monitoring the location of the front
and upper level low for any adjustments to the TAFs.

DFW Airports....By mid-morning, the front should stall as the low
level jet decreases, and an extrapolation in time suggests the
front may stall just northwest of the DFW TAF sites. As the upper
level low begins to spread lift into the region around midday,
scattered showers and storms are expected to develop and have
moved the timing of precipitation up to 17-21Z. Of course, if the
front actually moves through the Metroplex before stalling, the
best rain chances will likely shift east of the airports, but
there could still be a low threat for elevated thunderstorms
behind the front as large scale lift increases this afternoon.
Any storms that occur ahead of and/or along the front this
afternoon could be severe. Shower and isolated thunderstorm
chances will increase again overnight as the powerful upper level
low moves into the Plains. These storms will be elevated and may
have small hail. Strong south winds ahead of the front will become
breezy west to northwest winds behind the front. MVFR cigs should
improve to VFR with the FROPA.

Waco Airport...The faster timing of the front isn`t expected to
cause impacts at KACT in the short-term, but we will have to
monitor its position throughout the morning and early afternoon
hours for any necessary adjustments in the afternoon hours. MVFR
cigs and strong south winds will continue through the early
afternoon hours until the front arrives. For now, bring FROPA in
around 22Z with breezy west to northwest winds behind the front.
At this time, will carry a VCSH starting at 15Z with a chance for
thunder from 19-22Z. These storms could be severe. There is
another chance for showers and isolated thunderstorms overnight
as the powerful upper level low moves into the Plains. These
storms will be elevated and may have small hail.

JLDunn

&&


.PREV DISCUSSION... /ISSUED 411 AM CDT Sat Apr 29 2017/
A deep upper level low near the Four Corners appears on satellite
to be making a move eastward along the New Mexico-Colorado border.
Thunderstorms have been erupting across the Texas Panhandle and
Oklahoma overnight along and north of a frontal boundary, due to
strong forcing associated with the upper low. In fact, intense
convection stretches all the way eastward from Oklahoma across
Missouri, Illinois and into the Ohio Valley.

Locally, the regional RADAR mosaic indicates that the front is
now beginning to push southeast, possibly aided by gust fronts
from the numerous storms to the northwest. The expectation is
that the front will move into the far northwestern counties around
sunrise before slowing down as the low level jet begins to mix
out. The front may still generate scattered convection this
morning across the northwestern third of the forecast area, though
it will likely be less intense than the ongoing OK-NW TX
activity. This is advertised well by the majority of the hi-res
model guidance. One fly in the ointment, however, is the 3 KM NAM
which indicates that the storms near the TX Panhandle-OK border
will organized into an MCS. The good news is that the 06Z run
weakens this feature considerably as it moves into the northwest
counties, as opposed to the 00Z run which blasted it all the way
through the Metroplex. Since the latter run is the biggest
outlier, the current forecast will not reflect that scenario.
Nevertheless we will need to keep an eye on the evolution of any
upstream storm clusters / cold pools which may develop.

After slowing a bit following sunrise, the front will pick up
steam again late this morning as the upper low approaches the
Texas-New Mexico border. Rain-cooled air may hamper surface
heating in the northwest, but the rest of the region will have
several hours to destabilize. By early afternoon, several
parameters will be in place for the development of strong to
severe thunderstorms. A moist and highly unstable airmass, good
lift provided by the deep upper level system, and a surface
boundary to provide focus for development.

Where storms initialize this afternoon will depend on the location
of the cold front. Taking a blend of the most recent guidance
places the boundary just west of I-35/35W in that 19-20Z hour
(when convective initiation is most likely), which is similar to
yesterday`s forecast and actually near the western edge of the
latest Enhanced risk area from SPC. Storms that develop will have
a good chance of becoming severe due to the high amounts of
instability and shear present. Since shear is mostly
unidirectional, the primary severe threat will be large hail and
damaging winds. A few tornadoes will still be possible, but if
winds become more backed at the surface, a higher tornado threat
would exist.

Storms should quickly congeal into a squall line early this
evening as they push eastward through the forecast area. The
severe concern would shift to a damaging wind and possible brief
spin-up tornado threat with a gradually lowering large hail
threat. In addition, high PWATs suggest that a brief heavy rain
and localized flooding threat will also exist along the line,
particularly if there are any training segments. The line of
storms should reach the southeastern-most counties around
midnight and exit to the east shortly thereafter. Additional
showers and storms will remain possible area-wide through the
overnight hours as the core of the upper low crosses the Southern
Plains. Forcing will be strong, but limited moisture and
instability will likely preclude any additional severe threat
(though some storms may produce frequent lightning and small
hail).

Cool and dry air can be expected Sunday behind the front with
highs in the 60s followed by lows in the 40s Sunday night.
Abundant sun and the return of south winds will bring a quick end
to the cool snap on Monday and Tuesday. A fast-moving shortwave
trough will provide a chance of showers and storms around the
middle of next week, followed by upper level ridging and pleasant
weather late in the week and into next weekend.

30

&&



.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    82  52  68  49  80 /  70  50  10   0   0
Waco                84  53  71  46  81 /  50  50  10   0   0
Paris               81  54  64  46  75 /  80  80  20   0   0
Denton              80  48  65  44  79 /  70  50  10   0   0
McKinney            81  51  65  46  77 /  80  60  10   0   0
Dallas              83  53  68  50  80 /  70  50  10   0   0
Terrell             82  53  68  47  78 /  80  70  10   0   0
Corsicana           84  54  69  49  79 /  70  70  10   0   0
Temple              83  53  72  48  82 /  40  50  10   0   0
Mineral Wells       80  47  67  43  82 /  40  50   5   0   0

&&

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

$$

82/30



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