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

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FXUS64 KFWD 220555 AAC
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1255 AM CDT Sun Oct 22 2017


.AVIATION...
A cold front extended southeast of a KGYI-KDTO-KGZN line as of
05Z. An outflow boundary that extended just southeast of the front
will be effectively overtaken by the front during the next couple
of hours. Showers and thunderstorms will continue to spread
southeast ahead of and an hour or two behind the cold front. The
outflow boundary/cold front was moving into the Metroplex around
TAF issuance time, so have started the TAFs with 32015G25KT.
Expect conditions to improve to VFR 08-09z in the Metroplex as the
showers/thunderstorms move to the southeast and skies will be
clearing by 14z. Northwest winds 20 to 25 mph will become more
northerly by 09z and these winds will prevail through most of the
daytime hours. Some gusts to around 30 knots are possible at times
through 19z. Winds will decrease to around 12 knots by 00z
Monday.

At Waco, MVFR ceilings are expected to spread north into the
airport between 06 and 07z. Winds will shift to the northwest at
15 to 20 knots 0730-0830z and some gusts up to 30 knots possible
through 10z with showers and thunderstorms. VFR conditions are
expected to return around 11z with clearing skies after 13z.
Northerly winds will decrease to around 12 knots by 00z Monday.

58

&&


.SHORT TERM... /Issued 300 PM CDT Sat Oct 21 2017/
/Tonight and Tomorrow/

The focus of the short-term forecast lies on the much-anticipated
cold front and squall line arriving during the overnight hours.
Strong or severe storms are expected to affect most of the
forecast area with the highest severe threat north of I-20. While
damaging winds will be the main threat with the squall line, hail
and a couple brief spin-up tornadoes are also possible given the
environmental conditions discussed below.

An unseasonably warm and humid airmass is in place across North
and Central TX today with temperatures climbing to near-record
values across parts of Central TX this afternoon. These
conditions have contributed to ample instability across most of
the area. However, a stout cap remains in place which will
continue to suppress deep convection through the next several
hours. Ascent is still relatively weak with the upper trough
displaced well to the northwest at this time. As a result, only
the weak lift from warm advection has been able to generate
isolated showers across areas east of I-35 so far this afternoon.
An isolated storm is possible in this area through the late
afternoon or early evening hours when instability will be
maximized, although the lack of vigorous ascent should keep
activity fairly tame.

By 6-7pm, we should see a marked increase in convective activity
through southwest OK and the TX Panhandle region along the
southward-advancing cold front with aid from an intense shortwave
trough. Additional cells may develop a bit farther south along
the dryline and near the dryline/front intersection around
Abilene. Initial development will consist primarily of discrete
cells, many of which will be capable of becoming severe, although
this activity will likely remain 50+ miles west/northwest of our
forecast area. Convection should grow upscale rather quickly as
cold pools congeal, especially given that storm motion and deep-
layer shear vectors are nearly parallel to the frontal boundary. A
QLCS should develop by late evening, prior to any convection
arriving in our forecast area from the northwest.

By 9-10pm, the squall line should be moving into our northwest
counties along the fast-moving front. As the strong shortwave
approaches, lapse rates will steepen and the cap will lift/cool.
This will allow for continued surface-based convection during the
overnight hours which means all modes of severe weather will be
possible. The main concern will be the potential for damaging
straight line winds, especially associated with any bowing
segments within the line. Some severe winds in excess of 60 mph
are likely within the forecast area overnight. Given the steep
lapse rates, stronger cells within the line will also have the
potential to produce severe hail as well. In addition, widely-
curved hodographs are expected to be supportive of a QLCS
tornado threat with 20-30 kts of 0-1 km shear in place. The
northern flanks of any bowing segments will need to be monitored
closely for tornadic potential, especially north of I-20 where the
QLCS may be oriented slightly more perpendicular to the frontal
boundary and where the most vigorous lift will occur from the
shortwave trough.

At this point, there does not seem to be much of a potential for
discrete cells to develop ahead of the front. This would further
limit the tornado/hail risk if discrete cells are not present. It
appears most of the forcing will be positioned immediately along
the front which will be surging rather quickly to the southeast.
Since storm motions should be roughly parallel to the front, any
cells ahead of the front will quickly become engulfed by the line.
That being said, some embedded supercell structures would be able
to survive within the QLCS given the strong deep-layer shear. If
any cells do manage to sustain themselves ahead of the QLCS (which
again, appears unlikely), they could pose a high-end severe
threat.

The front/squall line should affect the DFW Metroplex around
midnight or later, the Waco/Temple area by 3-4am, and should be
clearing the forecast area to the southeast around daybreak.
Lingering stratiform rain may persist through mid-morning across
our southeastern zones before drier post-frontal air scours out
remaining moisture, leaving a pleasant fall Sunday with near/below
normal temperatures and clearing skies. North winds will remain
breezy through the afternoon at 10-20 mph.

-Stalley

&&

.LONG TERM... /Issued 300 PM CDT Sat Oct 21 2017/
/Sunday Night through Saturday/

The cold front and precipitation will have moved through the area
by Sunday night leaving drying conditions and pleasant
temperatures headed into early Monday morning. High pressure will
settle into the southern Plains on Monday with diminishing winds
and temperatures in the lower 80s during the afternoon. A strong
upper trough will continue to amplify over the eastern half of the
U.S. late Monday into Tuesday. As it does, a reinforcing cold
front will move through North Texas Monday night. North winds will
increase through the night and it will become gusty during the day
Tuesday with cooler air filtering into the region. Highs on
Tuesday will only manage the lower 70s. A brief warmup will occur
on Wednesday and Thursday with highs in the 80s, then a stronger
cold front will move through on Friday. At this time, it appears
that the Friday cold front will have limited moisture to work
with, so we`ll maintain some very low PoPs. There are also some
timing differences among the guidance, but it appears that it`ll
be noticeably cooler for next weekend.

Dunn

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    51  82  54  72  48 /   0   0   0   0   0
Waco                49  82  52  75  46 /   0   0   0   0   0
Paris               49  77  50  69  43 /   5   5   5   0   0
Denton              49  82  51  72  45 /   0   0   0   0   0
McKinney            49  80  52  71  45 /   0   0   0   0   0
Dallas              52  82  54  73  49 /   0   0   0   0   0
Terrell             48  81  51  73  43 /   0   0   0   0   0
Corsicana           49  79  52  72  46 /   0   0   0   0   0
Temple              49  82  52  76  47 /   0   0   0   0   0
Mineral Wells       47  83  49  72  44 /   0   0   0   0   0

&&

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

$$

58



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