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

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FXUS64 KFWD 212000
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
300 PM CDT Sat Oct 21 2017


.SHORT TERM...
/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...
/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

&&


.AVIATION... /Issued 1245 PM CDT Sat Oct 21 2017/
Main concern through the TAF period is the anticipated squall
line and cold front set to arrive late tonight. Storms will affect
all TAF sites during the overnight period, although the fast-
moving nature of the line will only cause impacts for 2-3 hours at
any given site.

Throughout the remainder of the afternoon and evening,
predominantly VFR conditions are expected with the exception of
some lingering MVFR cigs around 2500 ft at western DFW Metroplex
airports. Rain is generally not expected at TAF sites through the
next several hours with only very isolated showers possible
through this evening. Later tonight, a line of storms will take
shape across West TX and western OK which will move southeast
immediately along the cold front. This should begin affecting DFW
Metroplex TAF sites around 05z, but will likely begin causing
substantial impacts to TRACON cornerposts a couple hours earlier.
Strong winds will be the main concern with this line, and gusts
in excess of 40 mph are likely in stronger storms. Any severe
segments of the line would have the potential for gusts over 60
mph. There is also a lower threat for hail or an embedded tornado
within the line. Storms will clear DFW Metroplex TAF sites by 09z
or 10z.

At Waco, similar trends can be expected, except about 3-4 hours
later on the timing. In addition, MVFR cigs may arrive prior to
the cold front, and a few hours of BKN025 cigs are possible before
the squall line arrives.

Behind the cold frontal passage, drier air will arrive and quickly
scour out remaining low-level moisture. As a result, nearly SKC
conditions should prevail through Sunday with north winds of 10-20
kts.

-Stalley

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    60  76  51  82  54 / 100   5   0   0   0
Waco                61  77  49  82  52 /  90  10   0   0   0
Paris               59  70  49  77  50 / 100  10   5   5   5
Denton              57  74  49  82  51 / 100   5   0   0   0
McKinney            58  73  49  80  52 / 100  10   0   0   0
Dallas              60  77  52  82  54 / 100  10   0   0   0
Terrell             60  74  48  81  51 / 100  10   0   0   0
Corsicana           62  73  49  79  52 / 100  20   0   0   0
Temple              62  77  49  82  52 /  90  10   0   0   0
Mineral Wells       57  73  47  83  49 / 100   5   0   0   0

&&

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

$$

26/91


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