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

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403
FXUS64 KFWD 191736
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1236 PM CDT Thu Oct 19 2017


.AVIATION...
Satellite imagery shows the continued approach of a shortwave
trough over West Texas and the cirrus canopy accompanying it. The
atmosphere will moisten up tonight in advance of the system,
which will be evidenced by higher dewpoints and a deck of stratus
spreading north across the area Friday morning. MVFR CIGs have
therefore been introduced at KACT at 20/12Z, then 20/15Z in the
DFW Metroplex. The main issue in the short term is the area of
smoke and haze in the Metroplex which is believe to have
originated from a small controlled burn. There was a pronounced
inversion this morning which likely trapped the smoke near the
surface, but conditions should continue to improve this afternoon
as mixing heights increase.

Friday afternoon has the potential for convection due to increased
moisture from the Gulf and lift associated with the shortwave.
Guidance is mostly conservative with convective coverage due to
the lack of any significant forcing mechanism so TS will be kept
out of area TAFs at this time. The extended portion of the DFW TAF
will, however, include VCSH beginning 20/20Z.

30

&&


.UPDATE... /Issued 1103 AM CDT Thu Oct 19 2017/
The shortwave trough over West Texas continues to provide multiple
layers of cirrus across North and Central Texas. Due to the
transparency of the cloud deck, there should still be enough sun
to allow temperatures to climb to around 80 or so this afternoon.
Meanwhile, the strong inversion as seen on this morning`s sounding
has allowed some thin haze and smoke to linger across the
Metroplex. Hopefully a few more hours of boundary layer mixing
should allow visibilities to improve. Other than some minor tweaks
to sky grids and hourly temperatures, the forecast remains
unchanged.

30

&&

.SHORT TERM... /Issued 420 AM CDT Thu Oct 19 2017/
Despite an entire day of steady south winds, the moisture recovery
has been slow. Rich tropical moisture remains offshore, and even
where the winds have subsided early this morning, the moisture is
insufficient for any fog. The delayed arrival of the Gulf surge
means no low clouds are available to inhibit the cooling of the
surface layer, but a blanket of cirrus is filling the role.
Although there is a 4-mile thick layer of bone-dry air between the
boundary layer and the cirrus, this dense layer of high clouds is
able to disrupt the upward radiative transfer. Some locations
remain in the 60s during the predawn hours, particularly where a
breeze prevails.

VWP data has maintained 30-35kts at 2kft AGL early this morning.
Although some of this momentum will reach the surface in the form
of occasional gusts, the surface gradient will likely keep
sustained winds under 15mph. This flow will be sufficient to carry
60F+ dew points into our southern zones today, but it will likely
take until late tonight for this moisture to penetrate deep into
the CWA. The forecast wording may say mostly cloudy, but there
will be plenty of sun filtering through the cirrus today. These
high clouds may stunt the warming trend, but the low-level warm
advection and sunshine should still allow afternoon temperatures
to match Wednesday`s highs.

25

&&

.LONG TERM... /Issued 420 AM CDT Thu Oct 19 2017/
/Friday Through Next Wednesday/

The quiet weather regime the area has enjoyed for the past week
or so will slowly come to an end, as the upper ridge shunts
eastward in response to a second stronger lead shortwave arriving
by Friday afternoon. Meanwhile, warm advection and an open direct
fetch of moisture from the Gulf of Mexico will allow for some
destabilization of the environment by afternoon with highs in the
lower 80s. The EML should be stout enough for most of the morning
activity to occur underneath the warm layer and mostly in the form
of showers, though some isolated thunder certainly can`t be ruled
out just before the noon hour. The crux of the low level theta-e
advection will occur east of I-35 where precipitable water values
will likely exceed 1.5". I will carry higher thunderstorm chances
across the eastern half of the CWA, especially in the afternoon
when better instability will be realized.

The EML (capping inversion) is expected to lift and modify on
Friday afternoon, though I am suspect the high-resolution models
may be trying to weaken it too much. Either way, SBCAPE values at
or above 1000 J/KG, mid-level lapse rates near 7 deg C/km, and
westerly 0-6km bulk shear and 0-1km shear increasing toward 20 kts
late in the day tell me a few storms could easily be strong with
gusty downburst winds, frequent lightning, small hail, and brief
heavy downpours. I am concerned that if high temperatures warm
more than currently forecast lending to higher instability, that a
brief window for a severe weather threat could evolve noting the
well-defined warm advection and veering profiles in the low-mid
levels per forecast high-resolution soundings from the WRF and 3km
NAM models. The keys here will be the amount of insolation,
surface temperatures, and how quickly the EML can be lifted and
moistened from the ascent from the aforementioned shortwave.
Plenty of contingencies here, but something we`ll monitor very
closely for late day and evening outdoor events across the region.
The shortwave disturbance is expected to lift away from the area
Friday evening with a brief subsident period Friday night and
Saturday morning. This will result in a brief lull in convective
activity late Friday night into Saturday morning as we await the
main vigorous shortwave progressing across the lee of the Rockies.

The next window for increasing storm chances will begin Saturday
afternoon and last through at least mid morning Sunday, as the
much more vigorous shortwave lifts out across the High Plains with
moisture continuing to surge northward up toward a surface cold
front draped from the Central Plains to the TX Panhandle. Similar
to Friday afternoon, the axis of higher precipitable water values
will be across the eastern half of the forecast area and will
have highest chances east, diminishing to slight chances across
the west. With warmer temperatures well into the 80s Saturday
afternoon, I see a window for surface-based, potentially discrete
severe thunderstorms with southerly 0-1km shear values 15-20 kts,
but westerly 0-6km bulk shear rising to between 35-40 kts. The
strong veering low level profiles do have me concerned for
possible mesocyclone development with a few storms later in the
afternoon and through the early evening hours with LCLs fairly low
with surface dew point temperatures between 65 and 70 degrees. I
do think this window would be the highest for tornadic potential
along and east of I-35/35E where richest surface dew points will
exist. I would like to see a little better surface- based
instability, but shear profiles certainly support such a threat.

The main shortwave trough and associated cold front will rotate
across the area later Saturday evening into early Sunday, with
likely a strong line of storms or potential QLCS event along and
ahead of the cold front given the strong kinematics, shear, and
sub-tropical like environment in place. All modes of severe
weather would be possible, though the bulk of threats will likely
be associated with damaging winds and large hail. A brief spin-up
tornado or two can`t be ruled out with any embedded supercell
storms along the line or linear MCS. Either way, I can`t argue
with the SPC enhanced-slight risk areas across the area for Day 3
(Saturday and Saturday night). Otherwise, some timing differences
have been noted with both the cold front and the base of the mid
level energy swinging through amongst the models. GFS/Canadian are
more progressive with each, while the NAM/EC are 3 hours or more
slower. With these discrepancies in mind, will at least linger
higher convective chances across the southeast half of the
forecast area for sunrise to mid morning hours. Afterward, mid
level subsidence will coincide with brisk, cooler, and dry
conditions arriving Sunday afternoon and evening as the severe
threat shifts quickly east of the region.

Cooler, though more seasonable temperatures will occur Monday,
but especially on Tuesday and Wednesday, as strong northwest flow
aloft supports another reinforcing cold front into the region by
early Tuesday. Lows in the 40s to lower 50s and highs in the upper
60s to mid 70s will be common for the first half of next week.
Enjoy the rainfall this weekend, because much of next week will
see dry and mostly sunny conditions with the Gulf of Mexico cut
off and strong northwest flow aloft.

05/

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    82  65  82  68  85 /   0  10  30  20  30
Waco                83  64  82  68  86 /   0  10  50  30  30
Paris               80  58  80  64  80 /   0  20  20  20  40
Denton              82  62  81  67  84 /   0  10  20  20  30
McKinney            82  62  80  67  82 /   0  10  20  20  40
Dallas              82  66  82  69  84 /   0  10  30  20  30
Terrell             84  61  83  66  84 /   0  20  30  20  40
Corsicana           82  63  81  66  83 /   0  20  40  30  40
Temple              82  64  82  68  86 /   0  10  50  30  30
Mineral Wells       82  62  81  67  85 /   0  20  30  10  20

&&

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

$$

30/92



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