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

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FXUS64 KFWD 252116
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
416 PM CDT Thu May 25 2017

.DISCUSSION...
Hot conditions will continue over the next several days with near
100 degree ambient and apparent temperatures possible. There will
be a highly conditional risk for showers and thunderstorms on
Saturday as a dryline and cold front approach. The better risk for
showers and thunderstorms is expected late Saturday and into
Sunday when a late-season cold front will slowly slide through the
area. This frontal boundary is expected to stall across Central
TX and the Hill Country for the latter half of the holiday
weekend. This boundary may also serve as a focus for additional
rain chances through next week.

Low level moisture continues to lift northward into North and
Central TX this afternoon as surface dewpoints have steadily
increased into the upper 50s and low 60s. A modestly thick veil of
cirrus continues to overspread from the west along the northern
periphery of the H5 subtropical ridge located to the south.
Despite the general increase in high level cloudiness, a south-
southwest component to the breezy surface wind speeds has still
allowed for toasty conditions with temperatures in the upper 80s
and mid-90s across much of North and Central TX.

For tonight, a very mild night is anticipated as 925mb winds
crank up to around 45 to 50 knots. Forecast soundings do indicate
that low level thermal fields will still support some mixing
despite the onset of nocturnal cooling. The 925mb winds are
forecast to decrease after sunrise on Friday. The increasing low
level moisture and resultant cloud cover combined with the breezy
conditions should result in low temperatures only falling into the
low to mid 70s. While stratus will be on the increase, little to
no precipitation (outside of perhaps a sprinkle or two early
Friday morning) is anticipated as strong capping and mid-level
ridging continues.


For Friday, precipitation-free conditions will prevail, despite
the increase in low level moisture and the closer proximity of the
dryline to North and Central TX. This lack of rain will largely
be due to the stout capping remaining in place across the area as
southwesterly flow aloft continues. Ahead of the dryline, it`ll
feel quite oppressive. The culprit will be the lack of mixing and
loosening of the surface pressure gradient (resulting in weaker
wind speeds). These factors coupled with continued moistening
below the temperature inversion will result in heat index values
in the 100 to 103 degree range with ambient air temperatures in
the mid to upper 90s. I contemplated an impact- based Heat
Advisory for portions of North TX due to the myriad of outdoor
activities expected for the start of the Holiday Weekend, but
there`s still too much uncertainty with regards to the overall
quality of low level moisture. A majority of the dynamic NWP
appears to be slightly overdone moisture wise, as they advertise
mid to upper 70 degree dewpoints. A consensus of statistical based
guidance appears more realistic and advertises low to mid 70
degree dewpoint air overspreading North and Central TX. Heat
Advisory or not, individuals with outdoor plans on both Friday and
Saturday need to ensure that they remain hydrated with water and
take frequent breaks in cooler locations to avoid any heat related
illnesses.

In the wake of the dryline, southwest winds will be more
favorable for another day of downslope warming. This in
conjunction with deeper mixing and lower humidity will allow for
slightly more comfortable conditions for areas along and west of a
Cisco to Jacksboro to Bowie line on Friday. It will still remain
hot, however, across these locations with temperatures pushing the
century mark. Fire weather concerns/grass fire spread in the wake
of the dryline should remain limited as wind speeds are forecast
to remain below critical thresholds.

Hot and humid conditions will continue on Friday Night and into
the day on Saturday as the dryline retreats back towards the west
during the overnight hours. There could be a few streamer showers
across eastern/southern zones as low level warm air advection
commences on Saturday morning. Overall probabilities look too low
to include in the forecast at this time, but I will advertise
10-15 silent PoPs across this area. The dryline should shift
towards the east quickly through the day nearing a Wichita Falls
to Graham to Breckenridge line during the afternoon hours. A very
moist boundary layer will be strongly capped through the day which
should keep thunderstorm chances low through the morning and
afternoon hours. The low level wind field also appears to veer
through the day as greater surface pressure falls occur across
northeastern Oklahoma. With a majority of the large scale ascent
forecast to remain to the north, veered low level flow and a
strong cap, thunderstorm chances appear bleak in the afternoon
hours. However, the large reservoir of moisture coupled with steep
lapse rates and decent deep layer wind shear create a
conditionally unstable atmosphere across much of North TX. IF a
storm is able to breach the cap, it will have the potential to
become severe very quickly, with large hail and damaging winds
being the main hazards. While the overall surface wind field is
expected to remain veered, there is a non-negligible amount of 0-3
km CAPE and so the tornado potential will need to be monitored.
That said, the large hail and damaging winds will be the front
runners in the storm hazards department. We do not expect a
complete washout on Saturday afternoon and even most of Saturday
evening.

Late Saturday evening into early Sunday morning appears to be the
best opportunity for widespread showers and thunderstorms as
models have slowed the progression of the late-season cold front.
While the time of day would not be ideal for severe weather, there
appears to remain a large amount of instability and wind shear
aloft for strong to severe thunderstorms during the overnight
hours. The main hazards will remain large hail and strong winds,
especially if thunderstorms can remain rooted in the boundary
layer. With the front progressing quite slowly, there may be a
concern for some heavy rainfall. At this point in time, there is
some uncertainty in the exact areal coverage of convection, but if
rain/storms are widespread and slow moving, a flood/flash flood
threat may materialize. Rain chances look to linger during the
latter half of the weekend and into Memorial Day, especially
across Central TX. For now, will continue with 30-40% PoPs as the
850mb front lingers near the I-20 corridor. A repeat of last
Sunday is quite possible with elevated convection developing near
this elevated boundary. For now, we will keep tabs on this
potential as there still remains some uncertainty with the
placement of the surface and 850mb fronts.

For next week, the active pattern looks to continue as the old
frontal boundary remains across the region. With the ample
moisture in place and a slow moving upper trough to the west (with
likely multiple perturbation rippling through the flow),
generally broad brushed rain chances were kept in the forecast.
Given the time of year, there may be a risk for strong to perhaps
severe storms, so stay tuned to the forecast.

24-Bain

&&

.AVIATION...
/ISSUED 100 PM CDT Thu May 25 2017/
/18Z TAFs/

VFR conditions will prevail this afternoon and evening with gusty
south winds. Some cirrus will invade from the west, but no clouds
are expected within the boundary layer until early Friday morning.
A powerful low-level jet may reach 50kts at 925mb, and MVFR stratus
will race north. A strong cap will limit mixing Friday, but the
late May sun will eventually lift and erode the layer, and
scattered CU will prevail from late morning through the afternoon
hours. A dryline may come within 100nm of the Metroplex terminals,
which should somewhat reduce the speed and vigor of the winds on
Friday, but there should still be enough momentum from the
decaying LLJ to assure some gusts, particularly as the stratus
thins. The stratus will return again Friday night, likely a couple
hours earlier than the preceding night.

25


&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    75  94  77  92  74 /  10   5  10  20  40
Waco                75  92  76  92  75 /  10  10  10  10  20
Paris               69  88  74  87  71 /  10   5  10  20  50
Denton              74  93  76  92  72 /  10   5  10  20  40
McKinney            73  91  76  91  73 /  10   5  10  20  40
Dallas              76  93  77  92  75 /  10   5  10  20  40
Terrell             72  90  76  90  73 /  10  10  10  20  40
Corsicana           73  91  76  90  74 /  10  10  10  10  30
Temple              74  92  76  92  74 /  10  10  10  10  10
Mineral Wells       73 100  75  96  72 /  10   5  10  20  30

&&

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

$$

24/24


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