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

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FXUS64 KFWD 210936
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
436 AM CDT Fri Apr 21 2017

.DISCUSSION...
After a generally quiet week weather-wise, widespread rain
chances and the potential for severe weather return to the
forecast for today (Friday) and will linger through the morning
hours on Saturday. Breezy north winds are expected once
precipitation clears on Saturday with below normal overnight
temperatures Saturday night into Sunday morning. Temperatures
should moderate through the rest of the weekend and into the first
half of the new work week with precipitation-free conditions. The
middle to end of next week appears active with a chance for
showers and thunderstorms.

The immediate short term wx concern will be the area of
convection across portions of western North TX along a stalling
frontal boundary at this hour. Overall radar presentation
indicates that this convection is becoming a bit more disorganized
as it heads into a more unfavorable airmass for convective
longevity. As a result, will confine PoPs to mainly the Red River
with generally nil rain chances everywhere else.

A general increase in cloudiness is expected today as low level
moisture streams northward in response to the main upper low that
is forecast to swing southeastward towards the OK and KS border.
The resultant cyclogenesis across the panhandle should ensure that
the stationary front currently across the Red River Valley should
lift rapidly to the north. This is where the short term forecast
becomes a bit more complicated as there are potential caveats that
could keep this boundary further south. The first wave of
convection continues to push eastward as advertised across east
central Oklahoma. As the upper low approaches, increasing forcing
for ascent in the form of strong thermal advection and
subsequent isentropic ascent will likely lead to the additional
development of numerous showers and thunderstorms further to the
west. Much of the hi-resolution model guidance advertises this
uptick in convection quite well and regional radars indicate that
the second wave of convection is developing across the OK/TX
panhandles. A bulk of this activity should remain to the north of
North TX, but it`s possible that a few storms may skirt the
immediate Red River zones today, and I`ve included a mention of
low PoPs/kept lower temperatures here to account for this. More
importantly, however, is that this convection may serve to hinder
the frontal boundary`s northward progression. If the boundary is
able to sink back farther to the south, this could be a catalyst
for additional convective development early this afternoon. If
storms occur here, they would more than likely become severe with
large hail, damaging winds and perhaps a small area near the
boundary (or any outflow boundaries) may be favorable for a
tornado or two. With that in mind, this scenario does not appear
very likely as the strong height falls forecast to occur across
the OK/KS border and resultant surface cyclogenesis should help
lift the boundary northward, even in the presence of convection.
That said, we will monitor the position of the boundary closely.

Later this afternoon, the strong shortwave will continue to eject
eastward into the Ozarks and will likely send the cold front
quickly to the south. With the airmass across North TX being
conditionally unstable (forecast soundings indicate a cap will be
in place), sufficient mesoscale ascent along the front should be
enough to lift parcels to through the cap (and/or weaken the cap)
and up to their LFCs for rapid ascent into the free atmosphere.
Instability values are progged to climb into the 1500-2000 J/kg
range with deep layer shear values on the order of 40 knots. These
values would suggest that storms that develop initially will have
supercellular characteristics, capable of large hail and damaging
winds. As noted above, there may be a brief window for a tornado
or two should storms interact with any boundaries. This potential
is low, but will bear monitoring. With deep layer shear vectors
oriented parallel to the cold front, it`s likely that activity
will morph into a squall line, quickly. This should mostly
relegate the severe hazards to damaging winds and large hail. Most
model output progresses the front quickly towards the south and
this may favor elevated convection as updrafts initially rooted in
the boundary layer become undercut by the cooler, denser airmass.
Should this occur, the severe hazard scale would tip more towards
large hail than damaging winds with a diminishing threat (though
non-zero) for tornadoes. The progressive nature of the front
should also mean that prolonged periods of training echoes should
be at a minimum, but we won`t write off the possibility of some
isolated flooding, especially in urbanized areas of North and
Central TX.

Showers and storms should continue to push southward through
Central TX during the overnight hours. The severe weather threat
should wane here for a couple of reasons. 1) Convection will
likely be removed from the best upper level support and thus deep
layer shear decreases with southward extent and 2) the time of
day isn`t overly conducive for widespread severe weather. With
those two factors in mind, will keep the mention of severe wx out
of southeastern and southern zones for now. Should the convective
line be more robust than currently thought, a severe wx threat may
exist even further to the south.

The main weather highlights for Saturday morning and Saturday
afternoon will be decreasing rain chances in the morning, followed
by breezy conditions post-FROPA. Surface pressure rises should
help create breezy northerly winds of 15 to 20 MPH. Some gusts to
near 30 MPH are also expected, especially for areas that clear and
are able to mix some of the higher momentum aloft down to the
surface. At this time, sustained wind speeds should remain below
wind advisory status and I don`t anticipate one being needed at
this time. That being said, there are likely numerous outdoor
festivities ongoing this weekend and those with high profile
objects or sensitivity to the wind should take precautions to
secure any loose articles. Cooler conditions are forecast on
Saturday with most areas in the 60s and 70s for high temps.

Sunday through Wednesday appears quite dry with moderating
temperatures each day. Sunday morning will likely be the coolest
morning we`ve experienced in a while, with low temperatures in
the 40s. Some upper 30s may even be possible along the Red River,
but at this time it appears that winds may stay elevated enough to
preclude this. We will evaluate this with the afternoon and next
overnight package, however. Temperatures will be near normal
starting off next week with mostly dry conditions.

The middle to end of next week, however, appears that it`ll be
quite active, as one would expect for this time of year. There is
a general consensus in model output that low level moisture will
facilitate healthy amounts of instability. The quasi-zonal flow
aloft should ensure that deep layer shear values will promote
organized storm structures. While it`s a little too early to delve
into the specifics, it does appear that a risk for strong to
severe storms will accompany any shortwave troughs that ripple
through the flow aloft.


24-Bain

&&

.AVIATION...
/ISSUED 1118 PM CDT Thu Apr 20 2017/
Convection has erupted and will continue to erupt across Oklahoma
overnight as a mid level shortwave moves into the Southern Plains.
Storms will be focused mainly in the vicinity of a stationary
front, which should remain draped across northwest Texas and
Oklahoma for the rest of the night. A couple of right-moving
supercells have the potential to cross the Red River in the next
few hours, but these storms should still remain north of TAF
locations during the overnight hours. As the shortwave moves
farther east on Friday, the front will surge south, bringing with
it a round of showers and storms in the DFW area likely in the
02-04 Z time frame Friday evening. Activity will attempt to
backbuild southwest towards the Waco area, which may lead to an
isolated storm or two near KACT after 22/06Z.

Ahead of the system, we should see another round of MVFR stratus
develop and spread quickly north across the area. MVFR conditions
first thing Friday morning will gradually improve throughout the
day, becoming VFR by mid Friday afternoon.

30


&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    86  54  68  50  74 /  20  70  30   0   0
Waco                84  56  69  47  74 /   5  60  60   0   0
Paris               82  53  64  44  71 /  20  60  50   0   0
Denton              85  52  67  44  73 /  20  80  10   0   0
McKinney            84  54  67  46  73 /  20  70  30   0   0
Dallas              86  55  69  50  75 /  20  70  30   0   0
Terrell             83  56  68  47  74 /  10  50  50   5   0
Corsicana           85  58  69  46  74 /   5  60  60   5   0
Temple              86  57  69  49  74 /   5  50  50   0   0
Mineral Wells       85  52  68  42  74 /  20  60   5   0   0

&&

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

$$

05/24


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