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

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000
FXUS64 KFWD 211202
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
702 AM CDT Sun May 21 2017

.AVIATION...
The primary aviation weather concern with this forecast will be
brief thunderstorms this morning and again this afternoon/tonight.

Isentropic lift was resulting in numerous showers and
thunderstorms this morning at all TAF sites. We expect this
activity to decrease rapidly after sunrise with most storms
dissipating between 14 and 15Z. There should be a regeneration of
storms this afternoon, but most likely farther south, closer to
the expected position of the 850 mb front. Therefore, Waco will
have the best chance of showers/storms this afternoon and
especially tonight.

Outside of the storms, expect VFR conditions with broken mid and
upper level clouds through Monday morning.

A northeast to east wind will prevail at speeds near or below 10
knots. The only exception will be for variable and gusty winds in
and near thunderstorms.

79

&&


.PREV DISCUSSION... /ISSUED 352 AM CDT Sun May 21 2017/
Surface analysis early this morning places an ill-defined quasi-
stationary front more or less along the 70 degree isodrosotherm
which stretches from near a Del Rio to Austin to Nacogdoches. To
the north of this feature, dewpoints gradually fall into the 50s
across roughly the northwestern half of the CWA. Aloft, the
effective 850 mb front is quite a bit farther north--laid out
almost right along the I-20 corridor--and this is resulting in
MUCAPE values in excess of 1000 J/kg to its south. Modest
isentropic upglide above this feature along the 300-310 K theta
surfaces appear to be the primary culprit in the re-development of
isolated to widely scattered showers and storms overnight. The
combination of sufficient elevated instability and effective deep
layer shear values in the 30-40 kt range are supporting some
occasionally strong pulse/multicell storms.

As the 850 front continues to slowly push southward today, the
main thunderstorm chances should likewise gradually sink south of
the I-20/30 corridors this afternoon. Based on the rather modest
nature of the warm advection today, think the HRRRs forecasted
convective coverage is a bit overzealous, and have favored chance
PoPs across our southern counties. Given the aformentioned
kinematic profile, the more rambunctious (short-lived) updrafts
could be capable of some marginally severe hail, and perhaps some
gusty winds with the help of some diabatic warming today. High
temperatures today are tricky given the splotchy precipitation and
cloud coverage, but in general, temperatures will warm into the
upper 70s to near 80 degrees or so.

Later this afternoon and evening, an uptick in convection is
anticipated across the Big Bend of Texas as a shortwave--presently
shifting eastward across Sonora, Mexico--emerges into the Trans-
Pecos region. Based on this feature`s track, it appears the bulk
of thunderstorm activity should occur across the Hill Country
tonight. There may be enough of a northward push, however, to
drive decent precipitation coverage potentially as far north as
the Metroplex late tonight, but for now, we`ll confine the likely
PoPs to south and east of a Lampasas to Athens line. While
effective shear values will be on the upswing through this period,
increasingly moist-adiabatic thermodynamic profiles will support
only limited instability. As a result, the most we`d expect from
these overnight showers/storms would be some small hail.

As this shortwave exits the region Monday morning, we may actually
be left with a fairly dry day on Monday in the shortwave`s
subsident wake. As a result, opted to trim PoPs slightly across
the region, but these may still be a bit overdone. The next
feature of interest will be a potential southeastward-advancing
convective complex that coarse and high-resolution guidance alike
is keying in on for the Monday evening and overnight period.
Synoptically, it appears this feature will have its origins across
the Texas/Oklahoma Panhandles in response to a sharp mid-level
perturbation swinging into the Great Plains Monday afternoon.
With bulk shear vectors oriented roughly parallel to the
initiating boundary (a cold front), it`s not surprising that CAMs
quickly develop an upscale-growing MCS. Investigation of upstream
forecast soundings reveal the presence of at least some mid-level
dry air which may support cold pool development, lending at least
some credibility to the CAM-depicted surging convective complex.
With this in mind, we`ve bumped PoPs up across the southwestern
half of the CWA Monday night. The severe potential with this
system is in question at this point given both the limited time
for moisture to return across the Concho Valley/Big Country and
a very unimpressive wind field below 700 mb (15 kts or less). For
now, won`t rule out the possibility of this system delivering a
strong/gusty wind threat to our western counties Monday evening
and into the early overnight hours.

We`ll hang onto low-grade PoPs on Tuesday before a reinforcing
cold front drives through the region during the afternoon. This
will result in a dry stretch of weather from Wednesday and into
the upcoming weekend. Moisture will rapidly return to the region
Thursday night and into Friday, but along with this moisture will
come the advection of a stout EML plume off the Mexican high
terrain. This will effectively curtail any threat of
thunderstorms until Sunday as a cold front and dryline impinge
upon the region from the north and west.

Carlaw

&&



.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    81  63  79  62  79 /  20  30  30  40  20
Waco                77  63  78  61  81 /  40  50  50  50  30
Paris               80  58  75  59  75 /  10  20  20  30  30
Denton              81  58  78  60  77 /  10  20  30  40  20
McKinney            81  59  77  59  77 /  20  20  30  30  20
Dallas              81  64  78  63  79 /  20  30  30  40  20
Terrell             77  61  75  61  78 /  30  40  40  40  30
Corsicana           77  63  77  62  80 /  40  50  50  40  30
Temple              78  63  78  61  81 /  50  60  60  50  30
Mineral Wells       81  58  78  59  76 /  20  20  30  50  20

&&

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

$$

79/90



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