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

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390
FXUS64 KFWD 210459 AAC
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1159 PM CDT Sat May 20 2017

.AVIATION...
/06Z TAFs/

Concerns...Convection around KACT and near the Metroplex.

Showers and thunderstorms have been expanding the past 1-2 hours
as a shortwave moves through the region. Expect isolated to
scattered showers and storms to occur in Central Texas, including
around KACT, for much of the night. Will carry a mention of VCSH
for a few more hours and then transition to VCTS after 09Z. I
anticipate the rain activity in Central Texas will experience a
brief lull for some of the day on Sunday but timing that lull in
difficult. It should be in the late morning and afternoon hours,
and then another round of rain is expected overnight Sunday-
Monday.

For the DFW airports, showers and isolated storms are moving
northeast across the southern portions of the Metroplex, just
ahead of the 850 mb front. KGKY has the best chance for
precipitation at the airport, but will carry a mention of VCSH at
all the TAF sites for 1-2 hours. Most of the precipitation should
be south of the airports for the remainder of the night and
Sunday morning. Another round of rain is expected late Sunday
night.

North to northeast winds will prevail tonight and gradually become
east by Sunday afternoon.

JLDunn

&&

.UPDATE...
Scattered showers and storms continue in the vicinity of what now
appears to be a stationary front just south and east of the
forecast area. Thunderstorms continue to fire just outside of
Leon and Anderson Counties, which is where we will keep some
chance POPs this evening in case any northwestward moving outflow
sets off additional activity. Meanwhile,the 850 MB front appears
to be situated just south of the I-20 corridor and is moving
little. The proximity of the front may aid in the development of
elevated showers or storms overnight across the southern half of
the region as weak disturbances pass overhead in the southwest
flow aloft. We will have slight chance POPs around I-20 overnight
with increasing chances the farther south you go. Otherwise, a
pleasant night is on tap with temperatures falling into the 50s
and 60s by sunrise Sunday.

30

&&

.PREV DISCUSSION... /ISSUED 309 PM CDT Sat May 20 2017/
North TX remains situated under a dampening cyclonic flow, as an
upper low continues to lift northeast across the Central Plains
and toward the Midwest. Farther south, an active southern branch
of westerlies over South TX continued with off and on rounds of
convection occurring. A surface cold front was slowly entering our
far eastern counties, but should pick up forward speed by this
evening with support from a shortwave moving southeast across the
TX Panhandle, Northern OK, and KS.

Progressive flow aloft will continue over TX through Monday, as a
mid level deformation zone remains anchored south of I-20. In
addition, periodic waves of shortwave energy embedded in the
southern branch of the westerlies will bring occasional bouts of
scattered showers and storms Central and Southeast TX. As the
850mb front lifts back north Monday and Monday Night, richer
atmospheric moisture through 700mb will spread north across the
entire area. The increasing WAA and northward shift of the
southern branch of the westerlies will likely bring a chance for
showers and thunderstorms across the entire area, though models
are struggling mightily with timing and strength of these mid
level disturbances and location. I will maintain chance PoPs with
low confidence on where the deformation zone sets up and timing
the shortwave energy within the progressive flow aloft. High and
low temperatures will generally be 5-10 degrees below
climatological averages due to a shallow, but cool low level
airmass and the expected extensive cloudiness.

A sharper northern stream shortwave disturbance will move
southward across the Midwest, Central Plains, and Mississippi
Valley Monday Night into Tuesday, which will help draw yet
another cold front into the area on Tuesday. The best lift from
this shortwave should remain just north and east of our area, but
will be close enough to work in tandem with forcing along the
cold front to generate scattered showers and storms. Large scale
ascent should be enough for a few organized thunderstorms, but
surface-based instability looks uncertain at this time.
Nevertheless, with relatively steep mid-level lapse rates around
7 deg C/KM, we cannot rule out some strong storms or even a low
risk for a severe storm or two. The environment will be the key
here and there`s way too much uncertainty to pinpoint that at the
moment. Afterward, deep northerly flow aloft Tuesday night through
Wednesday will result in below normal temperatures, but dry
weather.

Temperatures are expected to modify and warm with the arrival of
shortwave ridging aloft and a return to southerly winds Thursday
through Saturday. A broad Western CONUS trough will organize next
weekend, but models are not handling this well. Either way, strong
southwest flow aloft will likely keep the surface dryline held
well west of North and Central TX with likely a strong EML (cap)
over the area for continued dry weather.

05/



&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    61  81  63  78  64 /  20  20  20  30  40
Waco                62  80  63  76  63 /  40  40  40  50  40
Paris               57  79  58  75  60 /  10  10  20  30  40
Denton              55  80  59  77  62 /  10  10  20  30  40
McKinney            57  81  59  77  62 /  10  20  20  30  40
Dallas              61  82  64  78  65 /  20  20  20  30  40
Terrell             60  80  61  75  63 /  20  30  20  40  40
Corsicana           63  81  63  76  64 /  30  40  30  50  40
Temple              62  80  63  78  64 /  40  40  50  60  40
Mineral Wells       55  81  59  77  60 /  20  20  20  40  40

&&

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

$$

82/30



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