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

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FXUS64 KFWD 230013 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
713 PM CDT Sat Sep 22 2018


.AVIATION...
/00Z TAFs/

Concerns: MVFR and IFR cigs and visby through the period and
likely into Monday.

DFW Airports: The surface low is located across eastern Dallas
County resulting in north winds at all the Metroplex airports.
Wind speeds of 10-15 kts will continue for a few more hours and
then decrease to less than 10 kts through the remainder of the
period. Scattered areas of drizzle and light rain will continue
through the night, causing reduced visibilities at times, with a
few showers possible through the evening hours. Overnight, a few
showers may develop north to northwest of the airports, but have
opted to remove the VCSH after 06Z for now. IFR ceilings are
likely to continue through the valid TAF period, but a brief
period of LIFR is possible late tonight, and a period of low end
MVFR cigs is also possible during the Sunday afternoon hours.

Waco Airport: Dry conditions are expected at KACT through the
period. West to northwest winds will prevail through the period
at speeds less than 10 kts. MVFR cigs are expected to persist
through the evening hours with a lowering to IFR overnight. MVFR
cigs are expected to return Sunday afternoon.

JLDunn

&&


.SHORT TERM... /Issued 344 PM CDT Sat Sep 22 2018/
/Rest of Today and Tonight/

Regional surface analysis early this afternoon places an area of
low pressure over Dallas County with an associated warm front
snaking its way off to the northeast, from McKinney to near Paris.
A cold front trails this area of low pressure and is presently
situated just east of I-35/35E. Between these two surface fronts,
dewpoints are running in the mid and upper 70s. Just a few peeks
of insolation have allowed MLCAPE values to increase into the
700-1500 J/kg range in the remarkably moisture-rich environment.
In addition to enhanced low-level convergence facilitated by
these surface boundaries, diffluent upper-level flow is also
present across North Texas which resides under the left exit
region of a subtle 250-300 mb jet streak.

Based on recent GOES-16 visible satellite imagery, we anticipate
a gradual increase in shower and thunderstorm activity across the
warm sector through the rest of the afternoon and into the evening
hours as convective temperatures are met. The greatest coverage
looks to occur north and east of a Dallas to Ennis to Athens line,
and it goes without saying that any heftier storms will be
capable of producing high rainfall rates on the order of 2 to 3
inches per hour. In addition to the heavy rain and associated
flash flood threat, we can`t rule out the potential for a brief
tornado spin-up or two this afternoon in the warm sector where 0-3
km CAPE values overlap with 0-1 km SRH values in excess of 50-100
2/s2. The total bulk shear is rather minimal (less than 20 kts),
but enhanced hodograph curvature is noted in the lowest 3 km due
to the markedly backed surface winds in the vicinity of the
aformentioned warm front. The main threat area for a brief tornado
spin-up will be the area bounded by a Cooper to Dallas to Gun
Barrel City to Athens line where low-level instability and wind
shear most favorably coincide.

The heavy rainfall threat will continue through the evening hours
as southerly 925 mb winds of 15-20 kts maintain poleward moisture
transport across locales east of I-35/35E and roughly along and
north of I-20. Hi-resolution guidance continues to support the
potential for an additional 1-3" of rain with locally higher
amounts. As a result, the Flash Flood Watch will remain in effect
through Sunday morning across the northeastern quadrant of our
CWA, although it`s possible we`ll be able to cancel some of the
far western/southern counties early if radar and model trends
appear favorable later this evening.

Finally, forecast soundings appear favorable for drizzle/mist in
the post-frontal airmass tonight, so we`ll include a mention of
patchy drizzle and associated visibility reductions in the worded
forecasts north and west of a Lampasas to Bonham line overnight.

Carlaw

&&

.LONG TERM... /Issued 344 PM CDT Sat Sep 22 2018/
/Sunday through next Saturday/

A variable and somewhat unsettled weather pattern will persist
over the region from Sunday through the upcoming workweek.
Precipitation chances will remain in the picture - for parts of
North and Central Texas at least - for several of the upcoming
days. Confidence in the precise timing/location of new rainfall,
however, is not great at this time.

The persistent upper shortwave and accompanying surface low now
over our area will move into northeast Texas on Sunday, with a
mild northerly flow prevailing on the backside of these systems.
Skies will remain cloudy over the forecast area Sunday, and there
may be enough moisture and residual instability aloft to produce
a few showers over the eastern counties. The combination of weak
cold advection and clouds should inhibit daytime temperatures from
climbing out of the 70s anywhere except the far southeast
counties.

The upper level pattern will transition to a quasi-zonal or
southwesterly flow regime on Monday, and this will continue into
the midweek. At the surface, we`ll see winds shift around to a
southerly direction on Monday, accompanied by partial clearing.
Better insolation and higher thicknesses will facilitate a healthy
increase in afternoon temps Monday through Wednesday, with values
climbing well back back into the upper 80s and even some lower
90s. With plenty of residual surface moisture around and dewpoint
in the lower 70s, conditions will feel pretty stifling and un-
fall-like. Have held onto small PoPs for the easternmost counties
for Tuesday, where lingering isentropic lift and instability will
reside.

The Euro and GFS both depict another cold front diving southward
through our area by Wednesday afternoon. Both models swing a broad
upper shortwave eastward through the region in concert with this
frontal passage, and the resultant forcing for ascent seems
sufficient to justify chance PoPs areawide. Didn`t have a lot of
confidence in the timing/location of any convection that breaks
out along and ahead of the front, so pretty much broadbrushed the
PoPs during this time. Cold advection won`t be great behind the
front, but sufficient to reel highs Thursday back to near
climatological norms. Surface winds promptly swing back around to
the south by late Thursday and remain that direction into the
weekend.

The models diverge a bit in their depiction of the upper
level forcing mechanisms in the Friday/Saturday time period, but
the Euro (and to a lesser degree, GFS) generate a substantial
trough just upstream from North Texas by Saturday. In general,
warm, moist and unsettled conditions should exist at this end of
the forecast period, with scattered showers and thunderstorms
looking like a good bet.

Bradshaw

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    66  76  69  83  71 /  70  40  10  20   5
Waco                68  80  68  87  70 /  20  20  10  20   5
Paris               66  75  68  83  70 /  90  60  30  30  10
Denton              65  75  67  82  69 /  70  40  20  20   5
McKinney            67  75  68  82  70 /  90  40  20  20   5
Dallas              68  77  70  84  72 /  80  40  20  20  10
Terrell             70  79  70  85  71 /  90  40  20  20   5
Corsicana           70  80  70  86  71 /  30  30  20  20   5
Temple              66  79  68  85  70 /  10  20  10  20   5
Mineral Wells       64  75  66  83  67 /  50  30  10  10   5

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Sunday morning for TXZ093>095-104>107-
119>123-135.

&&

$$

82/08



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