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

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FXUS64 KFWD 232012

Area Forecast Discussion
National Weather Service Fort Worth TX
312 PM CDT Fri Jun 23 2017

/Tonight and Saturday/

Temperatures this afternoon have rocketed into the upper 90s to
near 100 degrees across the western 2/3rds of our CWA, with lower
to mid 90s showing up to the east. Dewpoint temperatures have been
hesitant to mix out so far, although we are seeing them slowly
fall into the lower 70s for the most part. The resulting heat
index values are an oppressively uncomfortable 100 to 110 degrees
at this hour, but these will fall below the century mark around or
shortly after 7 PM.

Regional surface observations, radar, and satellite data depict a
southeastward-advancing cold front which stretches from the Texas
Panhandle, northeast towards Frederick, Oklahoma, and just south
of Oklahoma City. Winds ahead of the actual cold front appear to
be steadily backing, which is effectively reducing the along-front
surface convergence. That said, velocity tensor plots show a
local max in convergence just north of the Red River, which is co-
located with a field of agitated cumulus and a previously robust
thunderstorm over Ardmore. With dewpoints in the low/mid 70s,
convective inhibition has all but eroded, with MLCAPE values
soaring towards 2000-3000 J/kg at this hour. As a result, we
expect additional isolated convection to gradually materialize
through the late afternoon hours mainly near the Red River, before
gradually slinking southward through the mid-late evening hours.
At this point, it appears any isolated thunderstorm activity would
most likely impact the DFW Metroplex towards the 7-10 PM
timeframe. Given DCAPE values well in excess of 1200 J/kg across
all of the region and 1000-700 mb theta-e deficits approaching 35
K, any storms that develop will have the potential to produce
severe-caliber downburst wind gusts this afternoon and evening.
There will also be a threat for 1" hail given the tremendous
instability in place, but a dearth of deep layer wind shear mean
very large hail is unlikely. The main area of concern for severe
storms during this period appears to be from near the I-20
corridor and points north to the Red River.

As these storms continue slowly southward, we may see a slow
downtrend in coverage and intensity with the loss of daytime
heating. Any respite will be short-lived, however, as an
additional disturbances begins to impinge upon the region from the
north. There is good model agreement that widespread (elevated)
showers and thunderstorms will develop late tonight (most likely
after midnight). Forecast soundings show dry air will linger,
which would support some degree of cold pool amalgamation
overnight/early Saturday morning as a loosely organized
thunderstorm complex gets going. The orientation of the low-level
flow would favor a southwestward motion overnight as this activity
surges towards Central Texas. With PWAT values approaching 2
inches (90th+ percentile for this time of year) and deep warm
cloud depths over 10 kft, locally heavy rainfall is possible
tonight, and this may cause result in localized flash flooding
especially along and north of I-20, and east of I-35/35W where
incipient storm motions should be slowest. Some of these storms
could also be strong, but the overall severe threat will dwindle
through the night.

This potential convective complex should be ongoing around
daybreak on Saturday, but it looks like overall precipitation
chances will steadily become confined to our Central Texas
counties through the day. While we can`t rule out some additional
storm development to the north later in the day, we may remain too
subsident to warrant anything more than 20-30% PoPs.



/Saturday night through Friday/

Both the mid level shortwave and slow-moving surface cold front
will be moving into Central and Southeast Texas as we move into
Saturday night. The cold front will likely lay up just southwest,
or along the Colorado River Basin over the northern Hill Country
the remainder of the weekend into Monday. Best rain chances are
expected to occur over the southwest half the region closer to the
surface front Sunday afternoon and evening, as another subtle
shortwave disturbance moves through weak, diffluent, mid level
flow during the prime heating part of the day. With relatively
weak wind shear and forcing aloft, along with weak convergence
near the old surface front, we only expect isolated-scattered
diurnal convective activity both Sunday and Monday afternoons. A
few stronger storms may occur late in the day over Central TX with
gusty winds, frequent lightning, and brief heavy downpours but
severe weather is not anticipated. It will be relatively cooler
however with our area north of the front and continued cloud cover
and spotty rainfall. Overnight lows through Monday will be 65-70
degrees with highs in the mid-upper 80s.

The upper high to our west will slowly strengthen and build east
toward I-35 mid-late week which will mean warming temperatures. In
addition, humidity values will increase once again with surface
winds backing to the south. Most areas except the far east will
see highs rise back into the 90s and combined with surface dew
point temperatures back up into the lower 70s, heat indices will
be on the rise again and future Heat Advisory issuances are not
out of the question for parts of the area.

There are signs of a weakness in mid levels of the atmosphere
over the northwest Gulf of Mexico late week that will result in
diurnal low convective chances each afternoon/early evening
Thursday and Friday across our far southeast counties. Otherwise,
a strong upper trough will shift east and move across the Central
and Northern Plains Friday Night into Saturday morning that will
fire a cluster of storms along a slow-moving surface cold front
draped from Northwest Texas/Oklahoma into the Midwest. This front
looks to stall just north and west of our area, however the
potential for a weakening MCS across areas north of I-20 is
certainly possible Friday Night and early Saturday. Being that
period is Day 8 of the forecast, we`ll keep rain chances
relatively low until models get a better handle on the overall
system and surface cold front later this week.



.AVIATION... /Issued 101 PM CDT Fri Jun 23 2017/
VFR conditions will prevail through the afternoon and early
evening hours at all TAF sites, with just FEW-SCT fair weather Cu
around FL040-060. Surface winds will continue to gradually back
around to the east-southeast and eventually east-northeast this
afternoon and evening ahead of an approaching cold front. For
brevity, opted simply to show a southeast wind in the Metroplex
TAFs this afternoon.

With so much moisture hanging out in the low-levels, relatively
weak convergence ahead of the aforementioned cold front may be
just enough to encourage some isolated thunderstorm development
this evening. Any storms that manage to develop would be capable
of producing strong to severe-caliber downburst wind gusts given
how warm and unstable the atmosphere will be. Much better
thunderstorm chances will then materialize overnight as subtle
forcing arrives behind the cold front, and have continued to
prevail TSRA at the Metroplex sites between 08-12z, and from
09-14z at Waco. There is still a good deal of uncertainty
regarding the timing of better thunderstorm chances, however, and
some adjustments to these time frames should be expected. As the
shallow frontal inversion saturates, low-MVFR cigs should
materialize at all TAF sites. There is also an outside shot at IFR
cigs towards daybreak and the mid-morning hours on Saturday, but
will let future shifts analyze this potential as short-term trends
become more apparent.



Dallas-Ft. Worth    73  82  71  86  71 /  70  70  20  20  20
Waco                74  86  71  87  70 /  50  60  30  30  30
Paris               69  81  66  84  65 /  70  60  20   5  10
Denton              69  80  68  85  68 /  70  60  20  10  20
McKinney            70  80  68  85  67 /  70  70  20  10  20
Dallas              73  82  71  87  71 /  70  70  20  20  20
Terrell             73  82  70  86  68 /  70  70  30  10  20
Corsicana           72  84  70  86  69 /  60  60  40  30  20
Temple              74  88  71  87  70 /  40  60  30  30  30
Mineral Wells       69  80  67  84  67 /  70  70  30  20  20


Heat Advisory until 7 PM CDT this evening for TXZ091>094-102>105-



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