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

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FXUS64 KFWD 240519 AAC
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1219 AM CDT Sat Jun 24 2017


.AVIATION...
/06Z TAFs/

Overall, no significant changes were needed for the DFW TAF, but
the timing of storms at KACT needed to be pushed back in time.

For the DFW Metroplex: A line of storms along the southward moving
outflow boundary/front is about to move into the northern portions
of the Metroplex. Gusty winds near 25 kts and lightning are the
main threats with this activity. Additional and more widespread
showers and storms are expected overnight, continuing through most
of Saturday morning. MVFR cigs will likely develop near daybreak
and also persist for much of the morning hours. Additional MVFR
cigs may occur Sunday morning, just beyond the extended portion of
the DFW TAF. Northeast winds are expected through most of the TAF
period.

KACT airport: VFR conditions will prevail through the night and
then convection should occur in the area for a good part of
Saturday. However, we will have to monitor radar trends
overnight, as convection may occur as early as 09Z if an outflow
boundary in East Texas progresses as far west as Waco. MVFR cigs
are expected to occur in the late morning through mid afternoon
hours, and may also quickly redevelop late Saturday night. South
winds ahead of the cold front will become northeasterly behind it
and remain northeasterly through the end of the TAF period.

JLDunn

&&


.UPDATE... /Issued 1004 PM CDT Fri Jun 23 2017/
The leading edge of the outflow boundary/front is moving south
through our northern counties along the Red River. This activity
will likely persist for at least a few more hours with a threat
for strong and severe storms. Additional development of more
widespread activity is still expected overnight, but our southern
counties may be spared until after 7 am in the morning. Main
adjustment for the update was to lower (but not completely remove)
PoPs across our Central Texas counties overnight.

JLDunn

&&

.SHORT TERM... /Issued 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.

Carlaw

&&

.LONG TERM... /Issued 312 PM CDT Fri Jun 23 2017/
/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.

05/

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    72  83  71  85  68 /  70  60  20  30  10
Waco                76  87  72  86  70 /  40  70  30  40  20
Paris               71  81  66  83  64 /  70  50  20  10  10
Denton              70  81  68  84  67 /  70  60  20  30  10
McKinney            71  81  68  84  66 /  70  60  20  20  10
Dallas              73  83  71  86  70 /  70  60  20  30  10
Terrell             74  82  70  85  67 /  70  60  20  30  10
Corsicana           75  85  70  85  68 /  50  70  30  40  20
Temple              77  88  71  86  70 /  30  60  40  50  30
Mineral Wells       70  82  67  83  66 /  70  60  20  40  20

&&

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

$$

82/24



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