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

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FXUS64 KFWD 220436 AAD
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1136 PM CDT Tue Mar 21 2017

.AVIATION...
Expect low clouds to form over South Texas and spread north into
Central and North Texas overnight on a 40-knot southerly low level
jet. Expect IFR ceilings to move into Waco 08-09z and into the
Metroplex 11-12z. Ceilings are expected to rise into the MVFR
category around 16z and VFR conditions are expected 19-21z.
Southerly winds at 10 to 15 knots will prevail and some gusts to
20 knots will be possible during the day Wednesday. Some MVFR
ceilings should work their way back into North and Central Texas
overnight Wednesday night so have included BKN015 in the extended
portion of the DFW TAF starting at 09z Thursday.


58

&&

.UPDATE...
/1034 PM CDT Tue Mar 21 2017/
Isolated showers and thunderstorms over Eastland county refuse to
die and a couple of new showers have popped up along an outflow
boundary in the last half hour. Have sent a quick update to
expand the isolated shower/thunderstorm area to include locales as
far east as Comanche to just northwest of Stephenville through 2
AM.

&&


.SYNOPSIS...
Above normal warmth is forecast to continue through a majority of
the outlook period with a low potential for some rain over the
next 1-2 days. Thursday should be mostly dry with increasing rain
chances on Friday and perhaps early Saturday. Most of the day on
Saturday appears dry at this time, with increasing shower and
storm potential late Sunday. Next week will likely remain active
with very progressive flow.

&&

.SHORT TERM (Tonight through Thursday)...
Surface analysis this afternoon revealed a diffuse frontal
boundary near a Lubbock to Childress to Oklahoma City line
continued to slowly sag southward. An ill-defined dryline was also
noted down across the Permian Basin of west TX. Satellite imagery
continues to show some pockets of ACCAS to the west and I`ll
maintain a very low potential for showers and an isolated
thunderstorm or two mainly for portions of the Big Country and
western parts of Central TX. Further north, the cold front will
likely slip to the south of the Red River late tonight into early
Wednesday morning.

While model QPF suggests a chance for rain along the Red River,
forecast soundings are very unimpressive with regards to
precipitation potential. A few showers and a lone storm have
developed across southern Oklahoma and given these observations,
I`ll carry a 15-20 PoP along the Red River through the evening
hours. I`ll also go ahead and include in a mention for some
patchy fog as a reservoir of low level moisture INVOF the front
coupled with light winds will facilitate the development of some
patchy fog. Winds across eastern and southeast zones will also
likely decrease and with low dewpoint depressions, I`ll also
include a mention of patchy drizzle/fog here as well. Overnight
low temperatures across most areas will remain above normal with
readings in the 50s and 60s.

Wednesday will be warm and humid as the frontal boundary becomes
very diffuse across North TX. With dewpoints in the low to mid 60s
and likely a thick blanket of clouds across the region, the
diurnal temperature curve won`t be as steep as we`ve experienced
across the area. Afternoon high temperatures will still remain
above normal values with most areas in the 70s and 80s. Areas
across northeast zones (near Paris and Bonham) may remain
entrenched in cloud cover for most of the day and so temperatures
here may remain in the 70s. Little to no precipitation is expected
on Wednesday as the spine of the mid and upper level ridge axis
becomes oriented directly across North and Central TX. Wednesday
night into Thursday morning should feature additional overnight
warmth as a slightly better fetch of low level moisture continues
to lift northward. This will be in response to a deepening upper
trough that will start to slide eastward across the Pacific
Southwest. Surface overnight low temperatures Wednesday evening into
Thursday morning should remain on the high side with most areas
in the upper 50s to low 60s. A few of the urban areas may remain
even warmer with overnight low temperatures in the mid 60s. The
fog potential Wednesday night into Thursday morning looks a little
lower than tonight as wind speeds will be a tad higher which will
promote more nocturnal mixing. There should be a large area of
stratus across the area, however.

Thursday is expected to remain dry and warm as the ridge remains
in place across the region. With the approach of the upper trough,
deeper lee-side cyclogenesis will ensue. This will tighten the
surface pressure gradient which will allow winds to howl upwards
towards the 20 to 25 MPH range, especially out across western
zones. Winds may gust to the 30 to 35 MPH range and a small Wind
Advisory may be necessary out across western zones. Low level
moisture combined with increasing green vegetation, per NDVI
satellite derived products, should be enough to hamper a
widespread fire weather threat. That being said, the breezy
conditions coupled with above normal temperatures may still
promote rapid fire growth. Daytime high temperatures should climb
into the 80s region wide. I went ahead and nudged temperatures
above guidance as the tight pressure gradient will assist in low
level mixing which may warrant a bit more in the way of sunshine
than models indicate. Thursday evening into Thursday night should
be mostly dry as forcing for ascent slowly arrives from the west.

&&

.LONG TERM (Thursday through Sunday)...
Overnight low temperatures on Friday will be dependent on the
coverage of convection. For now, I trended with lower temperatures
near and west of I-35 as the potential for showers and storms
will be highest on Friday morning. Temperatures near and west of
I-35 will be in the upper 50s to near 60 degrees. Areas further
to the east will will remain mild with morning temperatures in the
low to mid 60s.

The latest model guidance remains consistent with the timing of
the upper trough that is forecast to move out of the four corners
region. With a strong mid/upper level jet (on the order of 100-110
knots), good DPVA and decent height falls, forcing for ascent
should not be in short supply. Furthermore, forecast soundings
indicate little in the way of inhibition will exist which should
result in widespread showers and thunderstorms. Right now, the
best chance for showers and storms near and after midnight will be
out across western zones near the Highway 281 corridor. Closer
towards sunrise, showers and thunderstorms will likely continue to
develop and move eastward towards the I-35 corridor. Friday
afternoon and evening, showers and storms are likely across east
TX. With regards to the severe weather potential, there are still
some uncertainties concerning the overall probabilities. For
areas along and west of the I-35 corridor, showers and storms in
the morning time will likely yield a lower severe weather
potential as a large reservoir of instability isn`t likely to
sustain persistent updrafts. That in mind, any updrafts that can
efficiently utilize any available instability will be juxtaposed
with sufficient deep layer shear values on the order of 40 to 50
knots which would be more than adequate for organized convective
modes. The most likely mode, given that the deep layer shear
vector is oriented parallel to the Pacific Front/Dryline, would be
a squall line.

Showers and thunderstorms will continue to progress east of the
I-35 corridor through the afternoon hours. While there will be a
buildup of instability ahead of this line, there`s likely to be a
large quantity of cloud cover which would limit diabatic heating`s
contribution to the generation of instability. That being said,
we will have to keep a close eye on this as models do develop a
small and narrow corridor of higher instability. As noted above,
there will be sufficient deep layer shear in place to promote
organized storm modes (which would more than likely be in the form
of a squall line). Models don`t completely scour out this low
level moisture and this will be important for Sunday`s rain/severe
weather chances.

Bottom Line for Friday: The severe potential at this time will
likely be greatest east of the I-35 corridor and the main hazard
will be damaging straight line winds (should severe storms occur).
In addition there will be a fire weather threat on Friday in the
wake of storms. See the fire weather discussion below.

Saturday should be a nice, but breezy day with generally
northwest to westerly winds and warm conditions. As mentioned
above, this should result in good downslope warming which will
continue to support above normal temperatures with readings in the
upper 70s and 80s and a fire weather threat.

The most noteworthy changes to the forecast were in the Sunday
time frame where models signal a potential for additional
precipitation. The general model consensus shows a fast moving
upper trough slicing eastward through the southern stream flow
through the day on Sunday. A stout mid-level low will slide into
the TX/OK panhandles with a surface dryline trailing southward
through the Big Country. The upper level jet is only around 70-80
knots in most model progs, but the low level moisture return
appears quite impressive. Models generally agree, that around
1500-2000 J/kg of instability will be in place with around 50
knots of deep layer shear. Forecast soundings indicate a cap will
likely keep any precipitation suppressed until late Sunday. With
heating and forcing from the upper trough, the cap should weaken
and it`s likely that isolated to scattered showers and
thunderstorms will erupt near and east of the Highway 281
corridor. Given the aformentioned shear and instability
parameters, organized convective modes appear possible yet again,
with a greater potential for a supercellular mode on Sunday
(compared to Friday), given the orientation of deep layer shear to
the dryline. We will keep close tabs on this as this appears to
be a slightly more recent development in the latest model
guidance.

The active weather pattern will continue into next week with
additional rain chances. Despite this, above normal temperatures
will likely continue.

24-Bain

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    63  84  64  84  61 /   5   5   5   5  20
Waco                62  84  64  85  61 /   5   5   5   5  20
Paris               61  73  58  83  59 /  10  20  10  10  10
Denton              61  81  63  84  61 /   5   5   5   5  20
McKinney            62  82  62  84  61 /  10  10   5   5  20
Dallas              64  84  64  84  62 /   5   5   5   5  20
Terrell             63  80  62  84  63 /   5   5   5   5  20
Corsicana           62  83  63  85  62 /   5   5   5   5  10
Temple              61  83  64  86  61 /   5   5   5   5  20
Mineral Wells       61  83  62  85  60 /   5   5   5   0  40

&&

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

$$

58


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