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

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FXUS64 KFWD 171823 AAB

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1223 PM CST Tue Jan 17 2017

/18Z TAFs/

Several challenges will exist throughout the 24-30 hour period of
the TAFs, including timing of rain, potential for thunder, and
cig trends after 00Z Wed.

Currently, VFR conditions will continue at DFW sites with an
increase of showers through early evening, as a strong shortwave
trough out west approaches the area. MUCAPE values are higher at
Waco with up to 250 J/KG versus less than a 100 J/KG here at DFW.
They`ve already had a few lightning strikes at Waco today and
feel as the shortwave trough approaches, lapse rates aloft should
steepen across all terminals with some marginal MUCAPE aloft. Will
carry VCTS at Waco from now through 09Z, while delaying the start
of VCTS at D/FW Metro terminals until this evening and lasting
through daybreak Wednesday.

Cigs should continue to come down beginning late today, but
especially tonight into Thursday morning, as isentropic ascent
increases in the lower levels and rainfall becomes more widespread.
Look for MVFR cigs to arrive by mid evening, then likely falling
into IFR at all airports after midnight. There may even be some
TEMPO LIFR at times during the pre-dawn through mid morning hours,
in between bouts of more sustained rainfall. Look for adjustments
to be made in successive TAF sets, as details become more clear.

Otherwise, north flow will persist at all terminals around or less
than 10 knots, including Waco. The warm sector will remained
confined closer to the TX coastline and across South TX, where an
inverted surface trough will be situated.



.PREV DISCUSSION... /ISSUED 406 AM CST Tue Jan 17 2017/
An active weather pattern will continue for the next 7-10 days
with several chances for rain. Temperatures will remain above
normal, and there are no signs at this time that another
intrusion of arctic air is in store for at least the next 7-8

The next in a series of upper level disturbances that will move
through the Plains is currently located over Baja California. The
upper level low will dig a little further south this morning, and
then start moving northeast into New Mexico later today and
tonight. Isentropic lift ahead of this disturbance is already
generating showers this morning across our southern and eastern
counties with light rainfall accumulations. Showers and isolated
thunderstorms will slowly spread north today, mainly this
afternoon, as the upper level low starts to move northeast and
warm air advection and isentropic lift increase atop the shallow
cool layer at the surface in the wake of a cold front that moved
through yesterday. Numerous showers and thunderstorms are expected
tonight as the upper level low moves closer to the Southern
Plains, and model guidance suggests some heavy rainfall will be
possible which may result in some flood issues.

Much of the region was already saturated with 1-3 inches of
rainfall Sunday evening, and we know or suspect standing water
remains in many places, including our far southeast counties and
likely along the track of the lone supercell from Coryell County
into the DFW Metroplex. Showers and thunderstorms tonight are
expected to be efficient rainfall producers, but will also be
moving at a decent speed that may help to prevent widespread flood
issues. However, we will have to monitor for training of storms
that may result in localized flood issues. The best potential for
heavy rainfall will be in our southeastern counties where hi-res
and ensemble guidance indicate heavy showers and thunderstorms
will occur between roughly 3 am and 9 am. Another 1-2 inches of
rain appears possible tonight into Wednesday morning, especially
in our southeastern counties. At this time, we do not plan to
issue any flood headlines, but will pass onto the next forecast
shift(s) the need to watch the trends.

The rain will shift east on Wednesday as the upper level low pulls
north of the region, and the best lift moves to the east. It will
still be rainy across roughly the eastern half of the CWA
Wednesday morning but most of the rain should clear out by
afternoon. The exception to this will be in our southeastern
counties where weak isentropic/warm air advection lift will
continue and scattered showers will be possible through Wednesday
night. As one more upper level trough pivots around the previous
upper level low, and through the Southern Plains on Thursday,
there may be enough moisture still in our eastern counties for a
few showers east of Interstate 35.

The weather is expected to be quiet and warm on Friday with upper
level ridging moving overhead and south winds already in place at
the surface. Confidence in the forecast beyond Friday is still
low at this time due to differences between the models so kept
PoPs on the lower end for now. Another strong upper level trough
will dig across the western CONUS Friday and Saturday, quickly
moving across the Southern Plains Saturday night into Sunday.
Another round of rain is possible this weekend, ahead of this
system. Right now, it does not appear there is much of a severe
weather threat, but we will need to keep an eye on this as the
set-up has the potential to produce a severe weather event. The
lift is definitely strong enough, the wind shear looks decent, and
there may be sufficient moisture in place. SPC is already
highlighting an area to our east out ahead of this system.

The upper level trough quickly wraps up into a closed low over the
Southern Plains and gives us a shot of cold rain on the backside
of the upper level low during the day on Sunday, in particular
across our northern and northeastern counties. The H850 and above
temperatures are very cold, and at first glance could suggest
wrap around snow, but sounding analysis indicates the layer below
H850 is significantly warm enough and moist enough to melt any
snow that may fall from a higher level. Wet bulb temperatures are
also forecast to remain well enough above freezing, but again
this small detail may be another thing to keep an eye on.



Dallas-Ft. Worth    46  56  45  69  48 /  90  40  10  10   0
Waco                45  58  44  71  48 /  90  50  20  10   0
Paris               45  54  47  64  48 / 100  60  20  20  10
Denton              42  56  41  68  46 /  90  20  10   5   0
McKinney            43  56  43  67  46 /  90  40  10  10   5
Dallas              46  57  47  69  49 /  90  40  10  10   0
Terrell             46  57  47  68  48 / 100  60  20  20   5
Corsicana           48  58  48  69  50 / 100  80  30  20   0
Temple              46  58  46  71  49 / 100  50  30  10   0
Mineral Wells       42  57  43  71  45 /  90  10  10   5   0




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