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

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FXUS64 KFWD 031133 AAA

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
533 AM CST Sat Dec 3 2016

/12Z TAFs/

A very challenging and sloppy pattern as rains become more
widespread this morning and through early afternoon, before
tapering off off late this afternoon. Potential for TSRA in Central
Texas, along with cig/vsby trends will be relatively difficult
through tonight. An upper level disturbance is currently moving
northeast and toward the area early this morning. This will be our
first round of widespread rain. Cigs currently are IFR/LIFR across
Central Texas, while there`s a gradient of VFR to isolated IFR
across North-Central Texas.

.DFW Metro Airports...
Have decided to prevail low MVFR with VCSH through mid morning,
before more widespread light to moderate rain results in IFR cigs
with VSBYs ranging from IFR to low MVFR. As rain tapers off later
this afternoon, will continue to carry light SHRA with IFR to
possibly very low MVFR cigs. Tonight should be mostly dry, though
with conditions falling into IFR/LIFR with occasional drizzle or
sprinkles. Northeast winds 10-15 knots will become northerly
overnight at 10 knots or less.

.Waco Regional Airport...
Central Texas already now seeing the rain become widespread with
IFR/LIFR conditions prevailing through tonight. As weak subsidence
arrives later this afternoon (similar to DFW airports), the rain
will wane, but IFR/LIFR conditions will continue to prevail with
occasional drizzle or sprinkles. Like their neighbors to the
north, prevailing northeast winds 10-15 knots will become north 10
knots or less overnight.



.PREV DISCUSSION... /ISSUED 339 AM CST Sat Dec 3 2016/
Morning water vapor imagery shows that our upper low which will
bring several rounds of rain to the area has become cutoff and
continues to dig southeastward into northern Mexico. In addition,
a large plume of mid/upper level moisture can be seen
overspreading the region within a strong upper jet axis.
Increasingly diffluent flow aloft in advance of this upper low
will continue to support widespread rainfall across much of the
Southern Plains over the next 3 days.

Our first of 4 rounds of rain is departing to the northeast early
this morning, but our second wave is not far behind. A large swath
of showers and storms has developed across South/Central TX
overnight which will continue expanding northward over the next 12
hours. All of north and Central TX is expected to receive rainfall
today, especially throughout the morning hours. The development of
this rain swath is due to incredibly strong warm
advection/isentropic ascent above an inversion in the lowest
~200mb. Ascent is being aided due to our position beneath the
right entrance region of a 120kt 300mb jet located over the
Central Plains where strong upper-level divergence is occurring.
Elevated instability remains limited, and thunder becomes
increasingly unlikely the farther north your location. Have
restricted a mention of thunderstorms to along/south of I-20
throughout the day where at least a few hundred J/kg of MUCAPE is
available. The most intense rainfall is still expected to be
across our southeastern counties, roughly southeast of a Killeen
to Athens line; this area could receive in the neighborhood of
3-4" of rain through early this afternoon. At this time, do not
have much concern regarding flooding issues as antecedent
abnormally dry/drought conditions have been in place, so 3-4" of
rain over a 6-12 hr period should not pose much of a threat other
than some ponding in the typical low-lying areas. For these
reasons, and after inter-office collaboration, did not feel a
Flash Flood Watch was warranted in our forecast area. After this
batch of rain begins weakening and shifting to the east later this
afternoon (due to the strongest warm advection shifting to the
east), a lull in the rain activity should occur during the evening

Also of note for today, our high temperatures have already
occurred (at midnight) and will continue falling or remain nearly
steady in the mid 40s to around 50. Increasing east/northeast
winds at 10-15 mph coupled with cooling temperatures and
widespread rain will make for a nasty day for any outdoor
activities that may still be scheduled.

The third batch of rain should begin developing late tonight and
last into the early hours on Sunday morning. Most of this
activity will be across our Central TX counties where the better
moisture content will be located as a northern stream shortwave
swings through the area causing some weak ascent. Some parts of
North TX may actually remain dry during this time frame. As the
shortwave departs to the east Sunday morning, we may actually
become weakly subsident, and the plume of mid-level moisture
should start to shift east of the area. As a result, most of North
TX may actually be dry for most of Sunday while showers remain
possible across our far southern counties where an overrunning
setup remains in place in advance of the approaching cutoff low
moving northeastward out of Mexico.

The 4th and final wave of showers and thunderstorms will occur
late Sunday night through Monday as the upper low ejects
northeastward directly across our forecast area. A surface coastal
low is expected to develop across South TX as the low encounters
increased baroclinicity. This should be some of the strongest
forcing out of the entire event, and with cooling mid-level
temperatures, it should be the best chance for thunderstorms area-
wide rather than more stratiform rain. Have continued likely PoPs
area-wide on Monday with a mention of thunder as well. Depending
on the rainfall totals on Saturday/Sunday, we`ll need to keep an
eye on a low flooding potential for Monday`s activity as many
areas will now have saturated soils.

While the rain will come to an end Monday night, that doesn`t
mean we`re done with an active weather pattern. A shortwave will
drive a weak cold front into the area on Tuesday, so despite only
partly cloudy skies, temperatures will struggle to rebound to much
warmer than the mid 50s to low 60s due to weak cold advection.
This front will also keep the low-level moisture shunted to the
south of the area.

A much stronger front is still expected to sweep through the
region sometime Wednesday afternoon or Wednesday night, but models
still disagree on the timing at this point. Without much moisture
available, am not expecting much rain with this front, although
will keep a mention of showers east of I-35 in advance of the
front where some weak isentropic ascent and steep mid-level lapse
rates will be in place. Regardless of the cold front`s arrival
time, Thursday will be the coldest day of the season so far with
lows starting out mostly in the 20s and strong cold advection
keeping high temperatures in the upper 30s and low 40s during the
day. In addition, it will be quite windy with this front due to
strong surface pressure rises, and wind chill values in the teens
will be likely for some locations on Thursday morning. Cold
temperatures will continue through the end of the week with
surface high pressure continuing to build southward through the
Plains. Have undercut guidance on temperatures by a few degrees as
models generally struggle with the "extreme" temperature changes
and events that differ vastly from seasonal normals. A slight
warming trend should occur heading into next weekend.



Dallas-Ft. Worth    49  45  53  47  51 / 100  60  40  60  70
Waco                49  46  52  47  53 / 100  80  50  80  70
Paris               48  44  51  44  50 / 100  50  30  50  80
Denton              48  45  53  46  51 / 100  60  30  60  70
McKinney            48  45  53  46  50 / 100  60  30  60  70
Dallas              49  46  53  47  51 / 100  60  40  60  70
Terrell             49  46  53  47  52 / 100  60  40  70  70
Corsicana           49  46  53  47  52 / 100  80  50  80  70
Temple              49  46  51  47  54 / 100  80  60  80  70
Mineral Wells       48  45  54  45  52 / 100  60  40  60  70




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