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

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FXUS64 KFWD 131802
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1202 PM CST Fri Jan 13 2017

.UPDATE...
No major changes to the current forecast. The initial wave of
strong isentropic ascent over the surface cold front has resulted
in a large batch of light rain that continues to spread north
through the region. Most of the activity is along and just west of
the I-35 corridor and will spread north to the Red River through
early afternoon. The surface front is across our extreme southern
counties just south of Killeen to just north of Hearne then
stretches northeast to north of Athens. There is a substantial
temperature difference across the boundary with temperatures in
the 70s at Palestine and Athens and 40s and 50s north of the
boundary. The front is unlikely to move much over the next 12
hours so high temperatures near the boundary will be highly
dependent on short term mesoscale boundary motion.

Only changes through the short term were to bump up PoPs through
the evening where rain is ongoing and made minor tweaks to hourly
temperatures.

Dunn

&&

.AVIATION...
/ISSUED 537 AM CST Fri Jan 13 2017/
/12Z TAFs/

Concerns...IFR and MVFR conditions through the period.

Generally poor flying conditions are expected across the region
this weekend. MVFR cigs with bases less than 2 kft are already in
place at all the TAF airports. Conditions are expected to
deteriorate into IFR category by mid-morning with scattered areas
of drizzle and showers streaming north across the region.

Metroplex airports--IFR conditions are expected to prevail
for most of the valid TAF period. A brief period of low-end MVFR
cigs is possible this afternoon and/or evening but guidance is in
pretty good agreement that warm air advection over the shallow
surface front will keep IFR conditions in place. The best time
period for scattered drizzle and showers to move through the
airports is through the early evening hours, but some
precipitation activity is also possible overnight. North winds
will prevail through the period.

Waco airport--The Waco airport currently is and will remain very
close to a stalled front just to its south and southeast. Guidance
varies considerably on if the front will lift a little north
today. For now, will keep a pessimistic TAF with IFR conditions
through nearly all of the valid period. However, if the front
drifts north at all, MVFR or even VFR conditions may occur,
resulting in a drastic change to the TAF. Even if IFR conditions
continue during the day today, a brief period of low-end MVFR cigs
is possible this afternoon and/or evening, but IFR conditions
will quickly return overnight. Assuming the front stays south of
the airport, north to northeast winds will prevail, but could
become east or southeast if the front drifts north. The best time
period for scattered drizzle and showers to move over the airport
is through the early evening hours, but some precipitation
activity is also possible overnight.

JLDunn


&&



.PREV DISCUSSION... /ISSUED 404 AM CST Fri Jan 13 2017/
A challenging forecast is in store for the next few days. We`ll be
dealing mostly with nuisance showers today and Sunday as a cold
front remains stalled through the area. While temperatures are
fairly cold in parts of North TX, they are expected to remain
above freezing throughout this time and the winter weather
potential will remain well to the north of our area. The main
forecast concern continues to be Sunday and Monday when some
strong/severe storms are possible as well as heavy rain and
flooding.

Models have had a difficult time handling the shallow cold front
which is now stalled through Central TX. While the front dove
farther south than initially expected, the potential for any
frozen precip continues to be displaced well to the north of our
area where the subfreezing surface air will continue to be
located. This front is incredibly shallow and the 925mb flow
remains out of the south as warm moist air overruns the Arctic
surface air. Warm advection in the 925-850mb layer is increasing
this morning which is why rain showers are beginning to develop
across the region. This trend will continue through the morning
hours, although rain is expected to remain light. Have left a
mention of isolated thunderstorms with latest analyses showing a
few hundred J/kg of MUCAPE, but most of this instability is above
an inversion located around 750mb so showers won`t really be able
to harness this buoyancy. Showers should increase in coverage
this afternoon, especially across parts of North TX where warm
advection will be the strongest.

The temperature forecast today has a significant bust potential
depending on how the front becomes situated. Temperatures near
the boundary could easily be 10 degrees warmer/cooler depending on
if the front wavers slightly farther north/south. Have continued
to stick closely to the high-res guidance including the NAM, HRRR,
and RAP as they`re the only models that have a decent handle on
the current environment. The front should remain stalled across
Central TX into tonight and Saturday as warm advection showers and
drizzle continue across parts of the area. Our far northwestern
counties will be the coldest on Saturday morning but should still
remain above freezing, thus we shouldn`t have to worry about
frozen/freezing precip.

By late Saturday, the upper low currently diving south along the
west coast will be approaching TX from the west. As it does, the
stalled front should begin to lift back to the north as a warm
front Saturday afternoon and evening. While I`ve relied heavily on
the NAM for the first portion of the forecast, have opted for the
slightly faster GFS and ECMWF solutions regarding the front`s
northward retreat as both of these models are slightly faster with
the position of the upper low. Saturday`s temperature forecast
could also bust if the slower NAM solution ends up being correct
as temperatures north of the front would still struggle to make
it out of the 40s and 50s Saturday afternoon. If the front does
lift north toward the Red River, temperatures will be in the 60s
and 70s for most locations.

The main window we continue to watch is Sunday and Monday which is
when we`ll be impacted by the upper low. It will take on a
negative tilt as it swings northeastward through West TX resulting
in diffluent flow aloft accompanied by the advection of a strong
vort max. Strong lift will cause storms to develop mostly across
West TX on Sunday which will move east into North and Central
Texas beginning Sunday afternoon. A low potential for
strong/severe storms will exist mostly for areas along/west of
I-35 late Sunday as strong forcing and ample shear will be in
place. The limiting factor is instability, which is typical for
this time of year, but 500-800 J/kg of SBCAPE in the warm sector
south of the northward-moving warm front will be sufficient for a
strong or marginally severe storm. The SHERB parameter for high
shear and low buoyancy is keying in on this potential with values
over 1.0 across our western areas Sunday evening/night. Winds
should be the primary threat as 50+ kts will already be in place
through the low-levels and it won`t take much to mix this
momentum down to the surface. Widely curved hodographs will
certainly be sufficient for rotating storms as well, but again,
the lack of low level instability should keep a tornado threat
very low. Any line or cluster of storms that moves into the area
will be capable of producing heavy rain and localized flooding
given the anomalously high PW values which will be around 3SD
above normal. Activity will likely be slow to push eastward which
could result in some north-south oriented cell training.

Widespread rain/storms should continue into Monday while
continuing to shift eastward. Another strong/severe storm threat
may exist across our southeastern areas on Monday afternoon where
dewpoints in the mid 60s and temperatures in the 70s will yield
more favorable surface based instability. However, the stronger
lift that was responsible for the initial storms will be lifting
off to the northeast at this time which may inhibit the strength
of storms. The upper low`s associated surface low will also be
carried off to the northeast which will cause a cold front to be
pulled through the area Monday night and Tuesday. Some additional
showers are possible along this front through the day Tuesday but
the ingredients for storms, especially strong storms, should have
shifted out of the area by this time.

Have left a dry forecast for the remainder of the week as moisture
will be scoured out. A pair of vigorous shortwaves will pivot
through the Southern and Central Plains during this time but it
appears all of the moisture will be displaced to our east, leaving
us with mostly dry conditions and near-normal temperatures.

-Stalley



&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    50  46  63  51  66 /  60  40  40  20  40
Waco                63  51  67  56  71 /  60  30  30  20  40
Paris               55  51  63  54  66 /  50  40  40  20  20
Denton              48  43  57  49  65 /  60  40  40  20  40
McKinney            50  45  61  51  65 /  50  40  40  20  30
Dallas              52  47  64  52  66 /  60  40  40  20  40
Terrell             60  51  67  54  67 /  40  40  30  20  30
Corsicana           66  54  71  54  70 /  30  30  20  20  30
Temple              71  53  70  57  71 /  50  30  30  20  40
Mineral Wells       45  41  57  49  66 /  60  40  50  20  50

&&

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

$$



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