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

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327
FXUS64 KFWD 150542
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1142 PM CST Sat Jan 14 2017

.AVIATION...
A stationary frontal boundary extended southeast of a KTYR
(Tyler) to KPSN (Palestine) to San Marcos (KHYI) line as of
15/05z (11 pm CST). This boundary is expected to start to slowly
lift northwest as a warm front during the day Sunday as a strong
upper level disturbance approaches. Expect mostly LIFR conditions
at all of the TAF sites tonight through midday (18Z) Sunday. As
the front lifts northward, we should see ceilings and visibilities
improve to IFR early Sunday afternoon and maybe to lower end MVFR
late afternoon. Northerly winds 5 to 9 knots will become
northeast by 12z Sunday and east by 15z and then southeast mid to
late afternoon.

Rainfall wise, areas of drizzle are expected through Sunday
morning. An organized area of showers and thunderstorms is
expected to move into the western cornerposts by early Sunday
afternoon and move east northeast to the I-35 corridor (this
includes the Metroplex and Waco TAF sites) mid to late afternoon
/22Z/. A second area (likely a line of thunderstorms) is expected
to approach the I-35 corridor after 03-04z Monday. Some strong to
severe storms will be possible.

58

&&

.UPDATE...
Widespread fog has become dense in several areas across North and
Central Texas on the north side of a stalled Arctic Front. The
front was located southeast of a line from Paris to Palestine to
Austin, and is not expected to lift north until Sunday.
Visibilities should begin to improve from southeast to northwest
mid to late Sunday morning, and should improve across just about
all of the region by early afternoon as southerly low level flow
increases in advance of an upper level storm system. The system
is still expected to bring good chances of showers and
thunderstorms Sunday afternoon and Sunday night. Otherwise, low
temperatures were adjusted downward tonight based on trends, and
the rest of the forecast looks good.

30

&&

.PREV DISCUSSION... /ISSUED 355 PM CST Sat Jan 14 2017/
The shallow cold airmass retains its grip on North Texas today
with temperatures in the 30s and 40s but changes are on the way
over the next 36 hours. The frontal boundary is currently still
located just south of our CWA border between Austin and San
Antonio then stretches sharply northeast to near Texarkana. It
appears to have actually drifted northwest into Anderson County
where temperatures at the Palestine RAWS site have climbed to 73
degrees over the last couple of hours. North of the front...a cold
cloudy day is in progress with areas of fog and drizzle. This is
expected to continue through the night with little temperature
change overnight. Lows will likely occur by midnight in many areas
with temperatures slowly climbing through the overnight hours.

Precipitation chances are generally low tonight with the exception
of the ongoing activity north of I-20 where the best moisture is
located. There is actually some mid level dry air that is moving
in from the east later this evening but this will be short lived
before strong moisture advection resumes tomorrow morning.

On Sunday...the powerful upper low will begin to eject
northeastward in response to an upstream shortwave. This will
induce pressure falls across much of the Southern Plains resulting
in increased low level winds. The stationary frontal boundary
will begin to retreat northward as a warm front through the day.
As the initial wave of strong isentropic upglide in the 290-300K
layer overspreads areas west of I-35 through midday...areas of
showers and a few thunderstorms are expected to develop. There are
some indications that this initial wave of convective activity
could be more expansive than previously thought so have increased
PoPs areawide by Sunday afternoon. By Sunday evening the
strongest forcing for ascent will begin to overspread North Texas.
With the warm sector expanding across North Texas and the
strength of the low level warm advection ongoing during this
time...it appears that there will be a little more instability to
work with into the evening hours.

There are two primary threats from tomorrow afternoon into the
nighttime hours across North Texas. The first will be the
potential for heavy rainfall. Strong moisture advection and the
potential for some localized training of cells could result in
some narrow swaths of heavy rainfall and localized flash flooding.
Given the overall progressive nature of the upper low and main
line of thunderstorms...we don`t see a need for a flash flood
watch at this time.

The other threat will the potential for some severe weather
including the possibility of a few tornadoes. It appears that
there will be anywhere between 500-1000 J/kg of CAPE from the most
unstable parcels through late Sunday evening...especially south of
I-20. Low level winds will be backed sufficiently ahead of the
surface trough to result in large clockwise curved hodographs
through late evening. While some of the instability is likely the
result of steepening lapse rates aloft with the approach of the
upper trough...the environment will be favorable for QLCS
tornadoes within the strongly forced line of convection or
isolated tornadoes with any robust convection in the warm sector
ahead of the main line. We still think the lack of more low level
instability will be the main limiting factor to a more widespread
severe weather threat. Again...this potential will be monitored
closely through the day as the environment can change rather
quickly.

By late tomorrow night...the main line of storms will push to the
east of the area with a weak front sliding into the region. This
should push the bulk of the precipitation out of the area. The
ECMWF and GFS handle another upstream shortwave differently
through mid-week which results in low confidence in the forecast
Tuesday through Thursday. Will keep some low PoPs in during this
time.

Dunn



&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    42  64  54  67  44 /  20  60 100  10  10
Waco                46  68  57  68  46 /  20  70 100  20  20
Paris               47  65  58  66  45 /  20  20 100  50  10
Denton              40  62  50  65  39 /  20  70 100  10   5
McKinney            42  64  54  66  42 /  20  50 100  20   5
Dallas              43  65  56  67  45 /  20  60 100  20  10
Terrell             47  69  57  68  46 /  20  40 100  30  10
Corsicana           48  69  59  70  49 /  20  40 100  40  20
Temple              45  69  57  68  48 /  20  70  90  30  30
Mineral Wells       39  61  46  65  39 /  30  70 100   5   5

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until noon CST Sunday for TXZ092>094-102>105-
116>121-129>134-141>146-156>161.

&&

$$

58/30



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