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FXUS64 KFWD 211354
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
754 AM CST Wed Feb 21 2018


.MESOSCALE UPDATE...
...Upgrade to an Ice Storm Warning north and west of a Cisco to
Bowie line today...

The overnight/early-morning round of showers and embedded
thunderstorms is just now beginning to lift north and east of the
region as the associated jetstreak is moving into Oklahoma. This
initial wave has generally resulting in minor ice accumulations on
elevated surfaces across our northwest where it's coldest, but
overall impacts on roadways have been minimal for the most part
thus far. However, the next vort max which earlier moved off the
high terrain of Mexico has resulted in the development of new
precipitation which is spreading across the Concho Valley/Rolling
Plains. Forecast soundings reveal gradually steepening mid-level
lapse rates associated with the dynamic cooling from the
approaching disturbance with MUCAPE values forecast to increase to
around 500-800 J/kg through the morning hours.

As a result, this next round of precipitation is expected to be
more convective in nature as evidenced by the increased lightning
and cooling cloud tops out west. With all of this in mind, we have
elected to issue an Ice Storm Warning for our far northwestern
counties (Eastland, Stephens, Palo Pinto, Young, Jack, and
Montague) after collaboration with WFO San Angelo with
indications of impacts quickly ramping up in the Concho Valley due
to this convective freezing rain and sleet mix. This warning has
been relegated to the counties where the coldest air is forecast
to be in place (under 28 degrees) through the morning and
afternoon hours. For simplicity, we will let the Ice Storm Warning
ride through midnight tonight to avoid having to overlap an
additional winter weather advisory, although the most significant
icing potential should be over by the mid-evening hours.

Carlaw

&&


.AVIATION... /Issued 610 AM CST Wed Feb 21 2018/
IFR conditions are expected to prevail today and and
ceilings may fall into the LIFR category tonight. A large band of
rain will be moving across the region through 16z. As another
upper level disturbance approaches this afternoon, another round
of rain, possibly with some isolated thunderstorms, is expected
afternoon. Temperatures are key to this forecast as KAFW has
already fallen to 32F. KFTW may fall to 31F this morning and KDFW,
KDAL and KGKY are expected to bottom out just above freezing.
Needless to say, we will continue to monitor temperature trends
and make adjustments to the precipitation type if needed.

Temperatures are forecast to be in the lower to middle 30s this
afternoon and tonight but may fall below 32F at KAFW and KFTW
09-11z Thursday.


At Waco, overall similar trends are expected but temperatures will
easily remain above freezing through 12z Thursday.

58

&&

.SHORT TERM... /Issued 354 AM CST Wed Feb 21 2018/
/Today and Tonight/

The combination of increasing upper-level diffluence in
association with the right entrance region of an upper-level jet
streak and yet another shortwave moving out of Coahuila, Mexico is
resulting in the development of our next wave of precipitation.
Recent hi-res guidance seems to be catching onto most of this
activity pretty well, which lends confidence to PoPs in the
short-term which will be near 90-100 percent for much of the
region. Temperatures are obviously one of the more important
aspects of the short-term forecast. As of 3 AM, the freeze line
extended from near a Bonham to Decatur to Mineral Wells to
Comanche line. Any precipitation north and west of here is falling
as a mixture of rain and freezing rain. A combination of the
colder NAM guidance and the GFS LAMP data actually seemed to be
doing a respectable job with regards to temperatures, and this
guidance was generally used to depict temperatures today and
tonight. With lingering gusty north winds in the wake of
yesterday's front and temperatures north of the Red River hanging
out in the mid and upper 20s, cold advection will persist through
the morning and into the afternoon hours across the region
allowing temperatures to slowly fall across the western 2/3rds of
the area.

This current batch of showers and embedded thunderstorms will
persist into the mid-morning hours before gradually peeling away
to the east. Up along the Red River, we elected to add Fannin
county to the winter weather advisory for this morning activity
with temperatures falling to around 30. Locales from near Bonham
to McKinney to Dallas and points eastward should actually slowly
warm during the afternoon, however, as surface winds become more
easterly.

Our far north and western counties continue to be where our
highest concern is for icing issues, as this is where the
combination of the coldest temperatures (falling into the upper
20s) and an additional wave of possibly convective precipitation
develops during the late-morning and early-afternoon. Here,
roughly west of a Cisco to Gainesville line, some ice
accumulations of one to two tenths of an inch can be anticipated,
creating for treacherous travel today.

The immediate Metroplex posed the next conundrum. While it seems
likely that outlying spots across parts of Tarrant County will
fall to below freezing this morning (the Alliance and Azle areas,
for example), guidance supports mainly 31-32 degree readings here,
which should help curtail any significant icing issues.
Regardless, some elevated roadways may become slick, and a glazing
on trees is possible here. Basically, the message here is that
while freezing rain is technically occurring at 32 degrees, it
typically takes several hours at 29-30 or so to start causing
substantial issues. Either way, take it slow this morning where
temperatures have fallen to 31-32.

It's looking like the most widespread/heaviest precipitation will
clear the region by early this evening, but we may have to contend
with very light showers/drizzle as the low-level remain quite
moist. For this reason, the winter weather advisory was extended
through midnight tonight to account for any lingering issues.

Otherwise, locally heavy rainfall will persist today, and with
yesterday's soaking rainfall, it won't take a lot of additional
precipitation to cause some runoff issues.

Carlaw

&&

.LONG TERM... /Issued 354 AM CST Wed Feb 21 2018/
/Thursday through Tuesday/

After a brief respite overnight Wednesday night, another
shortwave is expected to approach Thursday. With temperatures
expected to be 28 to 32 degrees around daybreak Thursday along and
northwest of a Goldthwaite to Glen Rose to Sherman line, have
included a mention of freezing rain or rain/freezing rain in those
areas. Temperatures should rise above freezing by midday and have
just gone with a chance of showers area wide with isolated
thunderstorms from Lampasas to Gainesville line. Highs Thursday
will range from the upper 30s northwest to near 50 southeast.

An unsettled weather pattern will continue into Saturday with
good chances of showers and thunderstorms. Fortunately, as a
surface ridge moves east, winds will come around to the east and
southeast Friday and to the south Friday night. This will result
in a warm-up. Temperatures Thursday night will be nearly steady in
the mid 30s northwest to around 50 southeast. A warm front will
lift northward during the day Friday. Highs will range from the
lower 50s northwest to the lower 70s southeast. As a shortwave
moves out of the Rockies Saturday, a cold front will sweep through
the region, bringing drier air and a temporary end to the rain by
Saturday night. Dry weather is then expected through Monday. An
approaching shortwave will bring chances of showers and
thunderstorms to the region again overnight Monday night into
Tuesday. Temperatures should be near to slightly above normal
Sunday through Tuesday.

58

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth 35 33 40 40 61 / 100 40 70 70 80
Waco 38 34 43 43 66 / 100 40 70 70 70
Paris 44 38 50 48 64 / 100 60 80 90 80
Denton 33 32 39 39 57 / 90 40 60 70 80
McKinney 35 33 43 41 61 / 100 50 70 70 80
Dallas 35 34 42 42 63 / 100 40 70 70 80
Terrell 42 35 47 46 66 / 100 60 80 80 80
Corsicana 42 35 46 46 67 / 100 60 80 80 70
Temple 40 34 44 44 67 / 100 40 70 70 60
Mineral Wells 31 31 39 39 56 / 80 30 50 60 80

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Flood Watch through this evening for TXZ092>095-102>107-116>123-
130>135-143>148-157>162-174-175.

Winter Weather Advisory until midnight CST tonight for
TXZ092>094-102-103-117-130>132-141.

Ice Storm Warning until midnight CST tonight for TXZ091-100-101-
115-116-129.

&&

$$

90/58
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