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

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FXUS64 KFWD 141135
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
535 AM CST Thu Dec 14 2017


.AVIATION...
/12z TAFs/

North winds will prevail through the valid TAF period, with a
period of breezy and occasionally gusty winds later this morning
and into the afternoon. VFR conditions are expected with
occasional mid and high cloud cover invading the skies over the
Metroplex, with a more continuous SCT-BKN deck farther to the
south near the Waco TAF site.

Carlaw

&&


.SHORT TERM... /Issued 315 AM CST Thu Dec 14 2017/
/Today and Tonight/

A cold front is working its way through the region--although it`s
a bit tough to discern since winds are only lazily swinging
around to the northwest in its wake. This front is currently
pressing south of the I-20/30 corridors and will continue to sweep
through the rest of our region through the morning hours. With the
main focus of low-level cold advection slated to remain mainly
near and north of the Red River today, prospects seem good that
temperatures across much of the area will be able to warm up to
above-normal values once again today, even in the post-frontal
airmass. The coolest readings in the mid and upper 50s should
remain confined to our immediate Red River counties, while mid
and upper 60s become more prevalent the farther south you go into
Central Texas. The only thing keeping temperatures from rocketing
back into the 70s across the south will be an increasing veil of
high cloud cover streaming off the subtropical jet which are
registering some light returns on regional radar imagery at this
hour.

Northerly breezes around 15 mph with gusts to 20 mph will
materialize during the mid-morning hours as the pressure gradient
tightens. While dewpoints today will be higher than they were on
Wednesday (in the 20s and 30s) and temperatures will be about
10-15 degrees cooler, this will still result in relative humidity
values heading down below 30 percent across a good chunk of the
region today. Given the parched vegetation and presence of
high fuel loading due to extremely dessicated fine fuels, we`ll
be issuing another Grass Fire Danger Statement today for locales
bounded by a line from Killeen to Greenville to Olney. Once again,
extreme care is urged today if any activities might result in fire
ignition.

Top-down moistening will occur this evening and overnight,
resulting in the development of a rather dense deck of mid-high
cloud cover across the southern half of the CWA ahead of a
sharp/potent mid-level trough axis. Frontogenesis and isentropic
ascent will be occurring within the saturated mid-levels tonight,
but any lift of significance is expected to remain just to the
south of the region. Thus, we`ll keep the forecast dry with silent
10% PoPs over our far southeastern counties. We`ll continue to
keep an eye on this, though, since wet bulb and thermal profiles
would support a rain/sleet mix should precipitation materialize
farther north.

Carlaw

&&

.LONG TERM... /Issued 315 AM CST Thu Dec 14 2017/
/Friday Onward/

The extended forecast will feature our highest rain chances in
nearly 2 weeks (Saturday) followed by continued near/above normal
temperatures.

On Friday morning, a longwave trough axis will be swinging through
the region which will deliver a shot of slightly cooler and drier
air at the surface. As a result, highs should struggle to reach
60 degrees with most locations topping out in the 50s Friday
afternoon. Large-scale subsidence should be occurring on the
western periphery of the trough axis which should lead to clearing
skies as a plume of high cirrus is ushered eastward. At the far
southwestern tail of the trough axis, an upper low is forecast to
become cutoff over Baja California where it will linger for a day
or two before delivering a much-needed opportunity for rain to
North and Central Texas.

Saturday should be off to a cold start with many locations
falling to near or below freezing by daybreak. However, some
changes will begin to take shape by midday as the aforementioned
upper cutoff low ejects eastward towards North Texas. This
shortwave is forecast to be quite potent and will capable of
drawing a plume of warm/moist air northward through the eastern
half of the state throughout the day Saturday. Strong lift from
differential vorticity advection and warm advection should result
in widely scattered showers and perhaps a few thunderstorms,
initially beginning across Central Texas Saturday afternoon and
expanding northward Saturday evening and overnight. There is still
some concern about fire weather conditions on Saturday,
particularly across our northwestern zones where moisture likely
will not recover until after peak heating. Winds will also be
gusty on Saturday 15-20+ mph, so areas that see RHs fall to 20%
or less could see a few hours of near-critical fire danger.

The highest rain chances will occur Saturday evening and Saturday
night as the best moisture and strongest lift arrive. While
light/moderate rain will be predominant, a a few rumbles of
thunder will be possible mostly east of I-35 and south of I-20
where a couple hundred J/kg of elevated instability may exist.
Rainfall totals will generally be higher the farther east one`s
location with some areas west of I-35 possibly missing out
entirely. This shot of rain will be fairly short-lived and most,
if not all of the forecast area should be rain-free around
daybreak Sunday as the vort max quickly exits eastward.

The previous few days, it appeared that a cold front was going to
be pulled through the area on Sunday as a secondary shortwave
swung through from the northwest. This is now appearing less
likely however, and as a result, temperatures should remain on the
warmer side. The good news from a fire perspective is that there
won`t be a boundary to scour out our recovered moisture, so
dewpoints are forecast to largely remain in the 30s and 40s (or
even low 50s) heading into next week. This will help keep RHs
elevated above critical levels.

There are quite a few differences in the large-scale pattern among
guidance through the middle portion of the week so confidence is
relatively low in the Tuesday/Wednesday time frame. It does appear
that another shortwave should eject from its deeper parent trough
over the western US either late Monday or Tuesday which could
result in another chance for rainfall either Tuesday or Wednesday.
The operational GFS is a full 24 hours faster with this
disturbance than the ECMWF and therefore recovers less moisture
and is the drier solution in terms of QPF. The ECMWF on the other
hand, being slower with the shortwave, allows better moisture
recovery and actually suggests another decent shot of rain similar
to what is expected on Saturday. For now, have largely left low
PoPs (10-20%) until there is some better agreement on the large
scale features through this portion of the forecast. Either way, a
gradual warming trend should be underway with temperatures
remaining around 10 degrees above normal.

Some larger changes are possible in the day 8-10 time period when
models have persistently shown deep troughing engulfing much of
the Central US. This pattern would be favorable for delivering
multiple shots of arctic air to the Central US and Southern
Plains, the first of which could arrive in Texas at the end of
next week. By now, we`ve all seen far too many model graphics
irresponsibly floating on social media depicting winter weather
potential due to this pattern shift. While it`s important we
acknowledge some winter weather is a possibility in the Dec 22-27
time frame, it`s much too early to suggest this is a guarantee. It
is something we`ll certainly be monitoring in the next several
days and will introduce if/when appropriate.

-Stalley

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    61  37  57  36  60 /   0   0   0   5  10
Waco                67  37  58  34  57 /   0   5   5   5  30
Paris               57  34  54  32  58 /   0   0   0   5   5
Denton              59  32  56  31  62 /   0   0   0   5  10
McKinney            59  33  55  32  60 /   0   0   0   5  10
Dallas              62  38  57  38  63 /   0   0   0   5  10
Terrell             63  34  57  33  60 /   0   0   0   5  10
Corsicana           65  36  57  35  60 /   0   5   5   5  30
Temple              66  39  59  34  54 /   0  10  10   5  40
Mineral Wells       61  31  55  31  60 /   0   0   0   5  10

&&

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

$$

90/90



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