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

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FXUS64 KFWD 062138

Area Forecast Discussion
National Weather Service Fort Worth TX
338 PM CST Wed Dec 6 2017

/Tonight and Tomorrow/

During the day today we received several reports of sleet (mixed
with rain) across Central Texas from Comanche to Anderson County
and south. The rain/sleet mix across our southern counties will
continue to diminish from north to south this evening and tonight,
and all precipitation is expected to end before daybreak
tomorrow. No accumulations or impacts from sleet is expected, and
none have been reported today.

Cloudy skies will remain across most of the region tonight with
the exception being north of Interstate 20. In particular as you
get closer to the Red River, thinning clouds are expected but
should not become completely clear as a steady stream of dense
high cloud continues in advance of the arrival of our next upper
level trough. As the trough approaches from the northwest late
tonight, it will start to push some cooler and drier air into the
region. Most of the cooler air will arrive during the day
tomorrow, but the balance between some cold air advection late
tonight and cloud cover makes for a challenging overnight
temperature forecast. Across Central Texas, dense cloud cover is
expected to keep overnight lows slightly warmer in the mid to
upper 30s. This allows for about a 5-10 degree temperature drop
from current afternoon readings as the rain clears the area.
However, along and north of Interstate 20, overnight lows will
likely be cooler due to thinner cloud cover and the arrival of the
cooler air. For this area, will advertise lows ranging from the
upper 20s to mid 30s with the higher readings in the immediate DFW

Cold air advection will increase during the day on Thursday, and
unfortunately wind speeds will also increase as another
front/surface high brings reinforcing cold air to the region. It
will be a cloudy and breezy day for most of the region, but
again the cloud cover may thin late in the day near the Red River
as the upper level trough arrives. High temperatures tomorrow
will range from the upper 30s in the north to upper 40s in the
south, and high temperatures may have to be decreased for parts of
Central Texas for reasons discussed below.

The main challenge for tomorrow is the small potential for a light
rain/snow mix across parts of the region during the afternoon and
evening hours. The approaching upper level trough is strong and
will spread considerable lift across the region. Isentropic charts
indicate isentropic lift above about 600 mb will increase during
the afternoon hours, in particular south of Interstate 20. With
some possible weak elevated instability, it is possible we could
see isolated to scattered elevated showers develop. Cold air
advection during the day is expected to further dry out the lower
levels of the atmosphere which will work against any precipitation
reaching the ground, but prefer to carry a low chance for a light
rain/snow mix during the afternoon hours south of Interstate 20.
Forecast soundings and wet bulb temperature profiles indicate
snow could be the main winter precip type (mixed with rain) but
some sleet pellets could also occur. The surface and very near
surface layer are both expected to remain above freezing, but IF
any snow makes it down to near the surface, there`s a decent
chance it will melt. IF any snow survives the trip to the surface,
no accumulations are expected due to melting at the surface. If
we do get elevated convective development (or virga due to
evaporation depending on the dryness below the sub cloud layer),
evaporative cooling would be another factor into cooler daytime
temperatures across part of all of Central Texas tomorrow



/Thursday night through next Wednesday/

While generally more quiescent weather is in store for much of
the long term portion of the forecast, we`ll be keeping our eyes
on our far south and eastern counties into Thursday evening as
guidance is now offering some subtle hints at a continued
precipitation potential. Otherwise, a gradual warming trend is
expected into the weekend and early next week as above normal
temperatures return (some upper 60s to near 70 degree highs are
now in the forecast for Monday).

For Thursday evening-night: large scale height falls will
continue to envelope the region ahead of a sharp upper-level
trough axis which will pivot through the region Thursday night and
into Friday morning. Some moisture will remain in place above 700
mb per forecast soundings across the southeastern half of the
forecast area. The concerning aspect to this portion of the
forecast is that lift and elevated instability may still be
present above 700 mb within this region of lingering moisture. An
extremely tight packing of the isotherms ahead of the trough axis
should facilitate the development of a rather robust--yet narrow
and focused--band of frontogenesis between 500 and 700 mb across
our far south and eastern counties. Associated robust isentropic
ascent can be found in model guidance along the 310 K theta
surface within a zone of relatively steep lapse rates. While
coarse-resolution guidance remains quiet on the precip/QPF front,
we oftentimes see precipitation develop in these scenarios where
guidance has misdiagnosed the magnitude of moisture/instability
present aloft. Indeed, the 18z NAM is now showing a sliver of
MUCAPE above 600 mb during this time, which raises some concern
for the development of elevated convective elements. For this
forecast, we`ve added a mention of rain and snow south and east of
an Athens to Killeen line Thursday evening given this latest
guidance. We`ll need to closely monitor trends in model guidance
though, since if convective showers do materialize, wet bulb
temperatures would ultimately support an all snow precipitation
type as surface temperatures fall to near and below freezing.
Obviously, there are a lot of "IFs" in this portion of the
forecast given the subtleties involved, and as a result, we won`t
be showing any snow/sleet accumulations at this time given the
amount of uncertainty.

Otherwise, Friday morning is looking like it`ll be one of the
coldest mornings since this past January as temperatures dip into
the lower and mid 20s across the northern portions of the forecast
area, and into the upper 20s elsewhere. Some guidance is even
hinting that some isolated lows in the upper teens are possible in
the most sheltered and outlying areas, although there may be some
lingering high cloud cover to mute this potential somewhat. Still,
everyone is expected to experience sub-freezing temperatures by
Friday morning, so take care of any tender vegetation which may
have enjoyed the recent November warm spell.

Rather robust upglide will continue, even on the backside of the
departing trough on Friday, but with the best moisture sliding out
of the area, we`ll show a dry and sunnier forecast Friday

Temperatures will moderate nicely over the weekend with highs in
the lower to mid 60s anticipated on Sunday. Another cold front is
forecast to move through the region Monday afternoon and evening
with a reinforcing shot of somewhat cooler air for Tuesday. High
temperatures ahead of the front on Monday near 70 degrees are not
out of the question, especially across the southern half of the
region. Very limited moisture means this front will come through



.AVIATION... /Issued 1151 AM CST Wed Dec 6 2017/
/18Z TAFs/

Concerns... continued wintry mix at/near KACT through the
afternoon hours.

KACT: A mix of rain and occasional light sleet will remain
possible for the next few hours, and then scattered light
precipitation may cross the airport through the remaining late
afternoon hours. No impacts or accumulations are expected from the
light sleet. Otherwise, VFR ceilings will continue to prevail. The
winds will vary between northwest and west through the evening
hours at speeds less than 5 kts. Overnight the winds are expected
to become more northerly, and then speeds will increase late
Thursday morning to around 15 kts with higher gusts.

Metroplex Airports: VFR ceilings will prevail with generally
northwest to north winds at speeds less than 8 kts. Despite light
returns on area radars west of the Metroplex this afternoon, no
precipitation is expected to reach the ground, and a dry forecast
will continue. However, as a strong trough moves into the region
Thursday afternoon, there`s another low chance some sleet pellets
may fall from cloud bases around 120 kft. Wind speeds will
increase to around 15-18 kts Thursday morning with gusts near 25
kts through the afternoon hours.



Dallas-Ft. Worth    36  43  28  55  36 /  10  10  10  10   0
Waco                36  46  26  55  35 /  20  20  10  10   0
Paris               32  42  23  48  31 /  10  10  10  10   0
Denton              29  42  22  53  33 /  10  10  10  10   0
McKinney            31  42  24  51  33 /  10  10  10  10   0
Dallas              37  44  28  53  37 /  10  10  10  10   0
Terrell             32  45  24  52  32 /  10  10  10  10   0
Corsicana           34  46  27  52  33 /  20  20  20   5   0
Temple              36  47  28  55  35 /  50  20  20  10   0
Mineral Wells       31  42  24  55  33 /  10  10  10  10   0




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