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

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FXUS64 KFWD 070906
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
306 AM CST Wed Dec 7 2016

.DISCUSSION...
A somewhat complex forecast in the near term, as we await our
first true arctic blast in almost 2 years and if any light
precipitation will occur once temperatures go below freezing
Thursday morning. Currently, a good chunk of the nation was under
the influence of broad cyclonic flow aloft, with upper low
rotating northward from the Minnesota Arrowhead up into Western
Ottawa Canada. At the surface, the arctic front was oozing
southward through Wyoming and Nebraska.

One more mild day in terms of it being December is expected today
with partly to mostly cloudy conditions under fast westerly flow
aloft on the southern periphery of the aforementioned broad mid
level cyclone. Winds will be generally light with highs mostly in
the 50s.

The arctic front will arrive this evening and have held to the
faster timing of the previous forecast which is close to the TTU
WRF and Euro timing, but faster by 3-6 hours from the NAM/GFS
models. With flow aloft nearly zonal and not much upper support,
initial shallow surges of such cold and dense airmasses are not
tracked well by most of the mainstream synoptic models. The next
challenge comes from sheared absolute vorticity and weak lift
south of I-20 and across Central Texas overnight into Thursday
morning. Intensive analysis of BUFKIT soundings across these areas
show that there will be small window for low chances of drizzle/
rain with patchy freezing drizzle/rain, with the frontal inversion
deepening enough for a brief mixture with sleet come daybreak
Thursday morning. Right now, a majority of the models precipitate
out before the sub-freezing temperatures occur. That said, there
are a few like the SREF Mean that indicate some very light
precipitation may occur afterward.

I did remove any mention of snow despite there being a cirrostratus
canopy expected overhead, as there will be a very dry layer between
700-850mb to overcome and think most ice nuclei would melt or
evaporate before making it into the low level moisture below. It
must be stated that confidence of any winter mix occurring is not
high, as model soundings do dry out low levels toward mid morning
Thursday. Areas that could be affected were generally left the
same, but have removed the patchy drizzle for Thursday afternoon.
With ground temperatures near or just below 50 degrees, any brief
impacts across the southwest counties would be elevated surfaces,
but even then by the time temps fall below 30 degrees, the
precipitation will have long ended.

Some low-mid level cloudiness will linger through much of
Thursday with clearing Thursday night into Friday. The strong
cold advection and brisk conditions will occur Thursday with highs
struggling to make it into the 30s. Frigid temperatures Friday
morning in the teens to lower 20s will be hard-pressed again to
warm a whole lot, despite some modest low level warm advection
later in the day and plentiful sunshine. It`s possibile I may be
too optimistic on Friday`s highs, but I did cut guidance values
several degrees and confidence wasn`t there to go colder right
now.

We will see winds return from the south and become breezy this
weekend, as strong zonal flow aloft allows for strong lee
cyclogenesis to our northwest, while the arctic high transits
eastward across the Mississippi and Tennessee Valleys. Low level
warm advection should help to moderate the airmass across the
area with highs recovering into the 50s Saturday, then even the
lower to middle 60s on Sunday. A shortwave will move east across
the Central Plains Saturday night into Sunday with a cold front
(of non-arctic nature) arriving into the area. Enough moisture
recovery will be present across the eastern counties for some low
convective chances. Though SBCAPE will be nearly absent, there are
signs of mid level lapse rates aloft on the order of 6.5 deg C/KM
to mention at least isolated thunder. We do not expect a lot of
rain from this system, as the previous arctic front will have
scoured the better moisture from the continental shelf right off
the Texas coast.

A generally dry and seasonable week is slated ahead with highs on
55 to 65 with another strong, possible arctic front next Thursday.
The cold front late week does appear to be a dry passage, so no
concerns regarding any winter precipitation in the 7-10 day period.

05/

&&

.AVIATION...
/ISSUED 1128 PM CST Tue Dec 6 2016/
Light north to northeast winds overnight will veer to light
southeasterly during the morning hours Wednesday in advance of an
Arctic front. Moisture return will be meager at best as return
flow will be weak, probably just enough to maintain the lingering
low clouds currently in place. These clouds will likely preclude
fog development in the Waco area (where the higher dewpoints are),
though some minor visibility reductions cannot be ruled out due to
the low dewpoint depressions across Central TX. The DFW area
resides on the edge of a low cloud deck, so things may clear out
periodically during the night. Fortunately the cloud bases are
around 3500 feet so BKN vs SCT shouldn`t make too big of a
difference.

The front will surge south through the Plains overnight, likely
making it into the Metroplex Wednesday afternoon. Hi-res guidance
indicates some light precip with and behind the boundary, but
most of this will have difficulty reaching the ground. Even if it
does, temperatures should remain above freezing for most of the
overnight hours. Slightly better moisture will be in place at
KACT, but feel that it will just not be cold enough at the surface
for any freezing rain or freezing drizzle. That said, we will
still need to keep an eye on trends tomorrow in case future model
runs indicate a colder than expected airmass, or more available
post-frontal moisture.

Either way, strong north winds are expected at all locations
during the overnight hours Wednesday night into the morning hours
Thursday.

30


&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    54  29  37  20  40 /   5  20  10   0   0
Waco                57  31  39  20  42 /   0  30  20   5   0
Paris               49  26  37  19  39 /  10  30  10   0   0
Denton              53  26  37  16  39 /   5  10  10   0   0
McKinney            54  28  37  17  38 /   5  20  10   0   0
Dallas              54  30  37  21  40 /   5  20  10   0   0
Terrell             56  30  37  19  40 /   5  30  10   5   0
Corsicana           57  34  38  20  41 /   5  20  20   5   0
Temple              58  32  39  23  42 /   0  30  20   5   0
Mineral Wells       52  27  37  17  40 /   5  10  10   0   0

&&

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

$$

/05



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