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

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FXUS64 KFWD 170539 AAC

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1139 PM CST Wed Jan 16 2019

/06z TAFs/

Overall, no major changes were needed to the previous set of TAFs.
Low stratus continues roughly along and east of the I-35/35W
corridor late this evening, but a sharp back edge to the cloud
cover is noted just to the west. Regional VAD wind profilers
indicate that the 975-900 mb flow continues to gradually veer in
response to an approaching area of low pressure which is just
north of the Red River. These veering winds will begin to shove
the pesky low clouds off towards the east shortly. The western
Metroplex sites (FTW and AFW) will be clearing out over the next
hour or so, with Waco and the eastern Metroplex sites following
shortly behind. VFR will then prevail for a period overnight
before post-frontal stratus slides in across the Metroplex after
roughly 17/13z. Based on upstream observations, it seems
reasonable to expect an initial wave of IFR cigs, but bases will
gradually lift as some mixing ensues through the mid-late morning
hours. Just how long MVFR conditions stay in place remains in
question, so opted to portray a blend of the most pessimistic
(NAM) and optimistic (GFS/RAP) guidance. Waco should be far enough
removed from the core of better low-level moisture to maintain
VFR on Thursday morning.

Breezy northwest winds around 10-13 kts will gradually diminish
Thursday afternoon/evening as high pressure builds in from the
west. Surface winds may go light and variable for a time before
light southeasterly flow re-establishes itself later Thursday

In the DFW extended, we`ll need to keep an eye on the potential
for IFR or low-MVFR cigs to re-develop overnight Thursday and into
Friday morning as near-surface moisture won`t entirely be scoured
out. Confidence in this was too low to warrant a cig mention, but
this is something we`ll monitor in future TAF issuances.



.UPDATE... /Issued 829 PM CST Wed Jan 16 2019/
Quick update this evening to introduce drizzle into the forecast
and to expand the mention of patchy fog to locales roughly along
and east of I-35/35E this evening. Surface observations across
parts of Central Texas indicate the presence of fog and drizzle at
this hour, with visibilities generally hanging out in the 1 to 4
mile range. This matches up well with the axis of deepest low-
level moisture, which continues to surge northward ahead of a
developing surface low in the Texas Panhandle. Warm advection in
the 950-850 mb layer will steadily increase through the rest of
the evening hours as a 35-40 kt low-level jet materializes ahead
of this system, supporting the continued development of
drizzle/very spotty light rain showers mainly across the eastern
half of our CWA. Localized visibility reductions to around a mile
or so seem plausible mainly for locales south and east of a
Sulphur Springs to Hillsboro to Killeen line. At this time, it
doesn`t appear that widespread dense fog (visibilities under 1/4
mile) will be an issue, but we`ll keep an eye on observation
trends this evening.

Otherwise, the rest of the forecast is in good shape. Just made
some minor tweaks to the various weather elements to re-trend them
with current observations.



.SHORT TERM... /Issued 252 PM CST Wed Jan 16 2019/

Low level warm air advection will increase tonight ahead of a weak
cold front expected on Thursday. Some partial clearing of low
clouds will continue across the western half of the forecast area
through sunset, but this will only be temporary with low clouds
filling back in during the evening due to an increasing low level
jet. Since wind speeds will remain above 10 mph over most of the
forecast area, the chances for dense fog will be low. The only
exception may be across the southeast zones where wind speeds will
be the lightest, but for now we will keep the visibility above 1

A prefrontal trough will move across the region overnight,
ushering in drier air as it turns the wind to the southwest. This
will result in a steady decrease in low clouds and improving
visibility. The breezy downsloping winds will also keep
temperatures up overnight with lows ranging from the middle 40s in
the northwest to the lower 50s across the southeast zones.



.LONG TERM... /Issued 252 PM CST Wed Jan 16 2019/
/Thursday and beyond/

Cold air has begun to advance southward across the Great Plains.
Morning surface analysis showed a 1033 mb high centered near
Hallock, MN. The air mass associated with this high is quite cold,
with a temperature of -44 C (-47 F) observed this morning at
Stony Rapids, Saskatchewan. In the upper levels, the ridge that
was over the Rocky Mountains yesterday remains there, but is
notably less amplified today. A shortwave trough axis was noted
near the Four Corners with the main longwave trough axis still
just off the California Coast. Meanwhile back on the ranch,
southerly flow is in place across the great state of Texas as a
surface high continues to progress eastwards across the Southeast,
and a weak surface low develops over Oklahoma.

The first issue in the forecast is the potential for lingering fog
in our southern counties Thursday Morning. Patchy fog will likely
be ongoing around daybreak tomorrow morning, but should gradually
dissipate during the morning hours (for more information on the
Wednesday Night/Thursday Morning fog potential, see short term
section). A weak cold front will slide into North Texas during the
morning hours, but this will only really be felt in the form of a
wind shift as winds become northwesterly, but remain light. Skies
may clear out a bit during the afternoon, allowing temperatures
to get close to 60 F for most locations, which will feel mild by
the standards of the last few days.

On Friday, large height falls will begin to overspread the region
ahead of an approaching longwave trough. Strong ascent in the form
of positive differential cyclonic vorticity advection will lead to
increasing rain chances through the day Friday, but the highest
rain chances will come during the evening and overnight hours as
an Arctic cold front comes sweeping down the plain. There may be
enough instability (mostly because of steepening mid-level lapse
rates) to allow for some thunder, thus thunder was included in the
grids for Friday Night. The severe weather potential will be
dependent on how much cloud cover is able to break up during the
day Friday. Right now, it appears that temperatures will stay in
the 60s with cloud cover remaining broken to overcast. Still, this
could be enough to allow CAPE values to approach 1,000 J/kg,
especially in our southern and southwestern counties where warm
air advection may allow temperatures to rise into the low 70s.
There will be a hefty amount of wind shear as well as 100+ knot
upper-level winds associated with the polar front jet overspread
the region. With shear vectors oriented parallel to the surface
cold front, the main storm mode would be linear. This suggests
that the severe threat would be primarily in the form of damaging
wind, though steep mid-level lapse rates could also lead to some
marginally severe hail as well. SPC has hoisted a marginal risk
for severe thunderstorms for most of our forecast area, which
seems very reasonable at this point.

Behind the cold front, strong northwesterly winds will usher
frigid, Arctic air into North and Central Texas. Sustained winds
of 20-30 MPH look pretty likely during much of the day Saturday,
with wind gusts in excess of 35 MPH expected. This would easily
meet our Wind Advisory criteria, thus if this forecast holds, a
Wind Advisory will be required by Friday Afternoon. Strong cold
air advection behind the front will mean that temperatures will
likely fall throughout the day, with many areas seeing their high
temperature during the morning hours. In fact, our hourly
temperature grids indicate 60 F at DFW Airport at the stroke of
midnight Saturday, with the temperature down to 45 F by daybreak,
and down to 37 F by noon. Some precipitation looks to linger
behind the cold front, which always begs the question about winter
weather. The best chance for snow will be along the Red River
where temperatures may drop below freezing before the moisture
moves off to the east. The official forecast calls for a slight
chance to chance (20-40% chance) of a rain/snow mix for areas
along and north of U.S. Highway 380 on Saturday. Given the
marginally freezing temperatures and relatively warm ground
temperatures, little to no accumulation is expected, maybe except
for on rooftops, tree limbs, and other elevated surfaces. The
greatest chances for accumulating snow (and again, these
accumulations would be very light if at all) will be the farther
north and east one goes.

Precipitation should come to an end areawide by sundown Saturday.
Lows look to drop into the 20s across all of our forecast area for
Saturday Night and Sunday Morning, with teens possible in a few
spots along the Red River. Northerly to northwesterly winds of
10-15 MPH will persist through Sunday Morning, leading to wind
chills in the teens across our entire forecast area. Wind gusts
over 20 MPH could even result in "instantaneous" wind chills in
the single digits north of the Dallas/Fort Worth area. Precautions
to protect people, plants, pipes, and pets will need to be
completed no later than Saturday afternoon to prepare for these
very cold temperatures. The official forecast low at DFW for
Saturday Night is 26 F, which is just one degree above the lowest
temperature observed so far this season (25 F back on November
14, 2018), so it`s safe to say that Saturday Night/Sunday Morning
will see some of the coldest temperatures we have seen so far this

Sunday and Sunday Night will be cold once again, with Sunday
afternoon highs only getting into the low 40s, and lows Sunday
Night falling into the upper 20s to lower 30s for most locations.
Much lighter winds should take some of the bite away from the cold
however. That said, if you will be venturing outdoors Sunday
Night to say, watch the Lunar Eclipse, you will certainly want to
bundle up. Clear skies are forecast for Sunday Night, which should
allow for excellent viewing conditions of the eclipse.

Temperatures should moderate as we start off next week. Another
deep upper-level trough (which would bring below normal
temperatures and above normal precipitation chances) looks to
swing into the central CONUS by the middle of next week, but with
significant timing differences between models, the details remain
very unclear right now. The official forecast does however show a
cool down towards the middle of the week, along with increasing
rain chances.



Dallas-Ft. Worth    51  59  46  67  39 /   5   0   0  40  70
Waco                50  64  48  69  41 /  10   0   0  30  60
Paris               50  59  42  63  40 /  10   0   0  40  80
Denton              48  59  44  67  36 /   5   0   0  40  60
McKinney            50  58  44  66  38 /  10   0   0  40  70
Dallas              51  59  46  68  39 /  10   0   0  40  70
Terrell             52  59  45  67  39 /  10   0   0  40  70
Corsicana           52  61  47  69  41 /  20   0   0  40  70
Temple              50  66  50  69  42 /   5   0   0  30  60
Mineral Wells       45  59  45  71  35 /   0   0   0  40  50




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