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

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FXUS64 KFWD 161010

Area Forecast Discussion
National Weather Service Fort Worth TX
410 AM CST Wed Jan 16 2019

/Today through Thursday Night/

Satellite imagery early this morning shows a shortwave trough
moving east across the Four-Corners region. In the southern
stream, a plume of Pacific moisture can be seen sending a steady
flow of cirrus across South-Central and Southeast Texas. A weak
disturbance within this flow may generate some light precipitation
across the southeastern-most counties today, where slight chance
POPs will remain.

Across the rest of North and Central Texas, a gradual warming
trend will continue in advance of the Four-Corners system and its
attendant cold front. Today`s high temperature forecast will rely
heavily on sky grids, which have been a bit of a challenge as of
late. Slightly veered low level flow will continue to advect
drier air over the western half of the region, where the least
amount of cloudcover is forecast. High temps will subsequently be
in the lower and mid 60s today along and west of I-35. Highs
should stay mainly in the 50s for areas east of the I-35 corridor
where the thicker clouds will be. These forecast values may need
to be adjusted later depending on the exact location of the
clearing line.

For tonight, a strengthening warm air advection regime will
occur as the shortwave enters the Southern Plains, along with a
surface cyclone and trailing cold front. This will result in
patchy fog across the southern third of the region where dewpoint
depressions to reach saturation, along with a chance of light
rain across the far east where the better moisture and modest
forcing for ascent will occur. Low temperatures will range from
the mid 40s across the northwest to the mid 50s southeast.

The cold front will enter the northwestern CWA Thursday morning as
the shortwave races eastward to the Ohio Valley. The front should
cross the I-20 corridor around midday, then slow and possibly
stall around sunset Thursday evening near the southeastern CWA
border as it loses its push. The warmest conditions will (not
surprisingly) be across the southern-most counties where highs
will be around 70. The coolest air will be along the Red River
where upper 50s high temperatures are forecast. The front will
return northward fairly rapidly Thursday night as the next upper
level system develops upstream. One more mild night can be
expected Thursday night with lows ranging from the low 40s along
the Red River to mid 50s across the southern zones.



/Friday Through Tuesday/

A long wave mid-level trough will be sweeping eastward across the
Four Corners/Southern Rockies and toward the High Plains through
the morning hours Friday. Lee-side cyclogenesis to our northwest
will be ongoing in response to the approaching mid-level height
falls and in advance of an arctic cold front sweeping south across
the Northern Rockies and Plains. Gusty south winds 15-20 mph and
strong 25-35 knot south-southwesterly 925-850mb flow will be in
full swing and helping to advect Gulf moisture northward, as
saturation of 850-700mb layer increases through the day. The mid-
level longwave trough will exit over the Central-Southern High
Plains through the day, with increasing pressure advection and
isentropic ascent occurring readily by afternoon with increasing
showers and a few thunderstorms breaking out across the region in
advance of an approaching surface trough across West-
Central/Northwest Texas. Better surface-850mb moisture advection
and low chances for showers and thunderstorms will be possible as
we progress through the morning hours Friday along and east of
I-35/35W. We do not expect any severe weather Friday morning,
though a few stronger storms across this area with SBCAPE less
than 1000 J/KG across southern parts of the CWA, along with mid
level lapse rates greater than 7 Deg C/km, and increasing deep-
layer shear on the order of 40 knots.

Friday afternoon and evening are looking a bit more active
convectively than previous anticipated in advance of our
approaching surface arctic cold front. A slightly further south
and slower motion of the mid level vigorous shortwave approaching
from the west will help to not only induce the expected large-
scale ascent across the region, but will allow 60 dew points to
surge north across those areas along and east I-35 and south of
I-20, setting a 4-6 hour window for strong to a few severe storms
across this region by mid-afternoon Friday and into the evening
hours. Westerly deep-layer bulk shear approaching 50 knots will
coincide with localized SBCAPE values in excess of 1000 J/KG and
the aforementioned relatively steep mid-level lapse during this
time window. Fortunately, veered 0-1km flow around 25 knots will
continue to veer quickly toward the I-35 corridor by 00z
Saturday. Large hail with the aforementioned environment appears
to be the greatest threat, but certainly cannot rule out some
localized damaging winds across particularly those parts of
Central Texas along and east of I-35.

The vigorous main shortwave mid-level trough will swing
progressively east along a slightly more southern track than seen
24 hours ago across the Oklahoma and the Red River Valley Friday
night through Saturday morning. Some threat for a few strong or
severe storms may linger over the southeast counties through
midnight. Meanwhile, a surface low tracking across the Red River
Valley around midnight/after will help to pull the long-awaited
and advertised surface arctic cold front into our west and
northwest counties just after midnight, before exiting Central
Texas by 12z Saturday or shortly thereafter.

Blustery and much colder temperatures will arrive readily by
early Saturday morning. With the slightly further south track of
mid-level shortwave does leave some concern for some wrap-around
moisture occurring across areas especially along and north of I-20
as we progress through the day Saturday. Lingering frontogenetic
forcing in the 925-700mb layer and increasing moisture will occur
across this area, but at different magnitudes and will be fighting
an increasingly strong downglide regime and dry air arriving. Due
to these factors and plenty of model discrepancies regarding
evolution of the environment, I have re-introduced low chances for
a brief transition to a wintry mix across the northeast counties,
with snow flurries from DFW north and west. No travel impacts or
accumulations of any winter weather is advertised at this point,
especially with temperatures during this time frame remaining just
above freezing for areas north of I-20. That said, it definitely
bears stronger investigation through the end of the week. This
will be especially the case if this system continues to track even
further south and slow down.

As a reminder, it`s social media is starting to light up with
worse-case model winter weather scenarios regarding post-arctic
front precipitation along and north of I-20. We ask you to be wary
of such posts and to use only trusted weather sources, such as
your favorite media outlets, National Weather Service, or
established private meteorologists regarding the uncertainty
associated with the forecast on Saturday. Don`t always believe
what you see on social media.

Frigid and blustery conditions will continue in the system`s
wake, as the the arctic front crashes quickly south through the
Texas Gulf Coast Saturday night into Sunday. Rapid top-down drying
of the environment occurs by 00z Sunday driven by strong
isentropic downglide and large-scale subsidence. That said, the
very strong low-level cold advection and shear density of the
arctic airmass surging into the area will maintain gusty north
winds 15-20 mph into Sunday morning. Combined with tanking surface
temperatures into the 20s, wind chill values by Sunday morning
from the single digits north, to the teens elsewhere. If planning
any outdoor activities even for the shortest amount of time, be
ready to wear layers and keep an emergency kit in your car.

Otherwise, due to the depth and density of this arctic airmass, I
leaned toward colder guidance for the post-frontal regime Sunday
into Monday. Highs Sunday will likely struggle to make it out of
the 30s, or lower 40s despite the plentiful sunshine. Insolation
tends to not have the same affects on a dense arctic airmass as it
does other post-frontal airmasses, especially this time of the
year and with such low sun zenith angles. Despite remaining cooler
on Monday, a continued erosion of the arctic airmass should allow
highs to rebound into the mid 40s northeast and mid 50s west.
Increasing warm advection and moisture in advance of our next cold
front the middle of next week will allow lows to stay well above
freezing Tuesday morning with highs rebounding through the 50s to
even some lower 60s across Central Texas. Some low chances for
showers will exist as well Tuesday east of I-35, as moisture
advection ramps up in advance of yet another mid-level system.



.AVIATION... /Issued 1137 PM CST Tue Jan 15 2019/
/06z TAFs/

Nighttime microphysics RGB imagery reveals a sharp back edge to
the expansive deck of MVFR stratus which is currently approaching
the western Metroplex (AFW, FTW) TAF sites as drier air is being
advected eastward on veered 900 mb flow. While this back edge may
clear the western sites shortly, additional warm advection in the
950-850 mb layer is currently materializing to the southwest, and
we`ve seen a recent re-development of splotchy cloud cover as a
result. We`ll move the initial MVFR cigs at FTW and AFW into TEMPO
groups for the next few hours to indicate a (brief) improvement
in conditions, but anticipate that additional low cloud cover will
fill in here overnight. Across the immediate Metroplex sites,
think the threat for widespread fog still remains fairly low with
rather stout flow noted just off the surface, but if skies clear
for an appreciable amount of time before re-developing, then some
4-6SM BR conditions would be possible. Conditions should gradually
improve through the morning/early-afternoon hours and think that
VFR should return by 16/20-21z or so as low-level moisture is
carried just east of the immediate Metro. This reprieve may be
short-lived, however, as the next surge of moisture occurs in
advance of an approaching area of low pressure.

At Waco, cigs are presently VFR, but the next batch of moisture is
swiftly approaching from the southwest. Anticipate a combination
of MVFR cigs and vsbys through much of the overnight with a brief
a period of IFR possible towards daybreak on Wednesday. Based on
the orientation of the low-level flow, it looks like MVFR cloud
cover may hang on through most of the day on Wednesday as moisture
remains trapped under a notable lingering subsidence inversion.
MVFR/IFR cigs and perhaps some BR should build back across the
Waco airfield early Wednesday evening as a 35 kt low-level jet
gets cranking ahead of the next wave of low pressure.



Dallas-Ft. Worth    62  50  63  46  71 /   0   5   0   0  50
Waco                59  50  68  50  72 /   0  10   0   0  30
Paris               55  52  60  43  65 /   0  30   0   0  50
Denton              62  48  61  44  70 /   0   5   0   0  50
McKinney            60  50  60  43  68 /   0  10   0   0  50
Dallas              62  51  63  46  70 /   0   5   0   0  50
Terrell             59  52  63  46  69 /   0  10   0   0  50
Corsicana           58  53  66  48  69 /   0  20   0   0  50
Temple              59  50  69  51  72 /   5  10   0   0  30
Mineral Wells       65  46  63  45  72 /   0   5   0   0  30




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