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

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FXUS64 KFWD 200545 AAC
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1145 PM CST Fri Jan 19 2018

.AVIATION...
/06Z TAFs/

As low level moisture continues to increase tonight, ceilings
will continue to lower into IFR and LIFR categories. LIFR cig
heights are already being reported at KACT where they may remain
for the next few hours. However, an improvement to IFR is
possible around 09Z. Fog and patchy drizzle will continue at KACT
through the night, too. The potential for LIFR cigs at the
Metroplex airports is lower and have kept cigs at an average of
600 feet overnight. New model guidance this evening has trended
towards conditions starting to improve in the Metroplex as early
as 11-12Z, with clearing possibly as early as 14-15Z, and have
moved the timing up a few hours following this agreement between
the newer model runs. Ceilings will likely prevail a few hours
longer at KACT, but all airports are expected to be VFR for nearly
all the afternoon and evening hours. MVFR/IFR cigs will return
Saturday night. South-southeast winds of 10-15 kts through the
night will increase to 12-17 kts with higher gusts during the day
on Saturday.

JLDunn

&&

.UPDATE... /Issued 1010 PM CST Fri Jan 19 2018/

Significant changes were not needed for the overnight forecast,
but new model data arriving recently supports a growing trend that
the clouds may clear a little faster from west to east tonight.
The cloud deck that is already in place across the area will
continue to expand west, but erosion of the cloud deck across the
western half of the CWA appears likely starting after 3 am. By
daybreak, locations along the I-35 corridor could be clearing.

Low level moisture will continue to increase across the region.
Patchy drizzle and fog will continue to occur mainly along and
east of Interstate 35/35W. In addition, some light rain will
likely also occur across our southeastern counties. We will have
to monitor for possible dense fog across our southeastern
counties, but will not issue a Dense Fog Advisory at this time.
Temperatures will show little variation for the remainder of the
night and may increase in some locations.

JLDunn

&&

.SHORT TERM... /Issued 318 PM CST Fri Jan 19 2018/
/Through tonight/

Visible satellite imagery shows extensive cloud cover streaming
northward into the region which roughly bisects the CWA from
southwest to northeast. Temperatures across our southeastern
counties have remained in the lower 50s under the thicker cloud
cover. Areas farther to the west have climbed into the low to mid
60s. For the remainder of tonight, as a strong upper trough moves
into the southwestern U.S., southerly flow will continue to pull
moisture northward. Low clouds are expected to thicken and spread
a little farther west than they are currently located. In
addition, the depth of the moisture will increase overnight
possibly resulting in some patchy drizzle or light rain. We`ll
keep some 20% PoPs across most of our eastern counties during the
overnight hours to account for this. Otherwise, temperatures will
only drop into the 40s tonight with the increase in cloud cover
and low level warm advection.

Dunn

&&

.LONG TERM... /Issued 318 PM CST Fri Jan 19 2018/
/This Weekend Through Thursday/

Low level warm advection and shallow moisture advection below an
inversion anchored below 850mb will be ongoing Saturday morning.
A few areas of drizzle will be possible across the eastern
counties through mid morning, before rapid warming and mixing
allow for occasionally gusty south winds and low chances for a few
light showers across this same general area with highs in the 60s.
Further west, partial sunshine will allow temperatures to warm
between 70 and 75 degrees. By Saturday night, gusty southerly
winds, mild temperatures, and a few showers across the east will
continue as a strong shortwave trough swings east across the
Great Basin and over the Four Corners or Southern Rockies by
Sunday morning. Winds may briefly go light enough early in the
morning for some fog as well, but winds speeds should remain high
enough for any fog not to be dense.

Increasing warm advection through 700mb late Saturday night into
Sunday morning will help to induce a few showers across all but
areas west of U.S. 281 in response to a lead piece of shortwave
energy lifting east across the Southern High Plains. Modified
surface dew points only in the 50s and a stout, elevated inversion
in the 850mb-700mb layer will preclude any potential for thunder
as surface based instability remains marginal. The surface dryline
will respond to deep mixing and strengthening mid level height
falls across the region quickly and be likely moving to, or even
past the I-35 corridor in the north as deep ascent approaches the
area. Very strong boundary layer winds of 40-45 knots in
combination of a very tight surface pressure gradient will likely
result in surface winds of 15-25 knots with gusts to 35 knots,
with a potential for a future wind advisory on Sunday for parts of
the area. We will continue to assess the winds on Sunday.

Otherwise, clouds will clear rapidly behind the dryline, while
clouds across the east only partially break out for highs mostly
in the lower 70s across the area, with upper 50s and lower 60s
surface dew points surging into our eastern Central Texas
counties. As prime daytime heating coincides with the ascent from
both the dryline and vigorous shortwave, scattered showers and
storms will develop across the southeast half of the CWA. However,
SBCAPE values will likely not exceed 500 J/KG across this area,
with elevated lapse rates between 6.5-7 deg/C. With unidirectional
southwesterly strong wind shear in place, I cannot argue the
marginal risk from the SPC in place across this area, though do
agree that instability will be very "conditional" with the best
forcing aloft occurring north and northeast of the area.

A few strong to marginally severe storms could develop by early
Sunday evening with very gusty winds and frequent lightning the
main concern. Again, any brief severe weather threat would be very
conditional on moisture quality and depth from the boundary layer
to the surface to sustain enough instability to sustain updraft
strength and not have the strong shear in place topple them over
beforehand. Meanwhile west of the surface dryline, low afternoon
humidity values below 30 percent and gusty west- southwest winds
will combine with dry fuels from previous fuel loading last Summer
and a lack of appreciable precipitation to result in a critical
threat for grass fires. We have continued the Fire Weather Watch
for much of western North Texas Sunday into Sunday evening. If all
the above trends continue through this time tomorrow, it is
likely that all, or parts of the area would be upgraded to a Red
Flag Warning. Otherwise, many other areas would likely be in a
Grass Fire Danger Statement.

The vigorous shortwave trough will occlude into an upper low and
move readily northeast across the Central Plains and toward the
Mid and Upper Mississippi Valley and Midwest Sunday night and
Monday morning. A surface cold front will arrive Sunday evening and
overtake the dryline and shunt all storm chances east of the area,
with brisk and much cooler weather arriving to begin the work
week. Mid level flow will dampen to a more zonal regime through
mid week, before shortwave ridging sets up in advance of another
system arriving the last weekend of January. Dry weather persists
during this period with mostly clear skies until late week when
warm advection brings stratus back northward by Friday. Mornings
will start off seasonably cool in the 30s, but warm into the upper
50s to mid 60s each afternoon, as a secondary cold front arrives
and reinforces the dry airmass in place Tuesday night. As for next
weekend`s system, too many details need to be worked out by the
models and it`s currently beyond the 7-day period.

05/

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    51  68  57  73  42 /  10   5  20  40   5
Waco                50  68  56  72  41 /  10  10  20  50  10
Paris               46  63  54  67  41 /  20  20  20  60  40
Denton              49  67  53  71  39 /  10   5  10  30   0
McKinney            50  66  54  70  40 /  10  10  20  50  10
Dallas              51  67  56  72  43 /  10  10  20  40   5
Terrell             51  66  57  70  41 /  20  20  20  60  30
Corsicana           49  65  56  71  42 /  20  20  20  60  40
Temple              47  68  55  72  41 /  10  10  20  50  10
Mineral Wells       46  71  51  71  37 /   5   5   5  20   0

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Sunday morning through Sunday evening
for TXZ091-092-100>102-115>117-129>132-141>143.

&&

$$

82/30


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