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

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FXUS64 KFWD 180532 AAC

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1132 PM CST Sat Feb 17 2018

/06Z TAFs/

Only minor timing adjustments were made (relative to the 00z TAF
discussion below) on any MVFR/IFR vsbys/cigs through mid-late
morning Sunday, with conditions only improving to MVFR BLO FL020
even in the afternoon, despite increasing warm advection and
increasing SSE winds 10-15 knots by 21z Sunday. The bulk of the
fog looks to occur north of HWY 380 across the north and along and
west of I-35 elsewhere by morning where better low level warm
advection occurs sooner. Have held some -DZ in just west of Waco
and Temple in the higher terrain where some LIFR may be briefly
realized shortly after 12z Sunday.

Otherwise, despite increasing winds and warming temperatures, the
saturated layer will be deep enough to not mix out as much as
previously expected at all airports during the afternoon hours
with possible -DZ and IFR cigs returning at all airports by
Sunday evening. However, with south winds sustaining around 15
knots by then, confidence beyond 21z at this time is not high and
will hold to cigs AOA FL010 for now by 00z/19th.



.UPDATE... /Issued 845 PM CST Sat Feb 17 2018/
Will update for a little more emphasis on patchy-areas of fog
developing across much of the area overnight and lingering through
mid morning Sunday, before improving with increasing south-
southeast winds and warm advection. Some drizzle possible across
western parts of Central Texas as well in the higher terrain.

Currently at the surface, weak high pressure was situated across
much of the area with a weak low pressure trough extending from
the Upper Rio Grande Valley and northeast through the Hill
Country. Light NE winds 5-10 mph is occurring between these
features. However, northeast winds in the boundary layer were
already veering easterly in response to shortwave energy
transversing the fast west-southwest zonal flow overhead in the
mid levels. Short-range models are showing these winds just above
the surface to veer almost southerly by daybreak Sunday 10-20
knots and allow modest warm advection to occur just below an
inversion anchored around 880mb per the 00z FWD sounding from
this evening.

Some advection fog, and even drizzle across parts of Central Texas
are being shown by the HRRR/RAP, NAM, and even the NSSL WRF to
continue developing across Central Texas where better near
surface moisture resides late this evening and just past midnight.
Afterwards, in the cooler air to the northeast, more fog, at
least patchy will form across especially the eastern 2/3 of North
and Central Texas where cooler temperatures are already occurring.
A few areas from Palestine to Cameron are already showing the
early signs of the low level warm advection process initiating
some advection fog and even spotty drizzle as it occurs over the
cool and moist soils from earlier rainfall.

I would be more worried about more widespread dense fog had the
warm advection been stronger just below the inversion and less
mid-high level clouds occurring overhead in the zonal flow aloft.
We certainly couldn`t rule out some localized dense spots overnight
or even a localized advisory for part of the area toward morning,
but for now, it appears dense fog will be mitigated somewhat by
those factors.



.AVIATION... /Issued 637 PM CST Sat Feb 17 2018/
/00Z TAFs/

I will carry VFR conditions with high level cigs AOA FL250 through
much of the evening, though light E/NE surface-925mb flow may
lead to some MVFR VSBYs occurring at all airports just before or
after midnight. Challenges abound with flight restrictions both
w/cigs and VSBYs between 06z-18z Sunday, as 925mb winds veer
southeast and increase, while light ENE winds or calm winds
continue at the surface.

Bands of cirrostratus continue to stream across the region with
shear vort maximums moving quickly through the fast, near zonal
mid level flow aloft. At the surface, weak high pressure was
situated across much of the area with a weak low pressure trough
extending from the Upper Rio Grande Valley and northeast through
the Hill Country. Light NE winds 5-10 mph is occurring between
these features. All rainfall has shunted to the east-southeast of
the area, though some spotty rainfall amounts between 0.25-0.75
occurred near the airports.

A few high resolution models now showing potential for IFR cigs
and spotty BR/FG to develop initially across Central Texas late
this evening, then develop further northward across the DFW Metro
between 08z-12z. I have sped up lower flight restrictions and
dropped them into the IFR category per latest NAM/HRRR projections
by 10z/after at DFW Metro terminals with IFR cigs and MVFR, TEMPO
IFR VSBYS by 12z Sunday. Improving conditions back into MVFR are
expected just before 18z with increasing south-southeast winds
10-15 knots with VCSH possible Sunday afternoon/evening. MVFR cigs
AOA FL020 look to maintain through the afternoon hours Sunday,
before falling back into MVFR BLO FL020 in the 24-30 hour period
for DFW Intl Airport.

For Waco, generally similar trends, just started the diminishing
flight restrictions sooner, or just after 06z Sunday. I held to
similar trends to DFW Sunday afternoon with the only exception
being cigs remaining in the lower MVFR category BLO FL020.

We`ll continue to monitor through the evening and overnight and
couldn`t rule out some spotty LIFR conditions developing in or
near terminals by 12z Sunday if the high clouds can disperse
enough to allow better radiational cooling, though this appears to
be more of an "advection" event versus a "radiational cooling"



.LONG TERM... /Issued 246 PM CST Sat Feb 17 2018/
/Sunday through Saturday/
A spring-like weather pattern is expected to continue through the
week as multiple disturbances move through the southern branch of
the jet stream. The first of these disturbances will move across
the Desert Southwest Sunday while a stronger system moves into
the Pacific Northwest. The approaching systems will strengthen a
surface lee trough across the Central Rockies and bring a steady
return of low level moisture to the region. Patchy fog will linger
through mid morning Sunday, especially south of the I-20 corridor.
A few warm air advection showers will also be possible during the
morning hours with a slight increase in rain chances Sunday
afternoon/Sunday night as large scale lift slowly increases. The
mid levels of the atmosphere will steadily destabilize Sunday
afternoon/night, so an isolated thunderstorm can`t be ruled out.

Rain and thunderstorm chances will continue on Monday as the
western U.S. trough digs into the Desert Southwest and low level
moisture deepens. Although shear and instability will both be on
the rise Monday, the cap will also be strengthening due to
increasing mid level southwesterly flow. The cap should keep any
storms that develop Monday morning elevated but there will be a
potential for some surface based convection Monday afternoon with
an approaching dryline. Therefore, the best chance for strong to
severe storms Monday afternoon/evening will be across the
northwest zones.

Rain and thunderstorm chances will increase Monday night through
Tuesday as the strong upper trough moves across the Rockies and a
cold front moves into North Texas. Lift from both of these
features, coupled with copious amounts of moisture, will bring
numerous showers and thunderstorms along with a potential for
heavy rainfall. There will also be a threat for a few strong to
marginally severe storms. Heavy rainfall will be the primary
weather hazard due to precipitable water values near or above 1.5
inches and a favorable pattern for training storms along and just
behind the front. Of course, the timing of the front will be
critical in determining when and where the heaviest rainfall

Wednesday should remain unsettled across North and Central Texas
as upper troughing in the west lifts moisture over the cold
front. The best rain chances should shift to the east/southeast
through the day Wednesday as the depth of the dry/cold air
increases behind the front. The potential for heavy rainfall and
some flooding will continue, especially across the east and
southeast zones.

A few post-frontal showers will linger Wednesday night across the
southeast zones. The remainder of the region will be dry and much
colder with temperatures falling into the 30s through the night.

Another upper trough will deepen across the Pacific Northwest
Thursday and move southeast through Saturday. This will bring an
increase of low level moisture and lift again, resulting in the
return of showers and thunderstorms to the region.



Dallas-Ft. Worth    46  66  62  75  64 /   0  40  30  40  50
Waco                46  69  63  76  64 /   0  20  30  30  30
Paris               42  60  56  72  61 /   0  30  40  40  50
Denton              43  65  61  75  63 /   0  40  30  50  60
McKinney            43  63  60  72  63 /   0  40  40  40  50
Dallas              47  66  61  74  64 /   0  30  30  40  50
Terrell             45  66  62  74  64 /   0  30  30  30  40
Corsicana           46  69  62  75  64 /   0  20  30  30  30
Temple              46  70  62  73  64 /  10  20  20  30  20
Mineral Wells       44  68  61  78  61 /   0  40  30  30  60




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