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

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FXUS64 KFWD 181850

Area Forecast Discussion
National Weather Service Fort Worth TX
150 PM CDT Sun Mar 18 2018

/Through Tonight/

Main concern through the short term is the potential for isolated
strong/severe thunderstorms this afternoon and evening.

Much uncertainty still surrounds the next ~8 hours of the
forecast, largely due to the stubborn bank of low clouds that have
been slow to scatter through midday. Ingredients are in place for
some thunderstorms to become severe this afternoon, should they be
able to develop. The uncertainties lie largely on the coverage of
storms and the most favorable location for initiation. A pair of
shortwave troughs are currently moving through the Southern
Plains. A deep surface low resides in southeast Colorado while a
more ill-defined low exists across the San Angelo/Abilene area. A
surface dryline is positioned southward through the surface trough
axis, and a stalled frontal zone is draped from east to west
through North Texas. The warm sector bounded by these features has
begun to destabilize with gradual clearing starting to take place
across our western zones where temperatures have climbed into the
low 80s. When combined with dewpoints in the 60s and very steep
lapse rates aloft (as illustrated by the FWD 18z sounding), these
conditions are yielding a narrow tongue of large SBCAPE values
immediately ahead of a westward-bulging dryline.

As lift increases with height falls from the nearby shortwaves
along with low-level convergence near the boundaries, we should
start seeing attempts at convection. Areas that have cleared
immediately along the dryline may destabilize sufficiently to
break the cap or eliminate it entirely, whereas areas to the east
have remained capped due to the presence of widespread low clouds
and substantially cooler surface temperatures. As a result, am
thinking the greatest potential for convective initiation will
probably be along the dryline and near the triple point
intersection with the stalled front. With strong instability and
50-60 kts of deep layer shear, a supercellular storm mode is
likely. If supercells can develop in this area and move eastward
into the warm sector, they will be capable of surviving as
elevated supercells within a capped environment with primarily a
large hail threat. If some clearing/heating occurs through late
afternoon farther east in the warm sector, a wind/tornado threat
would also accompany storms if surface based instability exists.
The weakly capped environment may actually act to enhance the
severe potential if stronger isolated storms can get going. A weak
cap would suppress weaker convective attempts, allowing stronger
isolated supercells to progress eastward unimpeded.

The above scenario is supported by the most recent runs of the
HRRR and a couple other CAMs. However, on the whole, high-
resolution models remain wildly inconsistent with much
disagreement regarding convective initiation locations and
coverage. Some models are developing practically no convection at
all, which I also have to admit is a realistic scenario if enough
lift/instability is not realized. The most likely scenario is
probably a couple of discrete storms developing across
west/northwest portions of the forecast area which will move
eastward with a potential for large hail. Any convection will move
east fairly quickly and exit the area by midnight or so at the

Overnight, the dryline/Pacific front boundary will surge eastward
bringing much drier low-level air through the entire region. This
will scour the low level moisture leading to a cooler Monday
morning with some breezy west winds.



.AVIATION... /Issued 1247 PM CDT Sun Mar 18 2018/
/18z TAFs/

Low clouds have been slow to clear this morning, but are finally
showing some signs of improvement as of 18z. The deck of IFR
clouds is beginning to lift/erode from the west as a shortwave
trough approaches while some warmer/drier air arrives from the
southwest. Will continue IFR conditions through 19-20z before
improving to VFR at all TAF sites through the late afternoon.

The next concern is the potential for convection to impact
airports later this afternoon or early this evening. Coverage of
thunderstorms remains in question, as does the most favorable
location for initial development. Stubborn cloud cover has
prevented strong destabilization from occurring thus far, and this
may inhibit the initiation of more widespread convection
throughout the afternoon. Given the presence of the strong
shortwave to our west, still think isolated thunderstorms are in
the cards especially if lift from the shortwave can be aided by
other boundaries present, such as the stationary front draped
through North Texas or the dryline positioned to the west. Will
continue a brief VCTS mention at DFW Metroplex airports centered
around 00z, but will keep rain-free TAFs at Waco for now.
Southerly winds will prevail through tonight.

Overnight, predominantly VFR conditions are expected as a Pacific
front/dryline moves through the area, although a brief period of
MVFR is possible around midnight just prior to the front`s
arrival. Have not included MVFR in the TAFs for now as the
potential looks low. Drier air behind the front will scour all
low-level moisture from the area and VFR conditions will prevail
into Monday.

A crosswind event is likely to occur through the day on Monday as
breezy west winds of 20G30KT are expected. Later in the day, winds
will turn more to the northwest as a cold front arrives, but will
remain breezy through Monday evening.



.LONG TERM... /Issued 354 AM CDT Sun Mar 18 2018/
/Monday through Saturday/

Strong and gusty west to northwest winds will take hold across
North and Central Texas on Monday in the wake of the most recent
shortwave. While these northwest winds will result in a degree of
cold advection at the surface, the main push of cooler air will
not arrive until Monday evening and overnight with a reinforcing
cold front. As a result, temperatures should still manage to warm
well into the 70s across much of the region under passing high
clouds, with the main exceptions across the immediate Red River
counties where some post-frontal stratus may occur. While some
locations picked up a half inch or more of rain with the activity
on Saturday/Saturday evening, little additional rainfall is
expected today (Sunday). With wind speeds expected to increase to
around 20 mph with gusts to near 30 coincident with dry/cured
fuels and afternoon relative humidity values of less than 25
percent, we`ve hoisted a Fire Weather Watch for locales west of a
Graham to Mineral Wells to Gatesville line late Monday morning and
into the early evening hours. While winds will remain quite strong
to the east of the current watch area, the combination of somewhat
less receptive fine fuels (with ERC-G values running generally
below a critical threshold of 40), and questions regarding
dewpoints and subsequent relative humidity values preclude a
farther eastward extension of the watch area. However, if drier
air materializes, then additional counties may need to be added to
the east of the current watch area in subsequent forecasts.

Breezy conditions will persist into Tuesday as cooler air trickles
south of the Red River, with high temperatures forced back into
the 60s across the region. High pressure will then move overhead
Tuesday night/Wednesday morning, although Pacific moisture
streaming overhead may not allow us to fully reach our radiational
cooling potential.

A warming trend will commence Wednesday and through the end of the
week as southerly surface winds return. Breezy conditions are
expected Thursday and Friday as the next area of low pressure
develops to our north. Based on tonight`s ensemble guidance, the
most recent GFS seems a bit hasty to eject a sub-1000 mb low
pressure system across Kansas Thursday night into Friday, and have
sided with the somewhat slower ECMWF for this forecast package.

There will be a low chance for mainly showers underneath a
strengthening capping inversion over the weekend as North and
Central Texas remain within a region of persistent warm advection.



Dallas-Ft. Worth    57  77  47  65  47 /   5   0   0   0   0
Waco                51  78  47  68  42 /  10   0   0   0   0
Paris               50  73  46  62  42 /  50   0   5   0   0
Denton              52  74  45  65  41 /   5   0   0   0   0
McKinney            50  73  46  63  42 /  10   0   0   0   0
Dallas              57  76  48  66  47 /  10   0   0   0   0
Terrell             53  76  46  65  43 /  20   0   0   0   0
Corsicana           53  76  47  65  45 /  10   0   0   0   0
Temple              51  78  47  69  44 /  10   0   0   0   0
Mineral Wells       49  75  43  66  40 /   0   0   0   0   0


Fire Weather Watch from Monday morning through Monday evening
for TXZ100-115-116-129-130-141>143-156-157.



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