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

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FXUS64 KFWD 202030

Area Forecast Discussion
National Weather Service Fort Worth TX
330 PM CDT Wed Sep 20 2017


We continue to see a cold front overtaking the surface trough/
dryline from south of Vernon, to Snyder, to near Lubbock this
afternoon. The cold front has shown signs of slowing the past few
hours due to the intense heating with temperatures into the mid-
upper 90s out ahead of this feature. The only difference from this
time yesterday is the subtle shortwave disturbance is much further
east with subsidence over the potential convective initiation
area late this afternoon and evening. Even so, surface convergence
should be able to initiate widely scattered tstorms along this
boundary just W-NW of our western counties by early evening. The
subsidence should result in less convective coverage, but with the
strong lapse rates both below cloud base and aloft, along with
highs out that way near the century mark, cold pool propagation of
any storms that do develop is likely.

Now, depending on what model you choose, we`ll either see a few
strong to severe storms develop just NW of our CWA (TTU & NSSL
WRF), then cold pool into our W/NW counties well west of I-35/35W,
or see not much development at all with any storms quickly
dissipating by nightfall (HRRRx and 3km NAMNEST). Knowing the
superiority of the WRF models in this type of `conditional`
development situation and their ability to cold pool activity ESE
past nightfall, have learned toward these models for tonight`s
convective forecast. Though coverage should be less, there are
enough signs from the TTU and NSSL WRF models to push slight
chances to just west of the I-35W corridor and north of I-20. I
did not bring the slight chances quite that far east, but this is
something our evening crew will have to monitor with any convective
development and cold pool propagation. A few strong, to even
brief severe storms are possible considering the thermodynamic
environment noted beforehand.

Otherwise, I have lingered slight chances across the far SW
counties for the overnight in anticipation an old outflow boundary
could linger across that area. Otherwise, we anticipate
occasionally gusty south winds near 15 mph overnight and another
surge of stratus overnight, especially for areas along and E of
I-35. The combination of both, along with high dew points will
result in yet another Summer-like, breezy, and humid night. Now
temperatures could get cooled off more if storms do develop and
affect parts of the western CWA, but right now this is too
conditional at this point to adjust low temperatures currently in
the 70s down across those western counties.



/Thursday through Wednesday/

With the primary 500 mb ridge axis positioned well off to our
north and east on Thursday, the mid-level flow will remain fairly
weak and chaotic. There is a small potential that (much like this
morning), that some weak elevated convection may be ongoing
Thursday morning across our far northwestern zones within a mid-
level moist-axis centered around 600 mb or so. That said, any
subtle forcing of significance looks to remain just north of the
Red River, and will maintain a dry forecast here through the
morning hours. As temperatures warm into the 90s during the late-
morning/early-afternoon hours, isolated to scattered showers and
thunderstorms are expected to develop within an axis of greatest
moisture across the southeastern third of the CWA. There are also
some hints that an additional subtle wave aloft (most evident in
this morning`s run of the ECMWF) may impinge upon our northwestern
counties, and feel that this warrants an introduction of low
(20%) PoPs during the afternoon given the warm temperatures and
sufficient moisture. Soundings here look somewhat subsident just
under 500 mb, and this should help limit any coverage to just
isolated across this portion of the forecast area. Weak flow on
Thursday should preclude a severe threat, but some strong wind
gusts will be possible with any of the more robust convection
during the afternoon.

Very little change to the pertinent large-scale weather features
is forecast across the region by Friday and Saturday, although
mid-level heights should rise a bit in response to deepening
troughing across the Great Basin. The lack of notable forcing
mechanisms, in concert with slightly drier air overall, support
the continuation of a dry forecast through the upcoming weekend
for the time being. A rogue shower or two cannot be ruled out,
but this potential is simply too low to warrant an explicit
mention in the worded forecast at this point.

Big changes are on the horizon next week, however, as the
aformentioned troughing to our west finally begins to migrate
north and eastward, which should help send a cold front towards
the Red River sometime during the Tuesday-Wednesday timeframe.
Recent runs of the GFS and CMC remain the most aggressive with
this front and attendant precipitation chances, delivering fairly
widespread showers/storms to the area by Monday night/Tuesday
morning. The associated ensemble guidance (GEFS/GEPS) on the other
hand, support a slightly slower solution, more in line with the
recent ECMWF. Given the degree of troughing present to our west
and the potential for shortwave energy to take a bit more time
digging into the base of the trough axis, this forecast will side
a bit more with the slower ECMWF, with the greatest precipitation
chances occurring on Tuesday and Wednesday. Given improving model
support, we have bumped PoPs up as well during this time frame.
The best kinematics look to lag the front for the most part, which
should limit the severe weather potential. Copious moisture,
however, spells a potential for moderate to heavy rainfall with
this incoming front as several waves of upper-level ascent will
zip across the region during this time frame.



.AVIATION... /Issued 100 PM CDT Wed Sep 20 2017/
/18Z TAFs/

Challenges through Thursday morning will be if any isolated
strong-severe storms out west will be able to cold-pool toward
I-35 again late this evening, along with timing/coverage of MVFR
cigs by sunrise Thursday morning.

Look for VFR conditions to persist until the pre-dawn hours
Thursday, when a LLJ helps surge MVFR stratus northward across
particularly those areas along and E of I-35/35E. I will carry
prevailing MVFR at Waco by 08Z, then Love Field and Arlington by
11Z. I will persist the MVFR cigs until mid morning, or when mixing
and heating result in a scattering of the stratus deck with VFR
conditions on Thursday. Otherwise, continued S winds 12-16 kts
will prevail, with occasionally higher gusts with the boundary
layer remaining partially coupled.

A weak shortwave trough aloft trough continues to move east across
E TX into NW LA/SW AR. Meanwhile a slow moving cold front was
moving into NW TX/SW OK, with a surface trough tailing SSW from
just west of Wichita Falls to near Snyder. Isolated, high-based
light shower activity noted on satellite and radar earlier north
of I-20 has weakened, as it moves away from the low level theta-E
ridge out of ahead of the cold front and weak surface trough
across NW TX. However, spotty new CU development is being noted
along the surface trough from Ozona/San Angelo to near Brownwood.
We will look for a few strong to severe storms to develop between
21z-00z once again, but not as much coverage as Tuesday, due to
some mid level subsidence from the departing shortwave.

A few models show a similar cold pool surge toward I-35/35W by
late evening once again, while others hardly develop any convection
or cold pool scenarios across the west bound and Bowie corner
post routes. For now, will leave any potential VCTS out of western
DFW Metro airports (AFW/FTW), but this will need to be monitored
closely early this evening once again.



Dallas-Ft. Worth    77  95  75  93  74 /  10  10  10   5   0
Waco                76  94  73  93  71 /  10  20  20   5   5
Paris               74  92  71  92  71 /   5  10   5   5   5
Denton              76  95  74  92  72 /  10  10  10   5   0
McKinney            76  94  73  92  72 /   5  10  10   5   0
Dallas              78  95  76  93  75 /  10  10  10   5   0
Terrell             74  94  72  93  71 /   5  10  10   5   0
Corsicana           76  93  72  93  72 /   5  20  20   5   5
Temple              75  93  72  91  70 /  10  20  20  10   5
Mineral Wells       75  95  72  92  70 /  20  20  20   5   0




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