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

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FXUS64 KFWD 210036 AAA

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
736 PM CDT Wed Sep 20 2017

Quick update to nudge PoPs up into the chance category out across
western zones and expanded the contour of 20 PoP a bit towards
the east closer to the HWY 281 corridor. Also adjusted cloud cover
to match PoP/Wx grids. Otherwise, the remainder of the short term
forecast looks to be in good shape.



00 UTC TAF Cycle

Concerns---MVFR ceiling potential at all TAF sites on Thursday

For the Metroplex TAF sites---VFR is expected over the next 12
hours before southerly winds usher in another round of MVFR
stratus. Current indications are that the moisture surge will be a
bit more potent compared to this morning`s. The MVFR stratus
intrusion won`t be holus-bolus at all Metroplex TAF sites and
southern sites will be first in line for poor flying conditions.
Stratus will overspread the remainder of the Metroplex TAF sites
through the morning hours with VFR returning by noon. Convection
out to the west should have a much harder time making its way
eastwards towards the I-35 corridor, given the weaker deep layer
shear and relatively weaker vigor of convection per latest radar
trends. Nevertheless---will monitor this and amend if necessary.

For the Waco TAF site---An additional round of MVFR stratus is
also expected as a shallow, but rich plume of low level moisture
streams northward. MVFR cigs should arrive around 0900 UTC and are
expected to last through the mid to late morning hours.



.SHORT TERM... /Issued 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.



.LONG TERM... /Issued 330 PM CDT Wed Sep 20 2017/
/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.



Dallas-Ft. Worth    77  95  75  93  74 /  20  10  10   5   0
Waco                76  94  73  93  71 /  10  20  20   5   5
Paris               74  92  71  92  71 /  10  10   5   5   5
Denton              76  95  74  92  72 /  20  10  10   5   0
McKinney            76  94  73  92  72 /  10  10  10   5   0
Dallas              78  95  76  93  75 /  10  10  10   5   0
Terrell             74  94  72  93  71 /  10  10  10   5   0
Corsicana           76  93  72  93  72 /  10  20  20   5   5
Temple              75  93  72  91  70 /  10  20  20  10   5
Mineral Wells       75  95  72  92  70 /  30  20  20   5   0




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