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

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FXUS64 KFWD 200827

Area Forecast Discussion
National Weather Service Fort Worth TX
327 AM CDT Wed Sep 20 2017

Another hot and humid day is in store with high temperatures
expected to climb well into the 90s and even low 100s for some
locations this afternoon. When combined with dewpoints in the 60s
and low 70s, some heat index readings of 105+ are possible. This
is most likely to the west and northwest of the DFW Metroplex
where the low-level thermal ridge should be positioned along a
surface dryline feature, just ahead of a slow-moving front. A Heat
Advisory will not be necessary as these conditions should be a
one-day affair with less oppressive heat expected through the
rest of the week. In addition, a south breeze around 15 mph this
afternoon should provide a bit of relief.

A few showers or an isolated storm will be possible in our
southeast once again this afternoon associated with the seabreeze
intrusion. By late afternoon or evening, the focus will once
again shift to our western counties for the potential development
of a few strong storms. As locations along the dryline begin
exceeding convective temperatures, we should see a few cells try
to develop just west of our forecast area. This missing ingredient
today is any dynamic lift; yesterday`s shortwave that triggered
and sustained convection is now far downstream. If storms are
going to develop, it will have to be due to buoyancy and weak
low-level convergence near the dryline, which typically is not
sufficient for widespread initiation. Will hold PoPs to 20% with
fairly limited coverage expected. Given the strong instability
and weak shear, some strong winds and hail would be possible with
a more robust storm. Expect this activity to largely be confined
to areas west of HWY 281.

Otherwise, low temperatures tonight should be some of the warmest
that we`ve seen so far this month, with most of the area holding
in the mid 70s and urban locations in the upper 70s.



/Thursday through Wednesday/

Thursday: A generally weak flow pattern aloft will encompass the
region on Thursday. An upper level ridge will be positioned over
the Midwest with the axis extending southwest towards Texas.
Persistent southerly flow in the lower to mid levels of the
atmosphere will result in a humid day across the region. Some
afternoon convection may occur in our southeastern counties where
better low level moisture will be as indicated by PWATs near 2
inches, and temperatures are expected to reach forecasted
convective temperatures in the upper 80s. Lift in this area may
also be aided by a weak disturbance wandering around the southern
periphery of the upper level ridge. Forecasts of MUCAPE near 3000
J/kg and wind shear of 10-15 kts support a mode of typical
summer-type convection with a threat for strong winds and/or
downbursts. Elsewhere, without the ridge positioned over the
region, isolated convection may also be possible but will maintain
a dry forecast for now and reassess with the next few runs of
high-res data. High temperatures will be in the 90s and should
remain below the century mark.

There remains split agreement on if another round of convection
will develop Thursday afternoon in southwest flow across West and
Northwest Texas, and if this convection will drift as far east as
our western counties. If there is convective development to our
west, as the low level jet increases in the evening hours, it
could help "steer" it into our western counties and will keep a
low chance for rain mainly west of Highway 281 for now.

Friday through Saturday: The upper level pattern will not change
too much through the weekend with the upper level ridge axis
remaining centered in the Midwest, and a trough over the western
CONUS. Yesterday, the models indicated noticeably drier air
advecting into the region from the east, aiding in keeping a dry
forecast through the weekend. However, the models have since
backed off on that solution and indicate more humid air will
persist through the weekend as deep southerly flow continues.
While some slightly drier air in the mid levels may work its way
across the region, as noted in forecast soundings too, under the
regime of weak flow aloft, we may see very isolated showers and
storms over the weekend. The more likely location for isolated
convection will be across Central Texas where better moisture will
remain. Have maintained silent 10 PoPs at this time but will need
to add higher chances if conditions are looking more promising
for rain. On Sunday, a weak disturbance retrograding around the
southern edge of the upper level ridge along the Middle Gulf Coast
states may advect better quality moisture into our southeastern
and eastern counties, enough for scattered convection.

Monday through Wednesday: The main story for early next week
remains the arrival of a cold front and better rain chances.
While the initial disturbance within the upper level trough to our
west still moves northeast on Monday, there is good agreement in
the latest model runs that the troughing pattern to our west will
persist into the middle of the week and then shift east into the
Plains. The cold front will initially move into Northwest Texas
but will likely stall northwest and north of us as the initial
piece of energy moves into the Northern Plains. However, as the
rest of the trough moves east around the middle of the week, this
should allow the front to slide across the region bringing cooler
temperatures and more widespread rain. Have remained conservative
with rain chances during this period until we can get a better
handle on the timing, but the agreement between the models is
promising. If the front stalls and/or moves slowly, we could be
facing a heavy rain potential, but flooding may not be as a high a
threat due to the dry soil conditions currently occurring across
the region.



.AVIATION... /Issued 1207 AM CDT Wed Sep 20 2017/
06 UTC TAF Cycle

Concerns---Convective cessation at Metroplex TAF sites, wind
shifts and MVFR stratus potential. At Waco...the main concern will
be timing the onset and cessation of IFR and MVFR cigs.

For the Metroplex TAF sites---Convection that developed across
western North TX was able to survive its trek and move
southeastward compliments of sufficient instability and wind
shear. This convection was efficient at producing a large outflow
boundary which has resulted in northerly winds across just about
all of the Metroplex TAF sites. With convection finally decaying,
there shouldn`t be any additional forcing for sustaining the cold
pool and as a result, northerly winds will eventually turn towards
the east and southeast after midnight with a return to south flow
likely for the Wednesday morning push. Coincident with the morning
push, however, will be the appearance of low level moisture and
resultant MVFR stratus. The spatial coverage of MVFR stratus
remains challenging and guidance varies considerably. For now,
will go with simple RH progs which overspreads a large swath of
higher moisture northward. MVFR stratus will likely be
intermittent around FL015-FL018 and so I`ve included temporary
conditions to account for this. Winds should remain elevated and
precludes mention of IFR stratus. VFR will return by mid to late
morning and should continue through the remainder of the TAF
cycle. There may be a low potential for some convection west of
the TAF sites on Wednesday afternoon, but confidence remains too
low for an introduction into the TAFs at this time.

For the Waco TAF site---MVFR stratus will invade before sunrise
on Wednesday with a brief periods of IFR cigs. Low level wind
speeds and subsequent mixing should help cigs to lift through the
morning hours above FL009. MVFR stratus will continue through
around noon with VFR expected thereafter. Convective chances will
remain highest west of Waco, so I`ll maintain a rain-free TAF at
this time.



Dallas-Ft. Worth    98  78  96  76  93 /   5   5  10  10   5
Waco                98  77  94  74  92 /  10  10  20  10  10
Paris               93  74  92  73  92 /   5   5  10   5   5
Denton              96  76  96  74  92 /   5  10  10  10   5
McKinney            94  76  94  74  93 /   5   5  10  10   5
Dallas              97  78  96  76  93 /   5   5  10  10   5
Terrell             94  75  94  73  92 /   5   5  10   5   5
Corsicana           94  76  94  73  92 /  10   5  20   5   5
Temple              96  75  93  73  91 /  10  10  20  10  10
Mineral Wells       99  75  96  73  92 /  10  20  10  10   5




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