Forecast Discussion for Dallas/Ft. Worth, Texas

FXUS64 KFWD 181745 AAB

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1245 PM CDT Sat Aug 18 2018

/18z TAFs/

Surface winds continue to slowly veer in response to an
approaching surface trough and may eventually (briefly) become
more northerly late this afternoon. Winds remain quite light
behind the incoming boundary, so area airports may be able to
remain in a south flow. As the airmass destabilizes, thunderstorms
should begin to develop within an axis of higher moisture and
enhanced surface convergence just to the west of the D10 TRACON.
Exhausted outflow could set off additional thunderstorm
development closer to the Metroplex TAF sites, but anticipated
coverage still remains a bit too low to warrant introducing a
TEMPO group at this point. We`ll monitor satellite and radar
trends this afternoon since this addition may become necessary in
future TAF issuances. A microburst threat will accompany any
stronger cells this afternoon.

This activity will dwindle with the loss of heating this evening,
but additional robust lift will overspread parts of North Texas
around midnight. The strongest lift and best moisture is forecast
to reside just north of the Metroplex TAF sites, so we`ll continue
to simply advertise VCSH through daybreak on Sunday, although I
can`t completely discount the potential for some embedded
lightning strikes. A thunderstorm complex may be trekking towards
the Bowie Cornerpost, but veering low-level flow and the main
instability axis shifting north of I-20 should keep this activity
from directly impacting the TAF locations. If a coherent outflow
is exhausted from this activity, a brief northwest wind shift
could occur between 11-15z or so.

After a lull in activity Sunday morning, additional showers and
storms should develop during the afternoon as a stronger shortwave
dips into southern Oklahoma. We`ll advertise VCTS after 19/22z in
the DFW extended.



.UPDATE... /Issued 1124 AM CDT Sat Aug 18 2018/
The inherited forecast remains on track. Adjusted the near term
grids to reflect ongoing observational trends, and nudged high
temperatures up a degree or two area-wide with most locales
already running 3 to even 5 degrees warmer than this time
yesterday morning. Winds are responding to the approach of a
surface low pressure trough, and will continue to veer to favor a
west to west-southwesterly direction this afternoon. The
combination of this additional downsloping component and 850 mb
temps of +22 to +24 C support high temperatures creeping into the
101-104 degree range across the Metroplex, and above the century
mark for most of our forecast area. Moisture is pooled immediately
ahead of and just behind a weak "cold front" north of the Red
River, with dewpoints jumping into the mid 70s across parts of
southern Oklahoma.

Think most of our area will still be able to mix dewpoints out a
bit this afternoon, save for our far northern tier of counties
where dewpoints may remain steady or even slowly rise as this
boundary approaches. Heat indices are now forecast to top out in
the 105-108 degree range mainly from I-35 and points east, and
north of I-45 today, well into Heat Advisory criteria. However,
the expectation is that these high heat index values will shift
southward tomorrow, limiting the duration of the oppressive heat.
With this in mind, we`ll abstain from issuing a Heat Advisory
today since we won`t quite be making our 2-day criteria.

The PoP forecast is in good shape, and expect isolated to
scattered storms to develop later this afternoon with the highest
coverage west of I-35 and north of I-20. A typical summertime
strong-severe downburst wind threat will accompany the strongest
cores into the early-evening hours.



.SHORT TERM... /Issued 430 AM CDT Sat Aug 18 2018/
/Through Tonight/

A surface trough axis is draped through North Texas this morning,
positioned roughly from Abilene to Paris. Aside from the wind
shift across it, this feature is barely recognizable although it
will have substantial implications on today`s forecast. Low-level
warm advection is occurring in the trough`s vicinity, which will
remain maximized over Northeast Texas through this morning. The
associated ascent will allow for isolated rain showers to continue
east of I-35 and north of I-20 through daybreak.

This afternoon, the boundary layer will destabilize while
becoming uncapped, and low-level convergence along the surface
trough should result in scattered convective development. The
favored area for initiation should be roughly west of I-35 and
north of I-20 where low-level convergence will be strongest.
Storms in this area will pose a downburst wind threat due to
deeply-mixed inverted-V soundings and surface T/Td spreads
exceeding 35F. Otherwise, temperatures across most of the forecast
area should be a degree or two warmer than yesterday, primarily
due to the veering of winds to a more westerly direction near and
south of the trough axis. Have sided with the warmest temperature
guidance today due to this increased westerly wind component.

While our diurnally-driven thunderstorms will begin to fade this
evening, dynamically-driven convection will continue across the
Texas Panhandle region overnight as strong height falls occur
ahead of a deepening upper trough. Persistent ascent should allow
a disorganized area of showers and embedded thunderstorms to move
through portions of southern Oklahoma and possibly through some
of our North Texas counties overnight and into Sunday morning. The
strongest forcing during this time period is progged to remain to
our north, thus we may only catch the trailing southern end of
activity while the bulk moves through Oklahoma. Will maintain PoPs
of 20-40% overnight, maximized across our Red River counties.



.LONG TERM... /Issued 430 AM CDT Sat Aug 18 2018/
Showers and thunderstorms will likely be ongoing across Oklahoma
at daybreak Sunday. Some of these cells may slip south of the Red
River during the daylight hours Sunday morning, but the bulk of
the activity will be inclined to eject into the Ozarks with a
departing impulse aloft. Morning showers and storms may also
accompany the associated cold front, which at that time could be
as close as Northwest Texas and the Big Country. These cells would
also tend to move northeastward, reducing the chances that they
impact much of North Texas during the morning hours.

As the main shortwave departs, the front may struggle to make much
progress during the day Sunday. It could still be the focus for
renewed development during the afternoon, but any lingering
outflow may be effectively erased by strengthening southerly flow
in the boundary layer. Aside from some convective debris north of
the I-20 corridor, abundant sunshine will push temperatures into
the upper 90s to near 100 degrees. With dew points still near 70F
at peak heating, heat index values should top 105, particularly in
areas south of I-20 and east of I-35. Without any surface focus,
this extraordinary instability will likely not be realized, but
there may be a narrow corridor near the I-20 corridor that is both
far enough north to have reduced inhibition yet far enough south
to have sufficient potential instability. If any cells are able to
develop, they could become severe with damaging winds the primary

The greater potential for showers and storms will be overnight
Sunday night into Monday morning as the front begins peeling up
the unstable air across North Texas. While there will be adequate
nocturnal instability on which to feast, these convective elements
will be well separated from the better forcing to our north. As
the main upper trough heads toward the Mississippi Valley, our
front will again lose its forward momentum and may hang up across
Central and East Texas Monday afternoon. This may push prefrontal
temperatures near or in excess of 100 degrees while enhancing the
potential for strong thunderstorms along the stalled boundary.
Northerly flow aloft will then increase, and the front should
surge through the remainder of Central and East Texas Monday night
with attendant showers and storms. With some uncertainty in
timing, some low-end PoPs will linger in our far southeast
Tuesday morning.

While the postfrontal air will not be particularly cool or dry --
it is still August after all -- it will be noticeably more
pleasant than this weekend`s oppressive heat and humidity. Daytime
temperatures should stay near or below normal into Thursday, at
which point southerly winds will finally return. There is still
considerable disparity among extended guidance regarding the
forecast for the end of next week. The GFS series maintains
northerly flow and rain chances while the ECMWF and CMC favor
late-season ridging. Will carry some slight chance PoPs in some
areas, but will keep the bulk of the forecast area dry.



Dallas-Ft. Worth   102  79  97  77  93 /  20  20  20  40  30
Waco               103  78 101  77  98 /  10  10   5  20  20
Paris               97  76  93  75  91 /  20  20  30  50  40
Denton             100  78  96  75  93 /  30  30  20  40  20
McKinney            99  77  96  76  93 /  20  20  20  40  30
Dallas             102  81  97  77  94 /  20  20  20  30  30
Terrell            100  78  97  77  93 /  20  20  10  30  30
Corsicana          101  78 100  77  97 /  10  10   5  20  30
Temple             101  76 101  77  99 /   5  10   5  10  20
Mineral Wells       99  76  98  75  92 /  40  30  20  40  20





NWS FWD Office Area Forecast Discussion