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

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FXUS64 KFWD 290852

Area Forecast Discussion
National Weather Service Fort Worth TX
352 AM CDT Thu Jun 29 2017

/Today through Friday/
The usual bands of nocturnal stratus associated with the
advection of rich Gulf moisture will mix out by mid to late
morning and reveal mostly sunny skies areawide by midday.
Temperatures will be a couple of degrees warmer than yesterday as
winds become more southerly at the surface and southwesterly at
850mb. Humidity will remain high and heat indices today will top
out in the upper 90s to near 100 for most of the area. A weak
upper level trough axis will remain draped across Louisiana and
the Texas coast and will provide the lift for scattered showers
and storms along southeast of the feature. There remains a very
slight chance that an isolated shower could affect the far
southeastern zones today, but have elected not to mention this in
the worded forecast as this activity will remain southeast of the

Southerly winds will increase tonight and especially on Friday as
a surface low moves into the Texas Panhandle and tightens the
pressure gradient over the region. Lows tonight will be above
normal with readings only bottoming out in the mid to upper 70s.
Highs on Friday will again be warmer and should reach 100 in the
western zones, but the breezy southerly winds at 15 to 25 mph will
keep the central zones in the mid 90s with lower 90s over the
eastern areas. These temperatures combined with high humidity will
push heat indices above 105 in much of the central and western
parts of the CWA. However, given the high wind speeds the heat
will not be as bad as what we saw last Friday. A strong cap will
remain in place through the day Friday, so any threat of
convection will hold off until after sunset.



/Saturday through Tuesday/

The fun truly begins after Saturday midnight and through the pre-
dawn hours on Saturday. Model guidance has changed somewhat
substantially over the past 24 hours with respect to the position
of the summertime cold front. The NAM, Canadian and ECMWF all
generally agree that the front will near or slip just south of the
Red River sometime late Friday night into the pre-dawn hours on
Saturday morning (which is much less progressive than 24 hours
ago). The GFS on the other hand, keeps the surface front a bit
farther north closer to the I-40 corridor in Oklahoma. With a
slower progression evidenced in all model guidance, convection
before 00 UTC Saturday appears most unlikely given little to no
synoptic forcing and the strong capping inversion that will likely
be in place as 850mb winds veer. The question then becomes which
solutions seem more plausible with regards to the southern extent
of the convection. Given that the front should likely slide a bit
farther south than advertised by the 00 UTC GFS, I`ll lean more
with the Canadian/NAM/ECMWF model consensus which still is a bit
farther north than previously thought/forecast. Preliminarily
looks at the NAM NEST and TTU WRF still indicate a good chance for
showers and thunderstorms near and north of the Highway 380
corridor, so I`ll keep chance to likely PoPs here during the
overnight hours into Saturday morning. Farther south--- the
forecast becomes a bit more difficult and uncertain. GFS and NAM
forecast soundings indicate a stout cap will be in place which
should no doubt suppress any free convection ahead of the main
complex. As the complex shifts eastward, it should ingest rich low
level theta-e air compliments of a strong 925mb low level jet.
The main caveat will be does any trailing convection have the
ability to overcome the surface based inhibition and utilize the
available instability above the capping inversion. Given this
uncertainty, I will taper PoPs off rapidly towards the south as
there is still the potential for some regeneration of convective
cells along the southern edge of the complex.

With regards to the severe weather potential---models have backed
off on the magnitude of the mid level flow (thus perhaps why they
aren`t all as aggressive with the southward progression of the
front). The weaker mid-level flow yields lower deep layer wind
shear values, only on the order of 20 or so knots as opposed to
the 30-35 knots previously advertised. Instability values,
however, remain quite robust with model progs indicating that the
near-storm environment will be characterized by CAPE values of up
to 2,500 J/kg. With a large amount of dry mid-level air present,
the potential for expansive cold pool generation is still quite
appreciable and we will continue to advertise a threat for strong
damaging winds---if storms develop. If a strong cold pool does
develop, it will mean that areas south of the Highway 380 corridor
would see a greater potential for rain during the overnight hours
on Saturday. Heavy rain may also result in some instance of
flooding, especially along the Red River Valley.

By sunrise Saturday morning, the complex of storms should still
be ongoing with highest rain chances across northeastern and
eastern sections of North TX. I will continue to advertise low
rain chances as far south as the Temple/Killeen Metro areas given
the uncertainty on the southern edge of what should be a slowly
decaying complex. Any remnant outflow boundaries could serve as a
catalyst for additional development through the day on Saturday across
Central TX. Given that most of this convection would more than
likely be driven by mesoscale boundaries, I`ll elect to only retain
the 20 PoP inherited for Saturday afternoon and evening across
Central TX.

With the slightly zonal flow aloft, some models actually suggest
a re-invigoration of deep moist convection back across the Big
Country into western North TX late Saturday and into Sunday
morning. The vigor of the pre-dawn storms on Saturday will
ultimately dictate whether or not this potentially second round of
robust convection develops late Saturday into Sunday. For now,
I`ll advertise just low rain chances along the Red River through
the overnight hours. If a robust complex of storms can develop,
there will be a potential for strong winds and heavy rain. As
noted in previous AFD`s, if a couple of rounds of storms do
materialize there may be a concern for flash flooding.

For Monday and Independence Day---a rain-free forecast for North
and Central TX appears appropriate given that the conveyor of
stronger westerlies will be displaced to the north. Furthermore, winds
at the mid an upper levels are only on the order of 15 to 25
knots, pretty typical for this time of year. With no real signal
for large scale lift, I`ll go with a dry forecast. Given the
moist airmass likely in place, however, we will have to keep an
eye on the potential for any diurnally-drive convection, but for
now, this signal seems faint as well. Otherwise, conditions will
be quite seasonal with temperatures in the mid 90s and heat index
values nearing the 100 to 105 degree range.



.AVIATION... /Issued 1125 PM CDT Wed Jun 28 2017/
Low level flow has decoupled and surface winds have fallen below
10 KT at all locations. Wind speeds may increase slightly over the
next few hours as a 25-30 KT low level jet develops, but the main
concern should be an influx of stratus during the overnight
hours. Ceilings are expected to fall to MVFR in the Waco area
around 09Z, then around 11Z in the Dallas-Fort Worth Metroplex.
Conditions will improve during the mid to late morning hours and
VFR is expected at all TAF sites by midday Thursday. Otherwise,
any foreseeable convective weather during this forecast cycle
will remain either well south along the coastal areas or well
north in the Central Plains.



Dallas-Ft. Worth    93  78  96  75  91 /   0   0   0  30  40
Waco                94  77  96  77  96 /   0   0   0   5  20
Paris               90  74  92  74  86 /   0   0  10  40  60
Denton              93  77  96  75  91 /   0   0   5  40  40
McKinney            91  77  94  75  90 /   0   0   5  40  50
Dallas              94  78  96  75  92 /   0   0   0  30  40
Terrell             91  77  94  74  92 /   0   0   5  20  40
Corsicana           92  75  94  76  93 /   5   5   5   5  30
Temple              94  76  97  76  96 /   0   0   5   5  20
Mineral Wells       94  75  98  74  94 /   0   0   5  40  30




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