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

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FXUS64 KFWD 170527 AAC
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1227 AM CDT Thu Aug 17 2017


.AVIATION...
06 UTC TAF Cycle

Concerns---Timing of pre-dawn convection at the Metroplex TAFs.
MVFR stratus potential at the Waco TAF site.

For the Metroplex TAFs---Overall the 00 UTC TAFs seem to be on
track and I`ve not made too many changes. The line of storms
along the slow moving cold front across Oklahoma continues to
exhibit a steady southeast to southerly push, with even some
development ahead of the main line. Short term model guidance
(specifically the HRRR) has come into better agreement with the
remaining consensus of hi-res guidance yielding higher confidence
in the potential for TS. Based on the 00 UTC FWD RAOB and the now
stronger model consensus, have opted to TEMPO TS from 1100 to
1300 UTC at the Metroplex TAF sites. Upstream observations INVOF
storms also indicate MVFR cigs, so I`ve appended this to the TEMPO
TS group as well. Variable winds will also be possible, with
gusts to 25 knots will be possible near thunderstorm outflow and
within thunderstorms.

Thunderstorm activity should decay through mid-morning with VFR
continuing. Southwesterly and/or variable winds will eventually
become southerly through the day. The front instigating this
convection should remain north of the Metroplex TAF sites, likely
mitigating the need for any long term flow changes across D10.
There is a low potential for re-development in the afternoon, but
given the likely widespread cloud cover, think that this potential
is too low to include in the TAFs at this time.

For the Waco TAF site---MVFR stratus appears probable as cigs
around FL025 have already been observed across the TX Coastal
Plain. This should lift northward over the next 2-3 hours and
infiltrate the Waco TAF site. There could be some streamer showers
that develop within the next 6 hours, but at this time, it
appears unlikely. The next concern will be the potential for
convection at the TAF site later in the morning and into the early
afternoon. Reasoning would suggest that convection along the I-20
corridor will produce an outflow boundary which could be a focus
for additional development. At this time, however, it`s unknown as
to how far south activity will get. With this in mind, I`ll hedge
toward a more conservative forecast which maintains a
precipitation-free TAF. If the complex to the north does NOT
subside as rapidly as currently though, an introduction of VCSH or
VCTS may be warranted.

24-Bain

&&


.UPDATE... /Issued 954 PM CDT Wed Aug 16 2017/
The main update to the forecast was to increase PoPs and winds
based on latest analysis and short term model guidance.

Radar and satellite observations this evening indicated a line of
potent thunderstorms stretching from southwest Oklahoma up
towards the Ozarks. These storms were steadily advancing towards
the south ahead of a slow moving cold front beneath broad
southwesterly flow aloft. For tonight, a low level jet is expected
to ramp up with model progs indicating upwards of 35 to perhaps
40 knot flow around 925mb. The resultant isentropic ascent (mainly
along the 310K theta surface), should contribute to the
sustenance of the complex a bit further to the south than
previously thought. In addition, the 00 UTC FWD RAOB sampled an
environment characterized by MUCAPE values of around 4,000 J/kg.
With this in place, parcels that are lifted to around 850mb, will
have the potential to realize some of this instability. With those
factors in mind, have increased PoPs upwards across the northern
half of the area. There is a high bust potential along the
southern edge of the PoP gradient (near the I-20 corridor) as the
magnitude of the nocturnal low level jet will likely be on the
decline as the complex slides southward. At some point, the
feature will decay very rapidly. If the low level jet is slower to
veer and weaken, it`s possible (though appearing unlikely at this
time) that activity could venture down into northern portions of
Central TX.

Outside of additional tweaks to ensure consistency between PoP,
Wx and sky grids, the remainder of the forecast remains largely
unchanged. Updated products have been transmitted.

24-Bain

&&

.SHORT TERM... /Issued 243 PM CDT Wed Aug 16 2017/
/Tonight through Thursday...

An area of modest instability continues across N Texas extending
from Gainesville southward to just west of Waco. This area of
clouds and very isolated and very light showers will continue
moving eastward through this evening.

Some of the high resolution model guidance suggests that isolated
thunderstorms may develop this evening to the west and northwest
of the metroplex and rapidly diminish after sunset.

The cold front moving into Oklahoma tonight should be sufficient
to focus showers and thunderstorms to the north of the Red
River. Some of the models are advertising the possibility of
outflow surging southward into North Texas overnight/before
sunrise with the potential for showers/isolated thunderstorms in
the northern counties. Right now have kept rain chances higher to
the north of DFW but not confident the rain/thunder will be strong
enough to have impacts from DFW southward.

Vanspeybroeck

&&

.LONG TERM... /Issued 715 PM CDT Wed Aug 16 2017/
/Thursday Night, The Weekend, Into Early Next Week/

A stationary surface front will be draped across Southern Oklahoma
with a possible residual outflow boundary somewhere north of I-20
/I-30 left over from Thursday morning`s activity. Isolated to
scattered showers/tstorms will possibly be ongoing along the old
outflow boundary at the start of the period, then wind off after
nightfall Thursday evening. A shortwave disturbance will move out
over the Southern High Plains during this time with new tstorms
generating upstream, then likely congealing into an MCS after
nightfall with the LLJ and associated warm advection establishes
by midnight and after. This complex will likely move into parts of
the Red River Valley, while weakening by daybreak Friday morning
with best chances occurring across the far northeast counties
(that don`t need any more rain) the remainder of Friday morning.
That said, due to the aforementioned veering and weakening LLJ,
we only expect spotty heavier amounts up to an and nothing in
terms of widespread heavy rain, thus no hydrologic highlights are
expected.

The upper high will intensify and build across the area this
weekend making for drier weather, but continued hot and humid
weather fairly typical of August. The old surface boundary nearby
or across our northern counties will likely mix out or be pulled
back northward quickly. That said, surface pressure fields will
be relatively benign with lesser wind speeds and highs continuing
between 95 and 100 degrees. Richer column moisture will exist
from East Texas and the Ark-La-Tex east toward the Lower Mississippi
Valley this weekend, so cannot rule a few isolated, diurnal showers
and storms each afternoon and evening. At this time, the flow
aloft will be weak with the upper high draped across the region,
though high instability could result in a brief stronger storms
with gusty winds and heavy downpours.

As briefly noted above, temperatures to the south of the surface
front/outflow boundary will be hot and steamy with highs 95 to
100 degrees Friday. However, wind speeds of 10 to 15 mph will
likely limit the effects of the heat somewhat. Any areas reaching
near 105 degrees heat index would likely be spotty and we do not
anticipated any heat advisory to be issued, though the usual rules
apply when partaking in any strenuous or recreational activities
outdoors. The heat will remain intact with the expanding and
strengthening upper high this weekend with lighter winds, at which
time heat advisories may need to be considered. We will address
these issues as we get closer to the weekend.

05

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    79  94  78  98  79 /  60  40  20  20  10
Waco                79  97  78 100  77 /  10  20  10  10   5
Paris               73  90  74  93  74 /  70  50  30  40  20
Denton              77  94  76  95  76 /  60  40  30  20  10
McKinney            77  93  76  95  76 /  60  40  30  20  10
Dallas              79  94  79  98  80 /  60  40  20  20  10
Terrell             73  94  76  97  76 /  60  40  20  20  10
Corsicana           78  95  77  97  77 /  20  30  10  10   5
Temple              77  98  76 100  76 /  10  10  10  10   5
Mineral Wells       75  93  74  96  74 /  50  30  20  10   5

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

24/26



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