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

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FXUS64 KFWD 170254 AAB

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
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.



.AVIATION... /Issued 715 PM CDT Wed Aug 16 2017/
00 UTC TAF Cycle

Concerns---Convective potential at the Metroplex TAF sites and
MVFR ceiling potential at the Waco TAF site.

For the Metroplex TAF sites---VFR is expected to prevail through
a majority of the TAF cycle. There is a LOW potential for some
MVFR stratus around FL025, especially at D/FW, DAL, and GKY. At
this time, however, it appears more probable that convection will
slide southward, disrupting low level stratus transport northward
into Metroplex Terminals. Most hi-resolution model guidance
suggests that convection will survive its trek south of the Red
River. This would potentially impact both the Bonham and Bowie
cornerposts if the coverage of convection evolves as currently
thought. Convection should slowly slide towards the I-20 corridor
between 0900 and 1000 UTC on Thursday and persist through around
1300 UTC. Confidence in thunder near the TAFs is highest in the
0900 to 1300 UTC time frame and as a result, I went ahead and
included a mention of VCTS. TEMPO TS may be added to the TAFs
later depending on morning radar observations. There will likely
be some erratic wind shifts/wind speeds in and around storms as
well as MVFR cigs/reduced vis, but confidence isn`t high enough to
add this detail in the TAF at this time.

Showers and storms should wane quickly as winds around
FL025-FL030 veer quickly and weaken. With regards to surface wind
speed and direction, surface winds should remain elevated enough
to mitigate any potential non-convective LLWS at area terminals
during the overnight hours. After convection exits, surface winds
will slowly back in response to broad troughing to the northwest.

For the Waco TAF site---Waco should generally remain on the
precipitation-free side of the activity with the main concerns
being breezy nocturnal surface winds of up to 15 knots (some gusts
to near 20 knots possible) and MVFR stratus. This MVFR stratus
should arrive near 0800 UTC Thursday and will be primarily near or
above FL025. Low level mixing should be enough to keep any cigs
below FL020 at a minimal. VFR should return during the mid to late
morning hour time period. We will need to monitor the evolution
of convection to the north. Should this activity slide farther
south than currently anticipated, there could be potential impacts
to the terminal in the form of brief wind shift and/or showers
and storms.



.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.



.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

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.



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




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