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Area forecast discussion...updated
National Weather Service Fort Worth Texas
641 am CDT Tue Sep 26 2017

12 UTC taf cycle

Concerns---shra potential and timing of wind shifts at metroplex
taf sites. Intermittent MVFR cig potential at Waco with subtle
wind shift.

For the metroplex taf sites---showers streamed northward overnight
and were efficient at producing some outflow which resulted in a
westerly wind shift for afw and ftw. Winds at these taf sites will
be out of the northeast before becoming more southeasterly by
mid-morning. All other taf sites should remain in south flow
through the early evening hours. Previously it appeared that MVFR
stratus would invade from the south. However, given the weakening
surface pressure field in response to the slow moving frontal
boundary, strong winds necessary for stratus transport appears
unlikely and i've removed MVFR stratus from the forecast for this
morning. There will be a potential for some showers, mainly west
of the taf sites today. I'll continue with a mention of vcsh at
all metroplex tafs with lower confidence in occurrence farther
east (dal and gky). Impacts to western arrivals/departures are
possible due to the convection out across the Big Country.
Overall, the prospects for lighting in vicinity of metroplex tafs appear
low given that forecast profiles support mostly tropical like
showers. There could be some reduced visibility should showers
settle in over any of the terminals, but confidence is too low to
include this mention in the tafs at this time.

Otherwise, southerly winds will shift to the east and eventually
north-northeast with time as the aforementioned cold front slices
southward through the region and north flow appears probable
around 0300 UTC. There could be some Post-frontal shower
activity, especially at afw and ftw and i've continued a mention
of vcsh between 0300 and 0600 UTC. In the d/fw extended taf,
there's a low chance for some Post-frontal MVFR stratus, but
overall signals in model guidance are not high enough to warrant
inclusion at this time.

For the Waco taf site---i've gone with a more optimistic taf this
morning. At this time, it appears that Waco may be on the periphery
of some of the poorer flying conditions with MVFR and IFR more
probable to the west. I'll maintain a chance for intermittent MVFR
stratus around fl025 starting mid-morning and into the noontime
hour. If the configuration of stratus remains unchanged over the
next several hours, it's even possible that the mention of MVFR
may be removed all together. The potential for vcsh isn't quite as
high here at Waco given that a majority of the stronger forcing
appears to be to the northwest, but we'll need to monitor this
threat through the day. It appears that the frontal boundary will
become quite diffuse as it approaches the Waco taf site and i've
only shown a very subtle wind shift to the northeast as a result
late this evening and into the overnight hours.



Short term... /issued 218 am CDT Tue Sep 26 2017/
/today and tonight/

The main concern in the short term will be the placement of
highest rain and thunder chances. Widespread severe weather
appears unlikely given the modest lapse rates and limited deep
layer shear. Otherwise, it should feel slightly cooler for some
with widespread cloud cover and increasingly east and north winds.

For today---ongoing showers and embedded thunderstorms will
continue this morning as isentropic ascent along the 300k and 305k
Theta surfaces continues for areas west of the I-35 corridor.
These pockets of concentrated precipitation should diminish
through mid-morning and it's possible that for a short window of
time, much of the area remains mostly rain-free. Otherwise, patchy
fog across southeastern zones will gradually dissipate with
cloudy to partly sunny skies across north and central Texas.
Additional precipitation is expected to Blossom later this
afternoon, especially for areas near and west of the Highway 281
corridor. This precipitation will be in response to increasing
isentropic lift as well as the encroaching cold front currently
across the Texas rolling plains.

For tonight---the cold front will continue to slide southward
through central Texas through Wednesday morning. Ascent along and
behind the front will persist and will result in another good
rain shield, mainly near and west of the Highway 281 corridor. As a
result, i've kept highest pops out west with lower rain chances
farther east.



Long term... /issued 218 am CDT Tue Sep 26 2017/
/Wednesday through next Monday/

At the start of Wednesday, a cold front will be draped across
North Texas with the large upper trough still over the western
U.S. Persistent low level isentropic ascent will continue through
much of the day resulting in a good coverage of showers and a few
thunderstorms mainly west of I-35. Areas east of I-35 will be
under more of an influence from upper ridging and increasing
subsidence through the day. As we go through the day Wednesday
into Thursday, the large upper trough over the western U.S. Will
finally begin to slowly deamplify and eject eastward. As it does,
ridging will strengthen over North Texas leaving only the frontal
boundary as a primary focus for precipitation development. Rain
chances will generally be confined to areas west of I-35 Wednesday
night through Thursday night before diminishing areawide on
Friday. With the main trough moving through the plains on Friday,
a secondary push of cooler and noticeably drier air will slide
into North Texas late Friday evening. This should effectively end
precipitation chances for North Texas with the forecast remaining
dry into early next week.

Given weak mid level lapse rates and only weak instability during
peak heating, the overall severe weather threat Wednesday through
Friday looks minimal and we'll only mention isolated thunderstorms
in the forecast with showers prevailing. The bulk of the synoptic
forcing will remain over West Texas through Thursday, so even with
the cold front draped across the cwa, highest rain chances
Wednesday and Thursday will be west of I-35. Some locally heavy
rainfall amounts may occur across our far western counties with
areas along and east of I-35 likely receiving less than an inch of
rain through the week.

Temperatures will be warm across the eastern half of the region on
Wednesday but as the cold front slides farther south, temperatures
will continue to cool. Highs will be at or below seasonal normals
Thursday through the weekend.



Preliminary point temps/pops...
Dallas-ft. Worth 87 73 86 68 82 / 30 30 30 20 20
Waco 89 72 88 70 86 / 40 20 20 30 20
Paris 87 70 87 68 82 / 10 10 20 20 20
Denton 86 70 83 65 79 / 50 30 30 20 20
McKinney 87 71 86 67 80 / 30 30 20 20 20
Dallas 89 74 87 70 82 / 30 30 20 20 20
Terrell 88 71 90 69 85 / 20 10 20 20 20
Corsicana 89 71 89 71 87 / 20 10 20 20 20
Temple 87 71 86 70 85 / 40 30 30 30 20
Mineral Wells 83 68 80 63 77 / 60 60 50 40 40


Forward watches/warnings/advisories...

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