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

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FXUS64 KFWD 221739

Area Forecast Discussion
National Weather Service Fort Worth TX
1239 PM CDT Fri Sep 22 2017

An expansive stratus deck from this morning continues to
scatter out this afternoon due to good boundary layer mixing, and
all TAF sites had improved to VFR during the past hour. VFR
conditions will continue through the evening and into the
overnight hours. Stratus infiltration appears less likely for
Saturday morning due to weaker low level flow and some drying at
925 MB, so will leave out of the forecast at this time and monitor
trends tonight.

Otherwise, isolated showers will be possible this afternoon within
a strong warm/moist advection regime, but at this time it looks
like precip will remain west of North Texas TAF locations.



.UPDATE... /Issued 1144 AM CDT Fri Sep 22 2017/
Visible imagery indicates a nice moisture fetch extending from
the Western Gulf to the mid Texas Coast to Central Texas, due to
low level flow rounding the western side of a surface ridge
centered over the Southeast States. Convection is already ongoing
along the mid TX Coast, and some of the more recent high res
guidance is indicating the possibility of some of this convection
reaching our southwest counties early this afternoon and
eventually the western counties late afternoon, before dissipating
this evening. Slight chance POPs have therefore been added to
areas generally west of I-35/35W for this afternoon. Though an
isolated lightning strike cannot be ruled out, weather grids will
be limited to showers due to the weak forcing expected. The rest
of the forecast is in good shape.



.SHORT TERM... /Issued 326 AM CDT Fri Sep 22 2017/
Morning satellite imagery shows low cloud cover extending across
much of central Texas into North Texas thanks to abundant moisture
in the low levels of the atmosphere and a 30 kt low level jet.
These low clouds will continue to stream northward across the
region through the morning before scattering out around midday.
North Texas remains positioned between a deep trough over the
western U.S. and a weaker mid-level trough over the southeast.
This results in subtle ridging over the region with weak mid
level flow. Closer to the ground, a large surface anticyclone is
in place across much of the eastern U.S. and this will slowly
expand westward through the day. As a result, low level flow is
expected to remain more southerly or southeasterly with some drier
air moving in aloft from the east. Forecast soundings across the
region this afternoon feature modest mixing to around 800 mb with
only weak instability above. With the lack of any substantial
forcing, coverage of scattered showers or storms should be pretty
minimal (10% or less). It will still be warm today, although with
a more easterly component to the wind, we should see temperatures
a few degrees cooler than yesterday. Highs will still be in the
low to mid 90s areawide.



.LONG TERM... /Issued 326 AM CDT Fri Sep 22 2017/
/Saturday Onward/

After what has been a very dry September for the region, the final
week of the month will feature the highest rain chances we`ve seen
in quite a while. This will be due to the deep upper trough that
is currently taking up residence across the western US which will
begin to impact our weather during the first half of next week. In
the meantime however, we`ll be contending with continued above-
normal temperatures with little/no rain chances over the weekend.

As the upper trough continues to deepen to our west, our weather
will largely by controlled by an elongated upper ridge positioned
between the western trough and another weak upper low to our east.
The presence of the ridge is expected to result in warm and
mostly dry conditions for the forecast area both Saturday and
Sunday. Temperatures will remain above normal during this time,
but the deepening western trough will act to pull the thermal
ridge westward, keeping 850mb temperatures a bit cooler over our
forecast area. Highs should still be in the 90s for most locations
with lows in the upper 60s and 70s. With the warm advection
regime remaining in tact, we`ll keep the 60s and low 70s
dewpoints around, but heat index values should hold below 100F.
The strong forcing with the approaching trough will remain west of
our area over the weekend, along with the thunderstorm chances.

Changes will take place beginning on Monday as the trough and
its associated cold front approach from the northwest. Areas of
thunderstorms should be affecting a large portion of West TX
throughout this time as broad ascent east of the trough axis
generates widespread convection. We`ll begin to see increasing
cloud cover from this activity, and by Monday evening, a few
storms may approach our western counties. The front however, will
still be displaced well northwest of the area through the TX
Panhandle northeastward into KS.

On Tuesday, the front will make a push farther to the southeast
and should make it into North Texas by the end of the day. This
will mean increasing rain and thunderstorm chances especially for
areas along and west of I-35 through Tuesday night and into
Wednesday. As additional disturbances pivot through the larger
parent trough to our west, a few rounds of rainfall will be
possible from Wednesday into Thursday area-wide with the front
remaining draped through our forecast area. The meager lapse rates
overhead will result in very limited available instability. As a
result, the severe weather potential looks fairly low throughout
next week. However, PW values are expected to climb to near-
record values of over 2", and heavy rainfall/localized flooding
will probably be of greater concern. A bit of good news however is
the return of near or below normal temperatures through the
middle of the week, initially due to increased cloud cover and
later due to cooler air behind the slow-moving front. Highs will
likely be in the 70s or low 80s for most locations on Wed/Thu.

One potential caveat with this forecast lies in the timing, as
we`ve already begun to see some indications that guidance is
trying to slow the eastward movement of this system. This could
cause the timeline to be off by as much as 12-24 hours from the
current forecast. This is not uncommon with deeper cutoff lows,
which models are typically too impatient with in terms of how
quickly they advance eastward.

There is quite a bit of disagreement among operational models as
well as ensembles towards the end of the week, even with regards
to the larger scale synoptic features. As a result, have left some
lower rain chances through next Friday as the front may still be
lingering across Central TX. However, the front should move south
of the area next weekend resulting in moisture being scoured out
as far south as the Gulf of Mexico. This could mean a dry but
pleasant start to October, although would prefer to see some
consistency in guidance before getting too enthused about the
arrival of fall weather.



Dallas-Ft. Worth    92  75  95  75  94 /  10   5   5   5   5
Waco                92  72  94  70  93 /  20   5   5   5   5
Paris               89  71  92  70  90 /  10   5   5   5  10
Denton              91  72  93  71  93 /  10   5   5   5   5
McKinney            90  72  91  71  91 /  10   5   5   5   5
Dallas              92  76  95  76  94 /  10   5   5   5   5
Terrell             91  71  93  72  93 /  10   5   5   5   5
Corsicana           90  72  94  72  92 /  10   5   5   5   5
Temple              89  71  92  69  90 /  20   5   5   5   5
Mineral Wells       90  70  93  68  92 /  20   5   5   5   5




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