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Area forecast discussion
National Weather Service Fort Worth Texas
308 am CDT Mon Sep 25 2017

Short term...
/today and tonight/

The main forecast concern through tonight will be ever slowly
increasing rain chances mainly west of I-35. Water vapor imagery
shows a large upper trough extending over much of the western U.S.
And into Texas this morning. This large trough has several smaller
embedded vorticity maxima which will rotate through the main
trough over the next several days.

For today, most of the shower and thunderstorm activity will
remain well west of our area. A persistent band of low and mid
level isentropic ascent will be in place across West Texas
extending northward into western Oklahoma and Kansas. This area
is also on the eastern periphery of stronger forcing from the main
upper trough. Showers and thunderstorms should increase in
coverage through the day as stronger forcing for ascent spreads
through West Texas. We may see some of this activity move into our
far western counties later this afternoon and we'll have the
highest pops generally west of a Bowie to Lampasas line. Lapse
rates are unimpressive and overall instability is weak through
tonight across the region, so the severe weather threat will be
low. Winds fields are modest for this time of year though and
oriented in a way that would support training convection. This is
most likely to occur west of our area, but nonetheless does bear
watching. Any training convection could produce locally heavy
rainfall. Temperatures today will continue to be several degrees
above normal and could be impacted by increasing cloud cover.
We'll still be looking at highs in the upper 80s and lower 90s

Eastward progression of the upper trough is expected to be slow
and the main cold front associated with this system is expected to
only make slow southward progress into Oklahoma overnight
tonight. This means the best rain chances will remain well west of
I-35 through tonight.



Long term...
/Tuesday Onward/

The deep upper low across the western US will remain there
through midweek, generating multiple waves of showers and
thunderstorms across eastern New Mexico and West Texas. In
addition, its associated cold front will slowly approach North
Texas and will eventually increase our rain chances Wednesday
through Friday. However, the most widespread rainfall and highest
totals are expected to remain west of the forecast area. Increased
cloud cover and cooler air behind a pair of fronts will result in
some cooler (near normal) temperatures, especially for the end of
the week and the upcoming weekend.

On Tuesday, the front should still be located just west-northwest of the
forecast area, draped roughly from San Angelo to Oklahoma City.
Widespread showers and a couple thunderstorms should be ongoing
along this axis of increased lift, some of which will drift into
our western counties Tuesday afternoon and evening. As activity
moves east however, it will slowly decay as it outruns forcing
from both the front and broad ascent ahead of the upper trough.
Lapse rates will also be very meager, and much of the rain
showers may be lightning-free due to the lack of
instability/forcing. As will be the case for much of the week,
locations west of I-35 will have the highest rain chances, with
some spots to the east remaining hot and mostly dry.

Similar trends should be expected on Wednesday, although by this
time, the slow-moving front will have finally drifted into North
Texas. This front should bisect the forecast area into a cooler
and rainy western half with a continued warm and mostly dry
eastern half. Despite the front being in the vicinity, we'll still
be lacking upper dynamic forcing as the trough will begin
retrograding westward with upper ridging building in to take its
place. As a result, there will be a battle between lift from weak
convergence along the front against some broad subsidence from
building heights aloft. This should act to limit the extent of
shower/thunderstorm activity through Wednesday and even into
Thursday with the highest rain chances continuing to be west of
I-35. A similar setup should still exist on Thursday with the
front moving just slightly farther southeast, but still positioned
within the forecast area. Since rain rates/amounts are expected
to remain on the lighter side, am not anticipating much in the
way of heavy rain or flooding issues at this point; these
concerns should be confined to locations west of the forecast

Rain chances will begin tapering off to the south on Friday as
the front finally sinks southward. This will be due to flow aloft
becoming more zonal, causing the ejecting shortwave to allow a
secondary push of cooler and drier air to move southward through
the plains. Lingering showers and a few storms will be possible
through central Texas most of the day Friday, while rain chances
shut down across North Texas with the arrival of drier air. This
scenario would mean a fairly pleasant early fall weekend for most
of the region with temperatures near normal and mostly dry



Aviation... /issued 1143 PM CDT sun Sep 24 2017/
isolated showers west of a k0f2-klzz line should continue to
diminish through 08z. The best lift associated with an upper level
trough over the western U.S. Will remain across West Texas.
As a shortwave lifts northeast out of the main trough, isolated
to scattered showers and maybe a few thunderstorms will be
possible late Monday morning through the afternoon and evening
hours mainly west of a k0f2-klzz line.

Expect mostly VFR conditions at the metroplex taf sites through
12z Tuesday. At Waco, expect MVFR ceilings to spread into the area
10-12z with an improvement to VFR 16-17z. Southeast winds around
10 knots will veer around to the south by 12z.



Preliminary point temps/pops...
Dallas-ft. Worth 92 74 91 73 86 / 5 10 30 20 40
Waco 91 72 91 72 87 / 10 10 30 30 30
Paris 90 69 90 70 88 / 10 5 20 10 20
Denton 90 72 88 69 82 / 10 10 40 30 40
McKinney 89 71 91 71 85 / 5 5 20 20 30
Dallas 92 75 92 74 87 / 5 5 30 20 30
Terrell 90 71 92 72 88 / 5 5 20 10 20
Corsicana 91 71 92 72 90 / 5 5 20 10 20
Temple 89 71 88 71 86 / 10 10 30 30 30
Mineral Wells 89 70 85 66 78 / 20 30 50 50 50


Forward watches/warnings/advisories...

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