Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 200500
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
1200 AM CDT Fri Oct 20 2017

...Updated Aviation Discussion...

&&

.AVIATION...
For the 06z TAFs:

Stratus will develop later tonight across portions of Texas and
affect southwest sites by around sunrise with MVFR conditions.
Short term model guidance trends suggest ceilings further
northeast into central and northern Oklahoma may be VFR for much
of the day before lowering at all locations by evening. IFR
conditions seem quite possible Friday evening into the night.
South winds will strengthen throughout the day and be considerably
higher than previous days.

&&

.PREV DISCUSSION... /issued 405 PM CDT Thu Oct 19 2017/

DISCUSSION...
Primary forecast issue is the risk for severe thunderstorms on
Saturday.

For late tonight into tomorrow, a shortwave that is currently
located across the Texas/New Mexico border is expected to lift
northeastward into western north Texas and Oklahoma. There will be
a low chance of showers/storms from wave, but severe weather is
not expected. Isentropic ascent/warm advection tomorrow night into
Saturday will result in a continued low chance of showers/storms.

By Saturday afternoon, a mid/upper-level trough will eject into
the Plains. Along the southern periphery of trough, a secondary
mid-level jet/vorticity maxima will rotate around the base of the
shortwave trough. In response to an embedded jet streak, a
surface low may develop across southwest Oklahoma and adjacent
parts of north Texas.

The attendant cold front will enter northwest Oklahoma Saturday
afternoon. Thunderstorms are expected to develop along the cold
front late afternoon through the evening. The environment will be
more than sufficient for severe thunderstorms with effective bulk
shear >50 knots and MLCAPE >2000 J/kg. Any discrete thunderstorms
could become superceullar with the given parameter space. If a
surface low develops, localized backing of surface winds would
increase the low-level shear and the attendant tornado threat.
Thunderstorms are expected to grow upscale into a quasi-linear
convective system due to strong forcing along the cold front.

The greatest uncertainty is the timing/speed of the cold front.
The 19/12Z NAM and 3 KM NAM are much faster with the cold front
than the 19/12Z GFS. Even the ECMWF is slightly faster than the
GFS. The faster solution would likely lead toward thunderstorms
becoming undercut by the cold front, which would mitigate the
spatiotemporal extent of any higher end severe/tornado risk;
however, damaging wind gusts will be still be a hazard along the
line of thunderstorms. For now, will trend the forecast toward the
faster solution based on the surface pressure bulge.

In the front`s wake, cooler and drier air will advect into the
region for Sunday. Sunday will be much cooler with highs in the
mid-60Fs to low 70Fs.

A brief warm-up is expected Monday afternoon before another cold
front passes by late Monday. A dry frontal passage is expected due
to limited moisture. Cooler weather with highs in the 60Fs are
expected Tuesday and Wednesday behind this front. Some locations
may have lows in the 30Fs by Wednesday morning.

Mahale

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  78  59  76  67 /   0   0  20  20
Hobart OK         79  61  76  65 /   0  10  20  20
Wichita Falls TX  81  61  78  68 /   0  10  20  10
Gage OK           78  60  73  63 /   0   0  20  20
Ponca City OK     79  58  77  68 /   0   0  20  20
Durant OK         81  58  78  67 /   0  10  20  20

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...None.
TX...None.
&&

$$

12/03


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