Severe Thunderstorm Warning 865, NWS Norman, OK

Area Forecast Discussion...UPDATED
National Weather Service Norman OK
854 PM CDT Wed Sep 20 2017

.UPDATE...
Increased storms chances through the night near stalled frontal
boundary as modest low level jet increases. Still quite unstable
so cannot rule out a brief severe storm as activity builds
northward.

&&

.PREV DISCUSSION... /issued 600 PM CDT Wed Sep 20 2017/

DISCUSSION...
The 00Z aviation discussion follows....

AVIATION...
Thunderstorms have formed late this afternoon over parts of
central and northern Texas. It is possible, but so far unlikely,
that storms will affect KSPS between 00Z and about 03Z. Later, the
nocturnal low-level jet, plus mid-level moisture, plus weak
isentropic lift, could generate a few showers or thunderstorms
after 06Z and before about 18Z over roughly the western 2/3 of
Oklahoma and adjacent parts of Texas. Again, chances are low, but
certainly not zero.

Winds will decrease with sunset, then rapidly increase again
tomorrow within an hour or two after sunrise. There could be a
brief period of significant low-level wind shear near KLTS-KJWG-
KPNC, but model indications are not as strong as the previous
forecast.

Finally, low clouds may form over eastern
Texas and eastern Oklahoma early Thursday. Forecast wind
trajectories and current moisture levels over Texas, however,
suggest that ceilings should remain well east/southeast of our TAF
sites.

CmS

PREV DISCUSSION... /issued 350 PM CDT Wed Sep 20 2017/

DISCUSSION...
A surface front that stalled over western Oklahoma today will
retreat/weaken overnight, leaving all of Oklahoma (at least east
of the Panhandle) and north Texas in the warmer airmass for
tomorrow and Friday. The heat and humidity will allow for at least
isolated thunderstorms each day, depending on cap strength.

For the remainder of this afternoon and early this evening, the
greatest chance for thunderstorms will be over north-central
Oklahoma...and in our Texas counties + adjacent parts of southwest
Oklahoma. The cap will be weakest in these locations, and weak
low-level convergence combined with high temperatures may be
enough to generate a few storms despite the cap. If storms do
develop, strong winds would be the primary threat. Forecast
upper-air soundings suggest a hail threat, although the high
freezing level would help reduce that threat somewhat.

A strand of mid-level moisture along the nocturnal low-level jet,
amid weak isentropic lift, may generate a few showers and
thunderstorms over parts of western/central Oklahoma (and adjacent
parts of north Texas) Thursday morning. Then, the afternoon
situation resembles today's, with a continuing chance of isolated
thunderstorms.

The hot weather, breezy conditions, and small area of relatively
low humidities will cause "Elevated" fire danger conditions for
the next several afternoons across far northwest Oklahoma.

By Friday, mid-level temperatures should be warm enough to
preclude any significant chance of storms, but the weekend will
see the approach of a large-scale trough. This will bring
increasing chances for rain and thunderstorms. A slight chance
will begin Saturday in the far northwest, then chances will
increase and spread east Sunday into Monday.

For Tuesday onward, there is significant model spread, so we have
rain chances in the forecast, but with substantial uncertainty.

This progression of weather systems will result in a gradual
decrease in afternoon temperatures through the period.

CmS

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  75  91  71  89 /  20  20  10  10
Hobart OK         72  94  72  91 /  20  20  20   0
Wichita Falls TX  76  95  73  92 /  30  20  10   0
Gage OK           63  95  71  90 /   0  10  10   0
Ponca City OK     75  92  73  91 /  30  20  10   0
Durant OK         75  91  72  91 /  10  10  10  10

&&

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

11/26

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE Norman OK
728 PM CDT WED SEP 20 2017

OKZ037-TXZ085-086-210100-
Tillman OK-Wichita TX-Wilbarger TX-
728 PM CDT WED SEP 20 2017

...SIGNIFICANT WEATHER ADVISORY FOR southeastern Tillman...
northwestern Wichita and east central Wilbarger Counties Until 800 PM
CDT...

AT 727 PM CDT, a strong thunderstorm was located 10 miles northeast
of Harrold, moving northeast at 15 MPH.

HAZARDS INCLUDE...
Wind gusts to 50 MPH...

Locations impacted include...
Grandfield, Hollister and Loveland.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Monitor the weather situation closely and be alert for threatening
weather conditions.

&&

LAT...LON 3408 9887 3418 9905 3445 9887 3426 9861
TIME...MOT...LOC 0027Z 220DEG 13KT 3418 9890

11

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE Norman OK
850 PM CDT WED SEP 20 2017

TXZ086-210215-
Wichita TX-
850 PM CDT WED SEP 20 2017

...SIGNIFICANT WEATHER ADVISORY FOR central Wichita County Until 915
PM CDT...

AT 849 PM CDT, a strong thunderstorm was located 6 miles west of Iowa
Park, moving east at 20 MPH.

HAZARDS INCLUDE...
Hail up to the size of nickels...
Wind gusts to 50 MPH...

LAT...LON 3393 9883 3402 9885 3413 9859 3393 9853
TIME...MOT...LOC 0149Z 258DEG 16KT 3398 9878

..speg.