Severe Thunderstorm Warning 848, NWS Norman, OK

Area Forecast Discussion
National Weather Service Norman OK
331 AM CDT Tue Sep 19 2017

.DISCUSSION...
Elevated thunderstorms are ongoing across north central Oklahoma
this morning. This convection appears to be associated with warm
air advection/isentropic ascent that is augmented by a low-level
jet. Latest HRRR suggests the storms will continue shifting
eastward across north central Oklahoma the next few hours. Kept a
mention of storms through 14Z to account for this.

For this afternoon, a subtle shortwave trough is expected to
initiate isolated thunderstorms across western north Texas and
adjacent parts of southwest Oklahoma as convective inhibition is
forecast to be minimal.

Environmental conditions will be favorable for isolated strong to
severe thunderstorms with MLCAPE >= 2500 J/kg and effective bulk
shear up to 20 knots. A dry subcloud layer with forecast DCAPE >=
1500 J/kg indicates damaging wind gusts will be greatest hazard.
Steep mid-level lapse rates and ~1000 J/kg of CAPE between -10C
to -30C suggest hail will also be a potential hazard with any
stronger updrafts.

Fire weather conditions will also be an issue this afternoon. A
strong pressure gradient (~11 mb between Durant and Buffalo) and a
relatively deep mixed-layer will result in a breezy day--especially
across the western half of Oklahoma. Opted to increase wind speeds
above blended guidance. The combination of temperatures in the
mid-90Fs, relative humidity <35%, and sustained wind speeds >=25
mph will result in near critical fire weather conditions across
western Oklahoma. Issued a Fire Danger Statement based on this
assessment.

By Wednesday, a shortwave trough is expected to pass by the
Northern Plains. The attendant cold front is expected to enter
northwest Oklahoma Wednesday afternoon, which will cool
temperatures slightly across the northwest; however, for most
locations, hot temperatures (~10F above average) will prevail.
Temperatures might even be a littler hotter than on Tuesday with a
low-level thermal ridge ahead of the front. The surface trough
associated with the front should relax the pressure gradient
substantially tomorrow afternoon, which will lower wind speeds and
temper fire weather conditions. The greatest ascent for any
convection along the front will likely stay to the north of
Oklahoma. Therefore, opted to only have a slight chance near the
Kansas/Oklahoma border. The cold front will return back north as a
warm front Wednesday night.

For Thursday afternoon, another breezy day is expected as the
surface pressure gradient increases due to lee cyclogenesis.
Temperatures will return to the mid-90Fs across northwest
Oklahoma. Elsewhere, hot temperatures will continue. Once again,
near critical fire weather conditions will be possible--especially
across northwest Oklahoma with a return to gusty, southerly
winds.

For Friday and Saturday, very warm and dry weather will continue as
the Southern Plains will be on the western periphery of a mid-level
ridge centered across the Midwest. High temperatures might be
slightly cooler with the low-level thermal ridge shifting
northward ahead of cold front in the Central Plains. Even so, high
temperatures will be above average in the upper 80Fs to low 90Fs.

By Sunday night into Monday, the GFS and ECMWF both indicate than
the longwave trough across the western contiguous United States
will slowly shift eastward with approach of another trough across
the Eastern North Pacific. Combined with tropical moisture from
the Pacific, this will become a favorable pattern for widespread
showers/storms. Locally heavy rainfall may become a hazard during
this period. Abundant cloud cover/precipitation should also lower
high temperatures to near average by Monday. This unsettled/wet
pattern may persist beyond this forecast period.

Mahale

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  92  75  94  74 /  10  10  10  10
Hobart OK         94  72  96  73 /  20  20   0  10
Wichita Falls TX  97  75  98  75 /  20  30   0  10
Gage OK           97  65  89  66 /  10   0  10  10
Ponca City OK     94  75  94  74 /  20  10  10  20
Durant OK         93  75  93  73 /  10  10  10  10

&&

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

30/10

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE Norman OK
347 AM CDT TUE SEP 19 2017

OKZ012-013-190915-
Garfield OK-Noble OK-
347 AM CDT TUE SEP 19 2017

...SIGNIFICANT WEATHER ADVISORY FOR northeastern Garfield and
northwestern Noble Counties Until 415 AM CDT...

AT 344 AM CDT, a strong thunderstorm was located 5 miles northeast of
Breckenridge, moving east at 30 MPH.

HAZARDS INCLUDE...
Hail up to the size of nickels...
Wind gusts to 40 MPH...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3659 9741 3636 9739 3635 9778 3658 9784
      3659 9753
TIME...MOT...LOC 0844Z 264DEG 25KT 3648 9766

30