DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 211729
SWODY2
SPC AC 211727

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1227 PM CDT SAT SEP 21 2013

VALID 221200Z - 231200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
A PROGRESSIVE...AMPLIFIED UPPER FLOW PATTERN WILL PERSIST ACROSS THE
LOWER 48 STATES THIS WEEKEND. IN THE WEST...A SPLIT FLOW REGIME
DEVELOPING LATE TODAY ALONG THE WEST COAST WILL SHIFT INLAND TOWARD
THE ROCKIES ON SUNDAY. A PACIFIC SHORTWAVE TROUGH LOCATED WITHIN
THE SRN BRANCH OF THE SPLIT FLOW IS FORECAST TO TRACK EWD FROM ERN
CA/NV...REACHING THE FOUR CORNERS BY 23/00Z AND THE CENTRAL/SRN HIGH
PLAINS BY 12Z MONDAY. MEANWHILE...FARTHER EAST...A LONGWAVE TROUGH
IS EXPECTED TO TRACK THROUGH NERN STATES AND QUEBEC...WITH THE SRN
EXTENT MOVING OFF THE MIDDLE/SRN ATLANTIC COASTAL REGIONS.

IN THE LOW LEVELS...A SURFACE LOW IS FORECAST TO DEVELOP IN VICINITY
OF THE FOUR CORNERS AS A PACIFIC COLD FRONT ADVANCES EWD REACHING
ERN UT/AZ BY LATE SUNDAY AFTERNOON. THIS FRONT WILL PROGRESS EWD
SUNDAY NIGHT IN TANDEM WITH THE ATTENDANT PACIFIC SHORTWAVE
TROUGH...AND SHOULD EXTEND FROM ERN CO TO ERN NM BY 12Z MONDAY.
MEANWHILE...A LEE TROUGH IS EXPECTED TO STRENGTHEN OVER THE HIGH
PLAINS...WITH THE NRN EXTENT SHIFTING EWD THROUGH WRN TO CENTRAL ND
AND WRN SD.

...FOUR CORNERS...
ISOLATED TO SCATTERED SHOWERS/TSTMS SHOULD BE ONGOING AT 12Z
SUNDAY...WITH THE LIKELIHOOD FOR COVERAGE TO BECOME NUMEROUS THROUGH
THE FORECAST PERIOD FROM WEST-EAST. THIS WILL OCCUR AS STRONG...AND
A SOMEWHAT COMPACT...CORRIDOR OF FORCING FOR ASCENT ATTENDANT TO THE
PROGRESSIVE SHORTWAVE TROUGH/COLD FRONT ADVANCES EWD THROUGH
UT...PARTS OF CENTRAL/ERN AZ INTO WRN/CENTRAL CO AND WRN/NRN NM.
SURFACE DEW POINTS WILL TEND TO BE IN THE 40S TO LOWER 50S INTO
SUNDAY AFTERNOON. DESPITE COOLING MIDLEVEL TEMPERATURES/STEEPENING
LAPSE RATES WITH THE APPROACH OF THE SHORTWAVE TROUGH...SURFACE DEW
POINTS IN THE 40S TO LOWER 50S WILL LIMIT THE DEVELOPMENT OF
STRONGER INSTABILITY. ALTHOUGH BUOYANCY SHOULD TEND TO BE MEAGER
/MUCAPE AOB 500 J PER KG/...ROBUST DCVA AND A STRONG HEIGHT
FALL/RISE COUPLET SUGGESTS A LINE OF STORMS WILL BE POSSIBLE ALONG
THE WIND SHIFT. A TRANSIENT SUPERCELL CANNOT BE RULED OUT...GIVEN
EFFECTIVE BULK SHEAR RANGING FROM 40-50 KT. MARGINALLY SEVERE HAIL
AND ISOLATED STRONG WIND GUSTS WILL BE THE PRIMARY THREATS WITHIN
THE 5 PERCENT SEVERE WEATHER THREAT AREA OF THE FOUR CORNERS. IF
LATER MODELS/OUTLOOKS INDICATE STRONGER DESTABILIZATION...THEN
HIGHER SEVERE PROBABILITIES COULD BE WARRANTED.

...CENTRAL HIGH PLAINS TO THE NRN PLAINS...
ABOVE-NORMAL SURFACE TEMPERATURES SHOULD CONTRIBUTE TO A
DEEPLY-MIXED BOUNDARY LAYER SUPPORTING ISOLATED HIGH-BASED STORMS
LATE SUNDAY AFTERNOON ALONG THE SURFACE TROUGH. THESE COULD GROW IN
COVERAGE...OR AT LEAST SPREAD/DEVELOP NWD AS THE LLJ STRENGTHENS
SUNDAY EVENING AMIDST MERIDIONAL DEEP-LAYER WIND PROFILES. ALTHOUGH
THE DEGREE OF SHEAR SHOULD REMAIN MODERATE /25-35 KT/...MULTICELL
STRUCTURES MAY BE CAPABLE OF LOCALIZED SEVERE WIND/HAIL.

..PETERS.. 09/21/2013

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