Severe Thunderstorm Warning 340, NWS Norman, OK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORMAN OK
911 PM CDT THU MAY 1 2008

.DISCUSSION...
TWEAKS TO WIND AND FRONTAL TIMING TONIGHT AND TOMORROW MORNING.
BEST CHANCES FOR STORMS OVERNIGHT WILL BE NORTHERN PARTS OF
OKLAHOMA AS STRONG CONVERGENCE OCCURS ALONG FRONT. NEW LOCAL RUN
OF WRF KEEPS ACTIVITY NEAR/NORTH OF KANSAS BORDER...BUT WITH
MOISTURE AND COOLING ALOFT ACCOMPANYING FRONT...WE WILL KEEP
RELATIVELY HIGH POPS AS FAR SOUTH AS I-40. ALTHOUGH DISCRETE CELLS
POSSIBLE FOR A FEW MORE HOURS...STRONG LINEAR FORCING WILL LIKELY
LEAD TO SQUALL-LINE FORMATION.

&&

.PREV DISCUSSION... /ISSUED 230 PM CDT THU MAY 1 2008/

DISCUSSION...
THE LARGER SCALE PERSPECTIVE FOR TONIGHTS WEATHER HAS NOT CHANGED
MUCH FROM EARLIER. THE MOST WESTWARD OF TWO SMALL MID/UPPER LOWS
OVER THE CENTRAL ROCKIES IS CURRENTLY PIVOTING THROUGH THE BASE OF A
BROADER SCALE TROUGH OVER THE FOUR CORNERS REGION WHICH IS
MAINTAINING AN AXIS OF LARGER PRESSURE FALLS OVER THE OKLAHOMA
PANHANDLE. AN ASSOCIATED COLD FRONTAL BOUNDARY NEAR A LINE FROM
MEDFORD TO SEILING HAS STALLED WHILE THE DRYLINE HAS BECOME SLIGHTLY
MORE DISCERNIBLE FROM PERRY...TO EL RENO...AND WAURIKA. A 20Z
BALLOON FROM KOUN WILL BE RELEASED SHORTLY. IN THE MEANTIME...
SATELLITE AND PROFILER/METARS TRENDS CONTINUE TO INDICATE SHALLOW
MOISTURE AND A MODEST CAP.

ISOLATED CONVECTION REMAINS UNLIKELY BUT POSSIBLE ANYWHERE NEAR THE
DRYLINE THROUGH MID EVENING...BY WHICH TIME THE DRYLINE SHOULD HAVE
RETREATED IN RESPONSE TO THE APPROACHING UPPER LOW. MEANWHILE...THE
STALLED FRONT OVER NORTHERN OKLAHOMA SHOULD RESUME A SOUTHWARD
MOVEMENT TOWARD THE DRYLINE AND INTO A DEEPENING MOIST WARM SECTOR.
OUR GREATEST CONCERN FOR SEVERE THUNDERSTORMS IS THIS EVENING AS THE
DRYLINE RETREATS TOWARD THE REORGANIZING COLD FRONT OVER NORTHWEST
OR NORTH CENTRAL OKLAHOMA...WHICH IS WHEN INSTABILITY WILL
HIGHEST...CONVECTIVE INHIBITION LOWEST...AND VERTICAL WIND PROFILES
MOST SUPPORTIVE OF SUPERCELLS.

AFTER MIDNIGHT...WE STILL ANTICIPATE THAT THE CONVECTIVE MODE WILL
GRADUALLY TRANSITION AWAY FROM SUPERCELLS AND MORE TOWARD
MULTICELLS...INCLUDING A SQUALL-LINE...ESPECIALLY EAST OF INTERSTATE
35.

ASIDE FROM THE ABOVE MENTIONED SEVERE WEATHER CONCERNS...HIGH BASED
SHOWERS ARE FORMING NEAR DEEPER PORTIONS OF A BAROCLINIC ZONE NEAR
THE KANSAS/COLORADO BORDER. A LOCAL RUN OF THE WRF ARW SHOWS THESE
SHOWERS REACHING THE KANSAS/OKLAHOMA BORDER NORTH OF WOODWARD
BETWEEN 22 AND 24Z...WITH A SMALL RISK OF SHORT TERM/HIGH WIND
POTENTIAL. WILL HAVE TO MONITOR CLOSELY.

AFTER TONIGHT...THE GRIDDED FORECAST RESEMBLES THE GFS AND
ASSOCIATED MAV MOS...WHICH SHOW A SIGNIFICANT DRY AND COOLER PERIOD
BEGINNING FRIDAY AND CONTINUING THROUGH THE WEEKEND...BY WHICH TIME
THE GFS...WHICH AGREES WITH THE LARGER SCALE MESSAGE OF THE GFS
ENSEMBLE MEAN AND ECMWF...DEVELOPS A SPLIT-FLOW PATTERN AND CONTINUES
IT THROUGH MIDWEEK...SUGGESTING A DIFFICULT FORECASTING PERIOD
BEGINNING NEXT WEEK...WITH CHANCES OF CONVECTION RETURNING TO THE
REGION WITH THE DETAILS HIGHLY UNCERTAIN.

&&

.PRELIMINARY POINT TEMPS/POPS...
OKLAHOMA CITY OK  54  71  43  65 /  30  10  10  10
HOBART OK         51  75  41  68 /  10   0  10  10
WICHITA FALLS TX  57  80  45  71 /  10  10  10  10
GAGE OK           43  66  36  65 /  10   0  10  10
PONCA CITY OK     54  68  41  67 /  70  10  10   0
DURANT OK         65  76  53  69 /  20  20  10  10

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...WIND ADVISORY UNTIL 11 PM CDT THIS EVENING FOR
     OKZ004-005-009- 010-014>016-021-022.

TX...NONE.

&&

22/11

HAZARDOUS WEATHER OUTLOOK...UPDATE
NATIONAL WEATHER SERVICE NORMAN OK
935 PM CDT THU MAY 1 2008

OKZ004>048-050>052-TXZ083>090-021200-
HARPER-WOODS-ALFALFA-GRANT-KAY-ELLIS-WOODWARD-MAJOR-GARFIELD-NOBLE-
ROGER MILLS-DEWEY-CUSTER-BLAINE-KINGFISHER-LOGAN-PAYNE-BECKHAM-
WASHITA-CADDO-CANADIAN-OKLAHOMA-LINCOLN-GRADY-MCCLAIN-CLEVELAND-
POTTAWATOMIE-SEMINOLE-HUGHES-HARMON-GREER-KIOWA-JACKSON-TILLMAN-
COMANCHE-STEPHENS-GARVIN-MURRAY-PONTOTOC-COAL-COTTON-JEFFERSON-
CARTER-JOHNSTON-ATOKA-LOVE-MARSHALL-BRYAN-HARDEMAN-FOARD-WILBARGER-
WICHITA-KNOX-BAYLOR-ARCHER-CLAY-
935 PM CDT THU MAY 1 2008

THIS HAZARDOUS WEATHER OUTLOOK COVERS NORTHERN...WESTERN...
CENTRAL...AND SOUTHERN OKLAHOMA...AND WESTERN NORTH TEXAS.

.DAY ONE...TONIGHT...

THUNDERSTORM OUTLOOK...
THERE IS A MODERATE RISK FOR SEVERE THUNDERSTORMS OVERNIGHT IN A
PORTION OF CENTRAL AND NORTH CENTRAL OKLAHOMA. A SLIGHT RISK COVERS
LOCATIONS FARTHER WEST AND SOUTH THROUGH OKLAHOMA.

LOCATION...
THE MODERATE RISK AREA IS EAST OF A LINE FROM BLACKWELL TO SOUTHWEST
OKLAHOMA CITY. THE SLIGHT RISK INCLUDES THE REST OF THE AREA EAST OF
A LINE FROM CHEROKEE...HINTON...AND WAURIKA.

TIMING...
SEVERE THUNDERSTORMS ARE EXPECTED IN NORTHERN OKLAHOMA BEGINNING
AFTER 10 PM...AND SPREADING SOUTH AND EAST THROUGH EARLY MORNING.

IMPACTS...
A COMBINATION OF SUPERCELLS AND BOWING LINES IS EXPECTED OVERNIGHT.

LARGE HAIL MAY PEAK NEAR THE SIZE OF TENNIS BALLS WITH ANY
SUPERCELLS...BUT WILL GENERALLY AVERAGE CLOSER TO GOLF BALL SIZE
WITH MOST STORMS.

EXTREME THUNDERSTORM WIND GUSTS MAY REACH 75 MPH.

TORNADOES ARE POSSIBLE WITH ANY STRONG UPDRAFT THAT CAN REMAIN NEAR
THE LEADING EDGE OF STORM OUTFLOW.

RECOMMENDED ACTIONS...
STORM SPOTTER GROUPS AND EMERGENCY MANAGEMENT PERSONNEL IN THE
MODERATE RISK AREA SHOULD EXPECT SEVERE WEATHER OVERNIGHT. GROUPS IN
THE SLIGHT RISK AREA SHOULD BE PREPARED TO ACTIVATE IF NECESSARY.

DISCUSSION...
A STRONG COLD FRONT WILL ENCOUNTER DEEP GULF MOISTURE...WHILE A
STRONG UPPER LEVEL TROUGH WILL MAINTAIN DEEP LIFT AND COLD AIR
ALOFT. THUNDERSTORMS ARE EXPECTED TO BREAK OUT ALONG THE FRONT IN
NORTHERN OKLAHOMA...AND THEN SPREAD TO THE SOUTH AND EAST. VERY
STRONG INSTABILITY AND VERTICAL WIND SHEAR WILL ALLOW FOR ROTATING
UPDRAFTS...AND A FEW SUPERCELLS ARE POSSIBLE. STRONG LIFT...AND THE
SURGING COLD FRONT WILL...HOWEVER...FAVOR THE DEVELOPMENT OF A
BROKEN SQUALL LINE WITH EMBEDDED BOW ECHOES. ALL OF THESE STORMS
WILL HAVE THE POTENTIAL TO PRODUCE SEVERE WEATHER. THE GREATEST
CONCERNS WILL BE DAMAGING WINDS...FOLLOWED BY LARGE HAIL. TORNADOES
CANNOT BE RULED OUT...THOUGH...ESPECIALLY WITH ANY STORMS THAT
REMAIN ISOLATED...OR CAN MOVE OUT AHEAD OF THE COLD FRONT.

PROBABILITY TABLE...
VALID THROUGH 700 AM CDT FRIDAY MAY 2.
PROBABILITY OF THUNDERSTORMS OCCURRING IN THE
              NWS NORMAN COUNTY WARNING AREA...100 PERCENT.
PROBABILITY OF SEVERE STORMS IF STORMS OCCUR...90 PERCENT.

OTHER HAZARDOUS WEATHER...
STRONG WIND GUSTS OVER 45 MPH WILL OCCUR BEHIND THE COLD FRONT IN
WESTERN OKLAHOMA. WIND SPEEDS WILL DIMINISH SOMEWHAT AFTER
MIDNIGHT...BUT GUSTS OVER 40 MPH WILL STILL BE POSSIBLE THROUGH
CENTRAL OKLAHOMA AND INTO WESTERN NORTH TEXAS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY...

THUNDERSTORM OUTLOOK...
THUNDERSTORM CHANCES WILL RETURN TO THE SOUTHERN PLAINS EACH DAY
FROM MONDAY THROUGH WEDNESDAY. SEVERE WEATHER WILL BE POSSIBLE...
ESPECIALLY TUESDAY AND WEDNESDAY.

OTHER HAZARDOUS WEATHER...
NONE.

THE NEXT SCHEDULED HAZARDOUS WEATHER OUTLOOK WILL BE ISSUED AT 7 AM
FRIDAY.

11/BURKE

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