Tornado Warning 37, NWS Norman, OK

OKZALL-311200-

OKLAHOMA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE OKLAHOMA CITY OK
100 PM CDT WED MAY 30 1990

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
EVENING OVER THE EASTERN HALF OF OKLAHOMA.  THE MAIN THREAT AREA
IS EAST OF A LINE FROM ARDMORE TO OKLAHOMA CITY TO ALVA.

EARLY THIS AFTERNOON...A SURFACE LOW WAS CENTERED OVER NORTHWEST
OKLAHOMA WITH A TROUGH EXTENDING SOUTH INTO THE SOUTHWEST PART OF
THE STATE.  THE AIRMASS EAST OF THE TROUGH WAS WARM MOIST AND
MODERATLY UNSTABLE...AND THE AIRMASS IS EXPECTED TO BECOME MORE
UNSTABLE LATER THIS AFTERNOON AS THE SUN BEGINS TO BREAK THROUGH
THE CLOUDS AND SURFACE TEMPERATURES BEGIN TO WARM.

ALOFT...AN UPPER LEVEL LOW PRESSURE SYSTEM WAS CENTERED OVER
SOUTHWEST KANSAS.  THE UPPER LEVEL LOW WILL TRACK EAST ALONG THE
KANSAS-OKLAHOMA BORDER THIS AFTERNOON.  WEAK DISTURBANCES ROTATING
AROUND THE LOW MAY ACT AS TRIGGERS FOR THUNDERSTORM DEVELOPMENT
IN THE WARM AND INCREASINGLY UNSTABLE AIRMASS OVER THE CENTRAL AND
EASTERN OKLAHOMA.

THE THREAT OF SEVERE WEATHER WILL DECREASE TONIGHT AS THE UPPER LEVEL
LOW MOVES OFF TO THE EAST AND THE LOWER LEVELS OF THE ATMOSPHERE
COOL AFTER SUNSET.

CIVIL DEFENSE AND STORM SPOTTER GROUPS IN CENTRAL AND EASTERN OKLAHOMA
SHOULD REMAIN ALERT AND BE READY FOR ACTIVATION IF NECESSARY THIS
AFTERNOON AND EVENING.

LOCAL STORM REPORT
NATIONAL WEATHER SERVICE OKLAHOMA CITY OK
245 PM CDT WED MAY 30 1990

...ADDITIONAL REPORT FROM TUESDAY EVENING MAY 29TH...

TIME       COUNTY      REPORT
1030 PM    CLEVELAND   NUMEROUS LARGE TREE LIMBS WERE DOWNED...SEVERAL
                       LARGE TREES WERE UPROOTED AND MINOR DAMAGE TO
                       FENCES AND ROOFS OCCURRED IN WEST NORMAN.
                       EXAMINATION OF THE AREA BY NATIONAL WEATHER
                       SERVICE PERSONNEL INDICATED A SMALL DOWNBURST
                       OF STRAIGHT-LINE WINDS WAS RESPONSIBLE FOR THE
                       DAMAGE.

OKZALL-310200-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE OKLAHOMA CITY OK
345 PM CDT WED MAY 30 1990

...COLD AIR FUNNELS AND VERY WEAK TORNADOES POSSIBLE IN NORTHERN
   OKLAHOMA THIS AFTERNOON...

A VIGOROUS UPPER LEVEL TROUGH OF LOW PRESSURE MOVED THROUGH SOUTHERN
KANSAS THIS MORNING AND WAS OVER SOUTHEASTERN KANSAS EARLY THIS
AFTERNOON. IN THE LOWER LEVELS OF THE ATMOSPHERE...HOWEVER...A
WELL DEFINED LOW PRESSURE SYSTEM WAS CENTERED ALONG THE KANSAS
BORDER NORTH OF ALVA. SATELLITE IMAGERY SUGGESTS THAT THIS LOW PRESSURE
SYSTEM IS MOVING SLOWLY TOWARD THE EAST-SOUTHEAST TOWARD NORTH CENTRAL
OKLAHOMA. THE LOW SHOULD BECOME NEARLY STATIONARY AND WEAKEN THIS
EVENING AS A LOW PRESSURE TROUGH BEGINS TO INTENSIFY IN THE LEE OF THE
ROCKY MOUNTAINS.

THE ATMOSPHERE IS NEARLY SATURATED AND MARGINALLY UNSTABLE OVER NORTH
CENTRAL AND NORTHEASTERN OKLAHOMA EARLY THIS AFTERNOON. THE DENSE CLOUD
COVER WHICH PREVAILED ACROSS MUCH OF THE STATE GRADUALLY HAS BEEN
ERODING EASTWARD. THE MID AND UPPER LEVELS OF THE ATMOSPHERE REMAIN
RELATIVELY COOL OVER THIS AREA. SURFACE HEATING HAS ENHANCED
INSTABILITY...AND CONVERGING LOW LEVEL WINDS IN THE VICINITY OF THE
LOW PRESSURE SYSTEM HAVE ACTED AS A FOCUSING MECHANISM FOR THE
DEVELOPMENT OF SCATTERED THUNDERSTORMS.

THE TENDENCY OF THE LOW LEVEL WINDS TO ROTATE IN THE VICINITY OF THE
LOW PRESSURE SYSTEM HAVE PROVIDED AN ENVIRONMENT FAVORABLE FOR THE
DEVELOPMENT OF SMALL SCALE ROTATION IN THE VICINITY OF THE THUNDER-
STORMS. THE NEARLY SATURATED STATE OF THE ATMOSPHERE WILL CAUSE THESE
WEAK SMALL SCALE FEATURES TO DEVELOP INTO VISIBLE FUNNELS. MOST OF
THE FUNNELS WILL NOT TOUCH DOWN...AND ANY WHICH DO WILL PRODUCE ONLY
MINOR DAMAGE. THE SHORT-LIVED AND SMALL SCALE CHARACTERISTICS OF THESE
FEATURES MAKE EARLY DETECTION BY DOPPLER OR CONVENTIONAL RADAR
EXTREMELY DIFFICULT...AND ACHIEVING ANY WARNING LEAD TIME IS NEARLY
IMPOSSIBLE.

PERSONS IN NORTHERN OKLAHOMA ARE URGEKD TO BE ALERT TO THE POSSIBILITY
OF FUNNEL CLOUDS AND VERY WEAK TORNADOES AND TO PREPARE TO TAKE
COVER IF THREATENING WEATHER APPROACHES. THE NATIONAL WEATHER SERVICE
WILL MONITOR THE THUNDERSTORMS CAREFULLY AND ISSUE WARNINGS WHENEVER
POSSIBLE.