Severe Thunderstorm Warning 99, NWS Tulsa, OK

EASTERN OKLAHOMA/NORTHWEST ARKANSAS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TULSA OK
116 PM CDT SUN MAY 6 2001

SHORT WAVE JUST ENTERING WESTERN OKLAHOMA IS EXPECTED TO START
KICKING OFF SCATTERED THUNDERSTORMS ALONG BOUNDARY TO OUR WEST
WITH CONVECTION IN THE AREA LATE THIS AFTERNOON AND THIS EVE.
UNCERTAIN ABOUT CHC FOR PCP THIS EVE BEHIND MAIN AREA OF
CONVECTION THAT IS FCST TO MOVE INTO NW ARK/SE OK AFTER 0Z.
ETA/RUC/NGM/AVN ALL HINT AT ADDITIONAL DEVELOPMENT ALONG
COLD FRONT THAT WILL ENTER NE OK AROUND MIDNIGHT. MAIN AREA
WILL CERTAINLY MOVE S AND E OF THE AREA BY MIDNIGHT...BUT WILL
LEAVE SLGHT CHC/CHC POPS AHEAD OF FRONTAL POS THROUGH TONIGHT WITH
HIGHEST POPS IN E ZONES. WILL SIDE WITH ETA GRIDS AND MOVE CHC
FOR PCP OUT OF THE AREA BY 12Z MONDAY WITH CLOUDS DECREASING
DURING THE MORNING. MUCH DRIER AIR WITH BLYR DEWPOINTS IN THE
40S WILL PUSH SOUTHWARD INTO THE AREA LATE MONDAY AND MONDAY
NIGHT WITH SUNNY SKY EXPECTED TO LET TEMPS WARM NICELY ON TUE.
FAIR WEATHER EXPECTED INTO LATE WEEK WITH CHC FOR THUNDERSTORMS
AHEAD OF FRONT ON FRI CONDITIONAL ON RETURN OF SIG LOW LEVEL
MOISTURE...BUT IT IS STILL MAY SO CERTAINLY CLIMATOLOGY FAVORS
IT.

GENERALLY FAVORED COOLER MAV TEMPS ESP FOR MONDAY MAXES AND
MONDAY NIGHT MINS.

FCSTID = 13
TUL   57  75  50  78 /  20   0   0   0
FSM   60  75  52  78 /  60  10   0   0
MLC   60  75  52  78 /  50  10   0   0
BVO   53  75  48  78 /  20   0   0   0
FYV   57  72  45  75 /  60  10   0   0
BYV   57  72  45  75 /  60  10   0   0
MIO   57  72  45  75 /  60  10   0   0
MKO   60  75  52  78 /  50  10   0   0
F10   57  75  50  78 /  20   0   0   0
HHW   62  78  55  79 /  60  W10   0   0

.TSA...
AR...NONE.
OK...NONE.

ARZ001-002-010-011-019-020-029-OKZ049-053>076-071100-

EASTERN OKLAHOMA/NORTHWEST ARKANSAS HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TULSA OK
100 PM CDT SUN MAY 6 2001

...A FEW SEVERE THUNDERSTORMS EXPECTED LATE THIS AFTERNOON ACROSS
EASTERN OKLAHOMA AND THIS EVENING ACROSS NORTHWEST ARKANSAS...

EARLY THIS AFTERNOON...A SURFACE DRYLINE WAS LOCATED ACROSS WESTERN
OKLAHOMA. MEANWHILE...AN UPPER LEVEL SHORTWAVE WAS CROSSING THE
OKLAHOMA PANHANDLE...EXTENDING FROM NEAR WOODWARD TO WICHITA FALLS
TEXAS. THE APPROACHING UPPER LEVEL STORM SYSTEM WILL INTERACT WITH
THE SURFACE BOUNDARY THIS AFTERNOON...GENERATING ANOTHER ROUND OF
SHOWERS AND THUNDERSTORMS. INCREASING INSTABILITY AT THE SURFACE AND
STRONG UPPER LEVEL FORCING INDICATE SOME OF THE STORMS MAY BECOME
SEVERE ACROSS EASTERN OKLAHOMA THIS AFTERNOON...AND NORTHWEST
ARKANSAS TONIGHT.

.SPOTTER ACTIVATION...
ACTIVATION OF STORM SPOTTERS WILL MORE THAN LIKELY BE REQUIRED LATER
TODAY. LAW ENFORCEMENT AGENCIES...EMERGENCY MANAGEMENT OFFICIALS AND
STORM SPOTTER GROUPS SHOULD CONTINUE TO MONITOR FOR LATER UPDATES.

.DISCUSSION...
MORNING UPPER AIR ANALYSIS REVEALED SEVERAL SHORTWAVES ASSOCIATED
WITH THE MAIN UPPER LEVEL LOW PRESSURE...WHICH IS CURRENTLY LOCATED
ACROSS SOUTH DAKOTA. ONE OF THESE SHORTWAVES WILL MOVE INTO EASTERN
OKLAHOMA BY 4 PM THIS AFTERNOON...AND BY 7PM ACROSS NORTHWEST
ARKANSAS. SURFACE DEWPOINTS ARE ONLY IN THE UPPER 50S ACROSS
NORTHEAST OKLAHOMA...BUT MOISTURE CONVERGENCE WILL INCREASE THIS
AFTERNOON. A SURGE OF MOIST AIR...WITH DEWPOINTS RANGING FROM THE
MID 60S TO NEAR 70 DEGREES...WILL MOVE EAST TODAY AHEAD OF THE
DRYLINE. AS OF EARLY AFTERNOON...LAPS DATA AND SURFACE OBSERVATIONS
SHOWED A PLUME OF 65-70 DEGREE DEWPOINT AIR FROM ENID TO OKLAHOMA
CITY TO ARDMORE.

THE 12Z NORMAN SOUNDING SHOWED A STRONG CAP...WHICH WILL INHIBIT
THUNDERSTORM DEVELOPMENT UNTIL THE SHORTWAVE GETS CLOSER. HOWEVER
CONVECTIVE TEMPERATURES ARE ONLY IN THE MIDDLE TO UPPER 70S...AND SO
THE CAP SHOULD BE OVERCOME WITH DAYTIME HEATING. STEEP LAPSE RATES
WILL MAKE THE ATMOSPHERE EXTREMELY UNSTABLE BY AFTERNOON. THE LATEST
VISIBLE SATELLITE IMAGERY SHOWED MOSTLY SUNNY SKIES ACROSS WESTERN
OKLAHOMA...AND PARTLY TO MOSTLY CLOUDY SKIES ACROSS THE REST OF THE
STATE. SURFACE CAPES IN SOUTHWEST OKLAHOMA WERE APPROACHING 2500
J/KG...AND LIFTED INDEX VALUES WERE NEAR -8. THIS UNSTABLE AIR MASS
WILL BE ADVECTED EAST BY LATE THIS AFTERNOON...WITH THE APPROACH OF
THE SHORTWAVE AND SURFACE BOUNDARY.

CONVECTIVE INITIATION THIS AFTERNOON WILL OCCUR JUST EAST OF THE
DRYLINE...LIKELY ALONG AND EAST OF THE INTERSTATE 35 CORRIDOR. ONCE
STORMS ARE ABLE TO DEVELOP...THEY WILL RAPIDLY BECOME SEVERE.

UPPER WIND PROFILES SHOW STRONG VEERING WITH HEIGHT...WHICH
INDICATES SUPERCELLS ARE LIKELY. UPPER FLOW IS NOT AS STRONG AS IT
COULD BE...BUT THE DIRECTIONAL SHEAR IS SUFFICIENT FOR
SUPERCELLS...AND POSSIBLY TORNADO DEVELOPMENT BY LATE THIS
AFTERNOON. THE MAIN THREAT FROM STORMS WILL BE FROM LARGE
HAIL...WITH A SECONDARY THREAT FROM TORNADOES...PARTICULARLY SOUTH
AND EAST OF A JAY TO MCALESTER LINE...WHERE WIND FIELDS WILL BE MOST
VEERED.

THREAT TABLE
VALID THROUGH 1200 UTC MONDAY

THREAT AREA 1...EASTERN OKLAHOMA AND NORTHWEST ARKANSAS
THUNDERSTORM PROBABILITY...100
SEVERE PROBABILITY IF STORMS OCCUR...80
SIGNIFICANT SEVERE PROBABILITY IF STORMS OCCUR...50

THREAT AREAS DEFINE THE GREATEST RISK. PROBABILITIES ARE IN PERCENT.
SIGNIFICANT SEVERE IS DEFINED AS F1 OR GREATER WIND/TORNADO DAMAGE
AND/OR GOLFBALL SIZE HAIL OR LARGER.

A GERAPHICAL VERSION OF THIS OUTLOOK CAN BE FOUND AT:
WWW.SRH.NOAA.GOV/TULSA

SJT