Tornadoes and Flash Flooding in Oklahoma, May 20 to 21, 2001

EASTERN OKLAHOMA/NORTHWEST ARKANSAS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TULSA OK
317 PM CDT SUN MAY 20 2001

TORNADO WATCH JUST ISSUED FOR A LARGE PART OF EASTERN OKLAHOMA.
EXPECT SCATTERED SUPERCELL THUNDERSTORMS TO DEVELOP ALONG NORTHWARD
MOVING WARM FRONT CURRENTLY ANALYZED ACROSS SOUTHEAST OKLAHOMA.
DEGREE OF INSTABILITY AND STRENGTH OF WIND FIELDS SUGGEST HIGH
POTENTIAL FOR ROTATING STORMS...WITH A FEW TORNADOES POSSIBLE
ESPECIALLY FROM ANY RIGHT-MOVING STORMS. EXPECT ACTIVITY TO EVOLVE
INTO ANOTHER COMPLEX THIS EVENING AND MOVE EAST ACROSS AREA
OVERNIGHT. WILL GO WITH LIKELY POPS ALL ZONES...WITH FROPA LATE
TONIGHT BRINGING A RAPID END TO SIGNIFICANT CONVECTION.

WINDY AND COOLER WILL BE THE MAIN WEATHER STORY ON MONDAY...WITH A
FEW SHOWERS POSSIBLE AS COLD AIR ALOFT SWINGS ACROSS AREA. MAY SEE
FALLING OR STEADY AFTERNOON TEMPERATURES IN MANY ZONES.

SKIES SHOULD CLEAR MONDAY NIGHT...WITH VERY COOL NIGHT EXPECTED.
NEAR RECORD LOW TEMPERATURES POSSIBLE IN SOME AREAS...ESPECIALLY IF
WINDS DIE OFF MORE THAN EXPECTED.

MOSTLY CLEAR AND DRY WEATHER EXPECTED ON TUESDAY AS TEMPERATURES
REBOUND INTO THE 60S AND 70S.

IN EXTENDED...DRY WEATHER WITH NEAR OR SLIGHTLY BELOW NORMAL
TEMPERATURES EXPECTED FOR MOST OF THE WEEK AS LARGE CUTOFF DEVELOPS
OVER EASTERN U.S. UPPER RIDGING DEVELOPS BY LATE IN THE WEEK AND
NEXT WEEKEND...WITH WARMING TEMPERATURES AND CONTINUED DRY WEATHER
EXPECTED.

FCSTID = 9
TUL   56  62  44  68 /  60  40  10   0
FSM   63  67  45  72 /  70  50  10  10
MLC   60  66  45  72 /  60  40  10  10
BVO   54  60  43  68 /  60  30  10   0
FYV   59  62  41  64 /  70  50  10  10
BYV   58  61  40  63 /  70  50  10  10
MIO   57  61  42  66 /  60  40  10   0
MKO   60  65  45  70 /  60  40  10  10
F10   57  63  44  69 /  60  40  10   0
HHW   67  70  48  74 /  60  30  10   0

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

ARZ001-002-010-011-019-020-029-OKZ049-053>076-211100-

EASTERN OKLAHOMA/NORTHWEST ARKANSAS HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TULSA OK
105 PM CDT SUN MAY 20 2001

...NUMEROUS SEVERE THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND
EVENING ACROSS EASTERN OKLAHOMA AND NORTHWEST ARKANSAS...

AT MIDDAY...A LOW PRESSURE TROUGH EXTENDED SOUTH FROM A LOW PRESSURE
SYSTEM LOCATED IN SOUTH CENTRAL NEBRASKA INTO THE TEXAS PANHANDLE.
AN OUTFLOW BOUNDARY FROM THIS MORNINGS THUNDERSTORMS WAS LOCATED
ACROSS SOUTHEAST OKLAHOMA.  SOUTHERLY WINDS WERE INCREASING ACROSS
THE AREA AHEAD OF THE TROUGH WHICH WILL HELP TO MOVE THE OUTFLOW
BOUNDARY NORTHWARD THIS AFTERNOON.

IN ADDITION...AN UPPER LEVEL DISTURBANCE CURRENTLY LOCATED IN
NORTHWEST OKLAHOMA WILL CONTINUE TO MOVE EASTWARD INTO ARKANSAS BY
TONIGHT.  THIS UPPER SYSTEM IN CONJUNCTION WITH FAVORABLE UPPER
LEVEL WINDS WILL COMBINE TO PRODUCE THUNDERSTORMS ACROSS NORTHEAST
OKLAHOMA AND NORTHWEST ARKANSAS ALONG THE OUTFLOW BOUNDARY THIS
AFTERNOON.  THE THUNDERSTORMS SHOULD THEN EVOLVE INTO A LINE AND
MOVE EAST INTO ARKANSAS BY TONIGHT.

.SPOTTER ACTIVATION...
SPOTTER ACTIVATION WILL LIKELY BE REQUIRED BEFORE 4 PM ACROSS
PORTIONS OF EASTERN OKLAHOMA AND NORTHWEST ARKANSAS.

.DISCUSSION...
OUTFLOW BOUNDARY FROM THIS MORNINGS CONVECTIVE COMPLEX IS CURRENTLY
POSITIONED ACROSS SOUTHEAST OKLAHOMA FROM NEAR IDABEL TO HUGO ON
INTO SOUTH CENTRAL OKLAHOMA.  DEWPOINTS SOUTH OF THE BOUNDARY ARE IN
THE MID 70S WITH UPPER 60S TO NEAR 70 DEGREE DEWPOINTS NORTH OF THE
BOUNDARY.  LATEST FORECAST CAPE VALUES OF 3000 TO 4000 J/KG WILL BE
IN PLACE ACROSS MUCH OF THE AREA THIS AFTERNOON INTO THE EVENING
HOURS.  SOUTHERLY WINDS ARE EXPECTED TO HELP MOVE THE OUTFLOW
BOUNDARY FURTHER NORTH THIS AFTERNOON INTO EAST CENTRAL OKLAHOMA
AROUND 4 PM.  THIS BOUNDARY SHOULD PROVIDE THE FOCUS FOR
THUNDERSTORM INITIATION.  LARGE HAIL OF GOLFBALL SIZE OR LARGER WILL
BE POSSIBLE WITH THESE STORMS.  ISOLATED TORNADOES WILL ALSO BE A
THREAT MAINLY ALONG THE OUTFLOW BOUNDARY THIS AFTERNOON AND EARLY
EVENING BEFORE THE SYSTEM EVOLVES INTO LINE AND MOVES EAST INTO
ARKANSAS.

THREAT TABLE
VALID THROUGH 1200 UTC MONDAY

AREA 1...MUCH OF EASTERN OKLAHOMA AND NORTHWEST ARKANSAS
THUNDERSTORM PROBABILITY...95
SEVERE PROBABILITY IF STORMS OCCUR...90
SIGNIFICANT SEVERE PROBABILITY IF STORMS OCCUR...40

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.

RELATED GRAPHICAL INFORMATION CAN BE FOUND AT: WWW.SRH.NOAA.GOV/TULSA

AN UPDATED HAZARDOUS WEATHER OUTLOOK WILL BE ISSUED AROUND 1 PM
TODAY.