Severe Thunderstorm Warning 276, NWS Tulsa, OK

EASTERN OKLAHOMA/NORTHWEST ARKANSAS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TULSA OK
515 AM CDT FRI MAY 21 1999

PROBLEM(S) OF THE DAY:
POPS
TEMPERATURES

THIS IS MY FIRST SHIFT ON THE PUBLIC DESK SINCE EARLY APRIL...
SO PAST CONTINUITY MAY BE LACKING.

EARLY MORNING SURFACE ANALYSIS SHOWS COLD FRONT MAKING STEADY
PROGRESS TO THE SOUTH. TSRA SHOULD TAPER OFF LATE IN THE MORNING
AS MID-LEVEL SUPPORT MOVES SOUTHEAST. FASHIONED POPS IN THE FIRST
PERIOD BY JUDGING WHERE PRECIP WILL BE BY 7 AM...THE FIRST HOUR OF
POP VERIFICATION FOR THE FIRST PERIOD. THIS WILL ALSO HOPEFULLY
PREVENT AN UPDATE BEFORE 8 AM.

FRONT WILL THEN HANG UP NEAR THE RED RIVER TONIGHT AND SATURDAY...
BRINGING A STRONGER COOL-DOWN TO THE NRN ZNS THAN THE SOUTH FOR
TONIGHT. COULD BE A GOOD RADIATIONAL COOLING NIGHT IN THE NRN ZNS.
ON SAT...SOUTHWEST WINDS OFF OF THE SURFACE WILL HELP BUILD A CAP
THAT WILL INHIBIT CONVECTION...DESPITE MODERATE INSTABILITIES. WILL
ONLY LEAVE IN A 20 POP FOR TONIGHT AND SAT IN THE FAR SRN ZNS DUE TO
THE PROXIMITY OF THE DISSIPATING FRONT. BY SAT AFTN...SOUTHERLY
FLOW IS RETURNING AND SO ARE INCREASING DEWPOINTS IN ADVANCE OF THE
NEXT STRONGER FRONT WHICH WILL APPROACH THE AREA LATE SAT NGT. THE
CAP MAY LIMIT THE SOUTHWARD EXTENT OF CONVECTIVE DEVELOPMENT ALONG
THE FRONT...BUT IT LOOKS LIKE MID-LEVEL COOLING IN ASSOCIATION WITH
A DEVELOPING MID-LEVEL LOW OVER IA/MN WILL BE ENOUGH TO BREAK THE CAP
IN THE NRN ZNS LATE SAT NGT. STRONGER MID-LEVEL WINDS WILL ALSO BE
CONFINED TO THE FAR NRN ZNS...KEEPING THE THREAT FOR ORGANIZED
ACTIVITY MOSTLY CONFINED TO THE NRN ZNS. A FAVORABLE THICKNESS
DIFLUENCE PATTERN SUGGESTS ONE OR MORE MCS'S COULD FORM ALONG THE
FRONT AND DIVE SOUTHEAST DURING THE LATE NIGHT/EARLY MORNING HOURS.

THE FRONT WILL CLEAR THE AREA ON SUN AFTN AND MOVE ALL THE WAY INTO
THE GULF OF MEXICO. THIS WILL LEAVE A PLEASANTLY COOL AND DRY PACIFIC
AIR MASS ENTRENCHED ACROSS THE AREA THROUGH MID-WEEK.

TEMPERATURES IN THIS FORECAST PACKAGE ARE LARGELY BASED ON AVERAGE
MODEL PERFORMANCE OVER THE PAST 30 DAYS WITH EXTRA WEIGHT GIVEN TO
MODEL TRENDS THIS PAST WEEK. IN GENERAL...THE AVN MOS HAS
OUTPERFORMED THE NGM MOS...WITH THE NGM MOS ESPECIALLY BEING TOO
WARM AT NIGHT.

FCSTID = 22
TUL   80  59  84  62 /  30   5   5  40
FSM   82  61  87  63 /  40  10  10  30
MLC   83  59  85  65 /  50  10  20  30
BVO   81  56  85  59 /  20   5   5  50
FYV   79  54  82  60 /  70   5   5  50
IDB   88  60  86  64 /  30  20  20  20
BYV   79  53  82  59 /  70   5   5  50
MIO   80  54  83  60 /  70   5   5  50
MKO   81  59  85  62 /  30   5   5  40
F10   82  59  85  62 /  30   5   5  40
HHW   87  60  86  64 /  30  20  20  20

.TUL...
AR...NONE.
OK...NONE.

--------------------
EXPERIMENTAL OUTPUT:

HAZARDOUS WEATHER EXPECTED NEXT 24 HOURS: SLIGHT CHANCE SEVERE
THUNDERSTORMS
NGM CONFIDENCE:  7 ON A SCALE OF 0 TO 10
ETA CONFIDENCE:  7 ON A SCALE OF 0 TO 10
AVN CONFIDENCE:  7 ON A SCALE OF 0 TO 10
FCST CONFIDENCE: 8 ON A SCALE OF 0 TO 10

ARZ001-002-010-011-019-020-029-OKZ049-053>076-221100-

EASTERN OKLAHOMA/NORTHWEST ARKANSAS HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TULSA OK
600 AM CDT FRI MAY 21 1999

ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE THROUGH 10 AM THIS
MORNING SOUTH OF A LINE FROM OKMULGEE TO MUSKOGEE TO FORT SMITH.

ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE LATE THIS AFTERNOON AND
THIS EVENING SOUTHEAST OF A LINE FROM BENTONVILLE ARKANSAS TO
MCALESTER OKLAHOMA.

.SYNOPSIS...
A WEAK COLD FRONT EXTENDED FROM NEAR MANHATTAN KANSAS TO ALTUS
OKLAHOMA EARLY THIS MORNING. THIS FRONT WILL SAG SLOWLY SOUTHEAST
TODAY AND WILL MOVE THROUGH NORTHEAST OKLAHOMA TODAY BEFORE STALLING
FROM WEST CENTRAL ARKANSAS INTO SOUTHEAST OKLAHOMA TONIGHT.

.DISCUSSION...
THUNDERSTORMS ONGOING EARLY THIS MORNING ARE EXPECTED TO GENERALLY
REMAIN BELOW SEVERE LIMITS. HOWEVER...ONE OR TWO ISOLATED STORMS MAY
BECOME MARGINALLY SEVERE AND PRODUCE DIME SIZE HAIL OR 60 MILE AN
HOUR WINDS SOUTH OF AN OKMULGEE TO MUSKOGEE TO FORT SMITH LINE
THROUGH 10 AM.

THE AIRMASS WILL BECOME MODERATELY UNSTABLE AHEAD OF THE COLD FRONT
THIS AFTERNOON. ALTHOUGH UPPER LEVEL SUPPORT WILL BE LACKING AND LOW
LEVEL CONVERGENCE ALONG THE COLD FRONT WILL BE RELATIVELY
WEAK...THERE MAY BE JUST ENOUGH CONVERGENCE FOR ISOLATED
THUNDERSTORMS TO DEVELOP LATE THIS AFTERNOON SOUTHEAST OF A
BENTONVILLE TO MCALESTER LINE. IF STORMS DO DEVELOP...THE AMOUNT OF
INSTABILITY PRESENT SUGGESTS THAT THEY WILL HAVE THE POTENTIAL TO
BECOME SEVERE AND PRODUCE LARGE HAIL AND DAMAGING WINDS.

ALTHOUGH WIND PROFILES ARE NOT OVERLY SUPPORTIVE OF SUPERCELL
STORMS...SOME POTENTIAL DOES EXIST FOR DEVIANT STORM MOTIONS TO THE
SOUTH. IF A STORM CAN MOVE DUE SOUTH OR EVEN SOUTH SOUTHWEST...IT
MAY TAKE ON SUPERCELLULAR CHARACTERISTICS AND A BRIEF TORNADO MAY
THEN BE POSSIBLE.

THUNDERSTORMS ARE EXPECTED TO DISSIPATE BY LATE EVENING AS COOLING
TEMPERATURES STABILIZE THE AIRMASS.

.EMERGENCY MANAGEMENT AGENCY AND SPOTTER ACTIVATION...
EMERGENCY MANAGEMENT AGENCIES AND SPOTTER ORGANIZATIONS ACROSS
SOUTHEAST OKLAHOMA AND NORTHWEST ARKANSAS SHOULD BE PREPARED FOR
POSSIBLE ACTIVATION EARLY THIS MORNING AND AGAIN LATE THIS AFTERNOON
AND EVENING.

AN UPDATED HAZARDOUS WEATHER OUTLOOK WILL BE ISSUED AROUDN 1 PM THIS
AFTERNOON.

ARZ001-002-010-011-019-020-029-OKZ049-053>076-221100-

EASTERN OKLAHOMA/NORTHWEST ARKANSAS HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TULSA OK
600 AM CDT FRI MAY 21 1999

ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE THROUGH 10 AM THIS
MORNING SOUTH OF A LINE FROM OKMULGEE TO MUSKOGEE TO FORT SMITH.

ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE LATE THIS AFTERNOON AND
THIS EVENING SOUTHEAST OF A LINE FROM BENTONVILLE ARKANSAS TO
MCALESTER OKLAHOMA.

.SYNOPSIS...
A WEAK COLD FRONT EXTENDED FROM NEAR MANHATTAN KANSAS TO ALTUS
OKLAHOMA EARLY THIS MORNING. THIS FRONT WILL SAG SLOWLY SOUTHEAST
TODAY AND WILL MOVE THROUGH NORTHEAST OKLAHOMA TODAY BEFORE STALLING
FROM WEST CENTRAL ARKANSAS INTO SOUTHEAST OKLAHOMA TONIGHT.

.DISCUSSION...
THUNDERSTORMS ONGOING EARLY THIS MORNING ARE EXPECTED TO GENERALLY
REMAIN BELOW SEVERE LIMITS. HOWEVER...ONE OR TWO ISOLATED STORMS MAY
BECOME MARGINALLY SEVERE AND PRODUCE DIME SIZE HAIL OR 60 MILE AN
HOUR WINDS SOUTH OF AN OKMULGEE TO MUSKOGEE TO FORT SMITH LINE
THROUGH 10 AM.

THE AIRMASS WILL BECOME MODERATELY UNSTABLE AHEAD OF THE COLD FRONT
THIS AFTERNOON. ALTHOUGH UPPER LEVEL SUPPORT WILL BE LACKING AND LOW
LEVEL CONVERGENCE ALONG THE COLD FRONT WILL BE RELATIVELY
WEAK...THERE MAY BE JUST ENOUGH CONVERGENCE FOR ISOLATED
THUNDERSTORMS TO DEVELOP LATE THIS AFTERNOON SOUTHEAST OF A
BENTONVILLE TO MCALESTER LINE. IF STORMS DO DEVELOP...THE AMOUNT OF
INSTABILITY PRESENT SUGGESTS THAT THEY WILL HAVE THE POTENTIAL TO
BECOME SEVERE AND PRODUCE LARGE HAIL AND DAMAGING WINDS.

ALTHOUGH WIND PROFILES ARE NOT OVERLY SUPPORTIVE OF SUPERCELL
STORMS...SOME POTENTIAL DOES EXIST FOR DEVIANT STORM MOTIONS TO THE
SOUTH. IF A STORM CAN MOVE DUE SOUTH OR EVEN SOUTH SOUTHWEST...IT
MAY TAKE ON SUPERCELLULAR CHARACTERISTICS AND A BRIEF TORNADO MAY
THEN BE POSSIBLE.

THUNDERSTORMS ARE EXPECTED TO DISSIPATE BY LATE EVENING AS COOLING
TEMPERATURES STABILIZE THE AIRMASS.

.EMERGENCY MANAGEMENT AGENCY AND SPOTTER ACTIVATION...
EMERGENCY MANAGEMENT AGENCIES AND SPOTTER ORGANIZATIONS ACROSS
SOUTHEAST OKLAHOMA AND NORTHWEST ARKANSAS SHOULD BE PREPARED FOR
POSSIBLE ACTIVATION EARLY THIS MORNING AND AGAIN LATE THIS AFTERNOON
AND EVENING.

AN UPDATED HAZARDOUS WEATHER OUTLOOK WILL BE ISSUED AROUDN 1 PM THIS
AFTERNOON.