Severe Thunderstorm Warning 78, NWS Tulsa, OK

EASTERN OKLAHOMA/NORTHWEST ARKANSAS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TULSA OK
922 PM CDT WED APR 19 2000

CAPPING INVERSION AND WEAK CONVERGENCE ALONG DRYLINE HAS KEPT
BOUNDARY-LAYER BASED CONVECTION FROM DEVELOPING ACROSS THE FORECAST
AREA SO FAR THIS EVENING. SURFACE OBSERVATIONS AND SATELLITE IMAGERY
SHOW THE DRYLINE EXTENDING FROM SOUTHEAST KANSAS ACROSS THE
NORTHWEST CORNER OF OSAGE COUNTY TO JUST NORTHWEST OF KOKC.  SURFACE
COLD FRONT WAS SURGING RAPIDLY SOUTHEAST ACROSS CENTRAL KANSAS AND
NORTHWEST OKLAHOMA.

EVENING UPPER AIR ANALYSIS INDICATED AN UPPER LEVEL SPEED MAX MOVING
NORTHEAST ACROSS TEXAS PANHANDLE. RAPID DEVELOPMENT OF CLOUDS IN
NORTHWEST OKLAHOMA SUGGESTS THAT LIFT ASSOCIATED WITH THE SPEED MAX
WAS SPREADING EAST.

STILL EXPECT AT LEAST SCATTERED SEVERE STORMS TO AFFECT THE FORECAST
AREA TONIGHT. CURRENT INDICATIONS ARE THAT CONVECTION MAY INITIALLY
FIRE TO THE WEST BETWEEN 10 AND 11 PM AS COLD FRONT CATCHES UP TO
DRYLINE AND STRONG INSTABILITY IS RELEASED. THE UPPER SPEED MAX WILL
PROVIDE THE LIFT/DYNAMICS TO KEEP THE STORMS GOING WELL INTO THE
NIGHT AS CONVECTION MOVES ACROSS THE AREA.

THERE ARE STILL SOME UNCERTAINTIES REGARDING COVERAGE OF STORMS
TONIGHT...SO I PREFER NOT TO ADJUST FIRST PERIOD OF FORECAST AT THIS
TIME. HOWEVER...IF STORMS DO INDEED FIRE ALONG THE COLD FRONT AS
EXPECTED...WILL THEN ISSUE AN UPDATE TO RAISE POPS TO CATEGORICAL IN
SOME AREAS WITH POTENTIAL FOR RAPIDLY MOVING SQUALL LINE.

FCSTID = 9

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

ARZ001-002-010-011-019-020-029-OKZ049-053>076-201200-

EASTERN OKLAHOMA/NORTHWEST ARKANSAS HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TULSA OK
945 PM CDT WED APR 19 2000

...A FEW SEVERE THUNDERSTORMS ARE EXPECTED LATE TONIGHT THROUGH
EARLY THURSDAY MORNING ACROSS EASTERN OKLAHOMA AND NORTHWEST
ARKANSAS...

.SYNOPSIS...
SURFACE LOW PRESSURE WAS LOCATED OVER NORTHEAST NEBRASKA THIS
EVENING. THE DRYLINE EXTENDED SOUTH FROM THE LOW THROUGH EASTERN
KANSAS INTO CENTRAL OKLAHOMA. THE DRYLINE WAS RETREATING TO THE
WEST...AS A STRONG COLD FRONT WAS RAPIDLY ADVANCING SOUTHEAST ACROSS
NORTHWEST OKLAHOMA. THE INTERSECTION OF THE COLD FRONT AND THE
DRYLINE WILL RESULT IN SCATTERED SEVERE THUNDERSTORMS LATE THIS
EVENING ACROSS NORTHEAST OKLAHOMA AND NORTHWEST ARKANSAS.

.PRIMARY HAZARD...
SEVERE THUNDERSTORMS ARE STILL EXPECTED TO DEVELOP ACROSS EASTERN
OKLAHOMA AND NORTHWEST ARKANSAS LATE TONIGHT. THE MAIN THREAT FROM
THESE STORMS WILL BE LARGE HAIL...AND DAMAGING STRAIGHT LINE WINDS.
IN ADDITION...ISOLATED TORNADOES MAY ALSO DEVELOP DUE TO SUFFICIENT
SHEAR.

.DISCUSSION...
VERY WARM AIR ALOFT KEPT THUNDERSTORMS FROM FIRING UP MOST OF THE DAY
ACROSS OKLAHOMA AND ARKANSAS. THE CAP DID BREAK IN SOME LOCATIONS
THIS AFTERNOON AND EARLY EVENING...MAINLY ACROSS EASTERN KANSAS AND
WESTERN MISSOURI. SOME ELEVATED CONVECTION ALSO DEVELOPED ACROSS
NORTHWEST ARKANSAS. HOWEVER EVENING SOUNDINGS AT 7 PM REVEALED THE
ENVIRONMENT WAS TOO WARM AT MID LEVELS TO SUPPORT SURFACE BASED
THUNDERSTORMS...DESPITE INCREASING INSTABILITY.

STORMS ARE EXPECTED TO DEVELOP LATE TONIGHT ACROSS NORTH CENTRAL
OKLAHOMA...AS THE RETREATING DRYLINE MERGES WITH THE ADVANCING COLD
FRONT. THIS WILL PROVIDE THE LIFT NECESSARY TO INITIATE
THUNDERSTORMS. GIVEN THE UNSTABLE ENVIRONMENT THESE STORMS WILL MOVE
INTO...IT IS LIKELY THE STORMS WILL QUICKLY BECOME SEVERE.

.SPOTTER ACTIVATION...
SPOTTERS ACROSS EASTERN OKLAHOMA AND NORTHWEST ARKANSAS SHOULD BE
PREPARED FOR ACTIVATION TONIGHT.  THE MOST LIKELY TIME FOR
ACTIVATION WILL BE BETWEEN 11 PM AND 1 AM IN EASTERN OKLAHOMA AND 2
AM AND 5 AM OVER NORTHWEST ARKAENSAS.