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471
ABUS34 KTUL 181913
PNSTUL
PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE TULSA OK
113 PM CST MON MAR 18 1994
...ROUTINE THUNDERSTORM OUTLOOKS BEGAN TODAY...
THE DAILY ISSUANCE OF THE EAST OKLAHOMA / NORTHWEST ARKANSAS
THUNDERSTORM OUTLOOK BEGAN TODAY. THESE OUTLOOKS WILL BE SENT AT
600 AM AND 100 PM EACH DAY THROUGH MID JUNE USING THE PRODUCT
IDENTIFIER OKCSPSTUL. THE OUTLOOKS WILL COVER OKLAHOMA ZONES 54
THROUGH 77 AND ARKANSAS ZONES 1...2...10...11...19...AND 29.
THE PURPOSE OF THE THUNDERSTORM OUTLOOK IS TO PROVIDE DETAILED
INFORMATION ON THE POTENTIAL FOR THUNDERSTORMS...WITH EMPHASIS ON
THE POSSIBILITIES OF SEVERE WEATHER. THE OUTLOOKS WILL BE VALID
FROM THE ISSUANCE TIME THROUGH 600 AM CST OR 700 AM CDT THE NEXT
MORNING.
IN THE OUTLOOKS THE STORM POTENTIAL IS CATEGORIZED USING BOTH
COVERAGE AND PROBABILITY DESCRIPTORS. THIS REPLACES THE RISK
CATEGORY WHICH ATTEMPTED TO COMBINE BOTH THE COVERAGE AND
PROBABILITY INTO ONE TERM...AND WAS OFTEN MISINTERPRETED.
COVERAGE TERMS USED WILL BE ISOLATED...A FEW AND NUMEROUS.
PROBABILITY TERMS USED WILL BE EXPECTED AND POSSIBLE. FOR
EXAMPLE...WHEN A FORECASTER BELIEVES THAT A NUMBER OF SEVERE STORMS
COULD OCCUR THE PHRASE...A FEW SEVERE THUNDERSTORMS ARE
POSSIBLE...WILL BE USED.
THESE OUTLOOKS ARE INTENDED FOR USE BY A WIDE VARIETY OF
PEOPLE...AND THEREFORE CONTAIN A SOMEWHAT DETAILED METEOROLOGICAL
EXPLANATION OF THE SITUATION. TO HELP INTERPRET SOME OF THE
INFORMATION...A GLOSSARY HAS BEEN PUT TOGETHER THAT DEFINES THE
MORE COMMONLY USED TERMS. THIS GLOSSARY SHOULD BE SAVED AND
REFERENCED AS NECESSARY.
...GLOSSARY OF TERMS USED IN THE THUNDERSTORM OUTLOOKS...
CAP............A LAYER OF WARM AIR SEVERAL THOUSAND FEET ABOVE
THE GROUND THAT EFFECTIVELY KEEPS A LID ON
UNSTABLE AIR AND PREVENTS THUNDERSTORMS FROM
FORMING. ON CERTAIN DAYS ALL CONDITIONS IMPORTANT
TO SEVERE THUNDERSTORM DEVELOPMENT CAN BE FAVORABLE
...BUT THE CAP PREVENTS STORM DEVELOPMENT.
COLD FRONT.....A TRANSITION ZONE THAT MARKS WHERE COLDER AIR
IS MOVING INTO WARMER AIR. THUNDERSTORMS CAN FORM
ALONG A COLD FRONT WHEN THE ATMOSPHERE IS MOIST AND
UNSTABLE.
CONVERGENCE....A WIND PATTERN THAT RESULTS IN AIR BEING FORCED INTO
THE SAME GENERAL AREA. CONVERGENCE OCCURS ALONG
FRONTS AND IS THE MECHANISM THAT PILES THE AIR UP
AND FORCES IT TO RISE.
DEW POINT......A MEASURE OF THE AMOUNT OF MOISTURE IN THE AIR. IT
IS THE TEMPERATURE TO WHICH THE AIR MUST COOL TO
REACH A HUMIDITY OF 100 PERCENT. THE DEW POINT CAN
EQUAL BUT NEVER BE MORE THAN THE TEMPERATURE. IN
THE COOLER TIMES OF YEAR A GOOD RULE OF THUMB IS
THAT THE DEW POINT AT THE GROUND SHOULD BE 55
DEGREES OR HIGHER FOR SEVERE THUNDERSTORMS TO OCCUR.
DURING THE WARMER TIMES OF YEAR A DEW POINT OF 65
DEGREES OR BETTER IS IMPORTANT. A DEW POINT GREATER
THAN 60 IS HIGH IN THE WINTER AND A DEW POINT
GREATER THAN 70 IS HIGH IN THE SUMMER. THE
DEW POINT RARELY EXCEEDS 80 DEGREES IN OKLAHOMA.
DIVERGENCE...A WIND PATTERN THAT RESULTS IN AIR BEING FORCED AWAY
FROM THE SAM GENERAL AREA. DIVERGENCE IN THE UPPER
LEVELS OF THE ATMOSPHERE VENTILATES THE ATMOSPHERE
LIKE A CHIMNEY AND HELPS LOW-LEVEL AIR TO RISE.
DRY LINE.......A TRANSITION ZONE THAT MARKS THE DIVISION BETWEEN
AIR OF HIGH HUMIDITY AND VERY LOW HUMIDITY.
BECAUSE DRY AIR IS MORE DENSE THAN HUMID AIR
IT LIFTS THE HUMID AIR.
THUNDERSTORMS CAN FORM ALONG A DRY LINE WHEN THE
ATMOSPHERE IS UNSTABLE.
HIGH PRESSURE
CENTER.........A REGION OF HIGHER BAROMETRIC PRESSURE WHERE THE
AIR SPIRALS OUT AWAY FROM THE CENTER. HIGH PRESSURE
CENTERS ARE TYPICALLY ASSOCIATED WITH FAIR WEATHER.
INSTABILITY....A MEASURE OF THE TEMPERATURE DIFFERENCE BETWEEN
AIR ALOFT AND AIR IN THE LOWER LEVELS OF THE
ATMOSPHERE. THE COLDER THE AIR IS ALOFT AND
THE WARMER IT IS NEAR THE GROUND...THE MORE
UNSTABLE THE ATMOSPHERE. THE GREATER THE
INSTABILITY...THE GREATER THE THREAT FOR
THUNDERSTORMS. THUNDERSTORMS CAN OCCUR EVEN ON
COOL DAYS WHEN THE AIR ALOFT GETS VERY COLD.
JET STREAM.....A STREAM OF FAST MOVING AIR IN THE UPPER LEVELS
OF THE ATMOSPHERE. THIS STREAM OF AIR STEERS STORMS
SYSTEMS ACROSS COUNTY. THUNDERSTORMS THAT FORM
IN THE VICINITY OF A JET STREAM CAN ORGANIZE
INTO LONG LIVED SEVERE WEATHER PRODUCERS.
LOW PRESSURE
CENTER.........A REGION OF LOWER BAROMETRIC PRESSURE WHERE THE
AIR SPIRALS IN TOWARD THE CENTER IN A
COUNTER-CLOCKWISE FASHION. LOW PRESSURE CENTERS
TYPICALLY ARE ASSOCIATED WITH BAD WEATHER.
SEVERE
THUNDERSTORM...A THUNDERSTORM THAT PRODUCES WIND GUSTS OF 58 MPH
OR GREATER...AND/OR HAIL 3/4 OF AN INCH OR LARGER
IN DIAMETER.
STATIONARY
FRONT..........A COLD FRONT OR WARM FRONT THAT HAS STOPPED
MOVING. THUNDERSTORMS CAN FORM ALONG STATIONARY
FRONTS WHEN THE AIR IS UNSTABLE.
SUPERCELL
THUNDERSTORM...A SEVERE THUNDERSTORM WITH A ROTATING UPDRAFT.
WHILE ANY THUNDERSTORM CAN PRODUCE A TORNADO...
SUPERCELL STORMS CAN PRODUCE LARGE AND LONG LIVED
TORNADOES.
SQUALL LINE....A LINE OF THUNDERSTORMS...USUALLY FORMED ALONG
A COLD FRONT OR DRY LINE.
THUNDERSTORM
OUTFLOW
BOUNDARY.......THE RAIN COOLED AIR THAT FLOWS OUT OF A
THUNDERSTORM CAN RESULT IN THE DEVELOPMENT OF A
SMALL SCALE COLD FRONT. NEW THUNDERSTORMS CAN FORM
ON THE BOUNDARIES OF OLD STORMS.
TORNADO........A RAPIDLY ROTATING COLUMN OF AIR IN CONTACT WITH
THE GROUND. WIND SPEEDS IN A TORNADO CAN BE
AS HIGH AS 300 MPH.
TROUGH OF
LOW PRESSURE...AN ELONGATED AREA OF LOWER BAROMETRIC PRESSURE.
THUNDERSTORMS CAN FORM NEAR THESE TROUGHS.
UPPER-LEVEL
DISTURBANCE....A CENTER OR TROUGH OF LOW PRESSURE IN THE UPPER
LEVELS OF THE ATMOSPHERE.
WARM FRONT.....A TRANSITION ZONE THAT MARKS WHERE WARMER AIR
IS MOVING INTO COLDER AIR. THUNDERSTORMS CAN FORM
ALONG A WARM FRONT WHEN THE ATMOSPHERE IS MOIST AND
UNSTABLE.
WIND
PROFILE........THE WAY THE WIND CHANGES WITH HEIGHT ABOVE THE
GROUND. A WEATHER PATTERN THAT RESULTS IN
THE WIND SPEED INCREASING WITH HEIGHT AND THE WIND
DIRECTION CHANGING IN A CLOCKWISE FASHION WITH
HEIGHT IS FAVORABLE FOR LONG LIVED SEVERE WEATHER
OUTBREAKS AND TORNADOES.
WHILE TODAY MARKS THE RESUMPTION OF ROUTINE THUNDERSTORM
OUTLOOKS...THESE OUTLOOKS ARE ISSUED ANYTIME DURING THE YEAR WHEN
SIGNIFICANT SEVERE WEATHER EPISODES ARE EXPECTED. ALSO...THE
THUNDERSTORM OUTLOOKS WILL OCCASIONALLY BE ISSUED PRIOR TO 130 PM
WHEN THE STORMS ARE EXPECTED TO OCCUR BEFORE THE EARLY AFTERNOON
HOUR...OR WHEN HEIGHTENED AWARENESS IS DESIRED.
BY USING THE OUTLOOKS IT IS HOPED THAT THE MEDIA...EMERGENCY
MANAGEMENT AGENCIES AND SPOTTERS CAN MORE EFFECTIVELY PLAN THEIR
ACTIVITIES AND BE READY WHEN SEVERE WEATHER THREATENS EASTERN
OKLAHOMA.
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