Severe Thunderstorm Warning 87, NWS Grand Forks, ND

SPECIAL WEATHER STATEMENT AND RADAR SUMMARY
NATIONAL WEATHER SERVICE FARGO ND
435 PM CDT MON AUG 17 1987

....THUNDERSTORMS INTENSIFYING OVER NORTHEAST NORTH DAKOTA....

AT 426 PM CDT...AN INTENSE THUNDERSTORM WITH VERY HEAVY RAIN AND PEA
TO MARBLE SIZE HAIL WAS JUST SOUTH OF THE GRAND FORKS AIR FORCE BASE
OR ABOUT 10 MILES WEST OF THE CITY OF GRAND FORKS IN NORTHEAST NORTH
DAKOTA. THIS STORM WAS MOVING SOUTHEAST AT 30 MILES AN HOUR AND SHOULD
CROSS THE RED RIVER INTO SOUTHWEST POLK COUNTY OF NORTHWEST MINNESOTA
BY 530 PM. PERSONS IN WESTERN POLK AND NORTHWEST NORMAN COUNTY OF
NORTHWEST MINNESOTA SHOULD BE ALERT FOR THESE INTENSE THUNDERSTORMS.

AT 415 PM CDT PEA TO MARBLE SIZE HAIL AND VERY HEAVY RAIN WAS REPORTED
AT EMERADO JUST SOUTH OF THE AIR BASE IN NORTHEAST NORTH DAKOTA.

OTHER SCATTERED SHOWERS AND THUNDERSTORMS WERE DEVELOPING OVER PARTS
OF NORTHEAST AND EAST CENTRAL NORTH DAKOTA AND EXTREME NORTHWEST AND
WEST CENTREAL MINNESOTA MOVING SOUTHEAST AT 30 MILES AN HOUR.

SPECIAL WEATHER STATEMENT AND RADAR SUMMARY
NATIONAL WEATHER SERVICE FARGO ND
535 PM CDT MON AUG 17 1987

....INTENSE THUNDERSTORMS OVER THE RED RIVER OF THE NORTH NEAR HALSTAD
    SHELLY AND CLIMAX....

AT 525 PM CDT...INTENSE THUNDERSTORMS...SOME WITH VERY HEAVY RAIN AND
SMALL HAIL WERE ALONG THE RED RIVER MOVING INTO NORTHWEST MINNESOTA.
THE MOST INTENSE THUNDERSTORMS WERE NEAR HALSTAD..SHELLY AND CLIMAX IN
EXTREME SOUTHWEST POLK AND NORTHWEST NORMAN COUNTIES OF NORTHWEST
MINNESOTA. THESE STORMS WERE MOVING EAST AT 30 MILES AN HOUR AND
PERSONS IN NORMAN AND POLK COUNTIES INCLUDING THE CITIES OF BELTRAMI..
ADA AND TWIN VALLEY CAN EXPECT THESE STORMS BY 630 PM.

OTHER SCATTERED SHOWERS AND THUNDERSTORMS..SOME WITH VERY HEAVY RAIN
WERE OVER PARTS OF EASTERN NORTH DAKOTA AND NORTHWEST MINNESOTA.

ONE STRONG THUNDERSTORM WITH VERY HEAVY RAIN HAD DEVELOPED OVER NORTH-
WEST BARNES COUNTY OF EAST CENTRAL NORTH DAKOTA WHICH WAS ABOUT 25 MILES
NORTHWEST OF VALLEY CITY. THIS STORM WAS MOVING EAST AT 30 MILES AN
HOUR AND SHOULD MOVE ACROSS NORTHERN BARNES INTO NORTHWEST CASS
COUNTY BY 630 PM.

MANY OF THESE INTENSE THUNDERSTORMS..ESPECIALLY THE ONES THAT WERE
CROSSING THE RED| RIVER INTO MINNESOTA HAVE PRODUCED VERY HEAVY RAIN
ALONG WITH SOME PEA TO MARBLE SIZE HAIL.
SPIES

SPECIAL WEATHER STATEMENT AND RADAR SUMMARY
NATIONAL WEATHER SERVICE FARGO ND
640 PM CDT MON AUG 17 1987

....INTENSE THUNDERSTORMS MOVING INTO THE SOUTHERN RED RIVER VALLEY....

AT 627 PM CDT...INTENSE THUNDERSTORMS..WITH VERY HEAVY RAIN AND SMALL
HAIL WERE MOVING INTO SOUTHEAST NORTH DAKOTA INCLUDING THE RED RIVER
VALLEY. SEVERAL INTENSE THUNDERSTORMS WERE OVER CASS COUNTY OF SOUTH-
EAST NORTH DAKOTA..INCLUDING ONE MOVING THROUGH THE SOUTHERN PORTION
OF FARGO/MOORHEAD. MOST OF THESE THUNDERSTORMS SHOULD MOVE ACROSS
CASS COUNTY INTO CLAY COUNTY OF NORTHWEST MINNESOTA BY 730 PM.

OTHER INTENSE THUNDERSTORMS..WITH VERY HEAVY RAIN AND SOME SMALL HAIL
WERE OVER NORTHWEST MINNESOTA..WHICH INCLUDE THE COUNTIES OF NORTHERN
CLAY..NORMAN AND MAHNOMEN. THESE THUNDERSTORMS WERE ALSO MOVING EAST
AT 30 MILES AN HOUR AND SHOULD MOVE INTO BECKER AND THROUGH NORMAN AND
MAHNOMEN COUNTIES BY 730 PM.

ANOTHER INTENSE THUNDERSTORM WITH VERY HEAVY RAIN WAS MOVING INTO
SOUTHWEST STEELE COUNTY OF EAST CENTRAL NORTH DAKOTA. THIS STORM WILL
MOVE EAST ACROSS SOUTHERN STEELE COUNTY..INCLUDING THE TOWNS OF HOPE
AND COLGATE BY 730 PM.

REMEMBER...MANY OF THESE INTENSE THUNDERSTORMS HAVE PRODUCED VERY HEAVY
RAIN..SMALL HAIL AND DANGEROUS LIGHTNING SO STAY ALERT AND BE READY
TO MOVE TO A PLACE OF SAFTEY IF THREATENING WEATHER APPROACHES.
SPIES

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE FARGO ND
705 PM CDT MON AUG 17 1987

...CONDITIONS FAVORABLE FOR COLD AIR FUNNELS OVER EAST CENTRAL NORTH
DAKOTA AND NORTHWEST AND WEST CENTRAL MINNESOTA...

SCATTERED INTENSE THUNDERSTORMS WERE MOVING THROUGH THE FARGO/MOORHEAD
AREA AND MAY PRODUCE A COLD AIR FUNNEL.

COLD AIR FUNNELS ARE NOT ASSOCIATED WITH SEVERE THUNDERSTORMS AS
ARE THE TYPE OF FUNNEL CLOUD THAT PRODUCES A TORNADO.  COLD AIR
FUNNELS ARE FORMED BY THUNDERSTORMS AND RAINSHOWERS WHEN UNIQUE
METEOROLOGICAL CIRCUMSTANCES ARE MET.  MILD UNSTABLE AIR IN THE
LOWER LEVELS OF THE ATMOSPHERE IS CAPPED BY COOL UNSTABLE AIR
ALOFT.  SIMILAR TO SEVERE THUNDERSTORMS...UP AND DOWN DRAFTS DEVELOP
IN THE ATMOSPHERE.  HOWEVER...THE DOWN DRAFTS ARE STRONGER THAN THE
THE UP DRAFTS AND ARE ABLE TO TAP THE COOLER AIR ALOFT PULLING IT
DOWN TOWARDS THE EARTHS SURFACE.  AS THE COOLER AIR FLOWS DOWN THROUGH
THE CLOUD IT BEGINS TO ROTATE.  THIS VERTICAL COLUMN OF ROTATING AIR
PROTRUDES THROUGH THE BASE OF THE CLOUD SINCE IT IS COOLER AND HEAVIER
THAN THE AIR AROUND IT.  THIS PRODUCES THE VISIBLE COLD AIR FUNNEL.

COLD AIR FUNNELS GENERALLY DO NOT REACH THE EARTHS SURFACE AND ARE
USUALLY NOT DANGEROUS.  HOWEVER...COLD AIR FUNNELS HAVE ON RARE OCCASION
TOUCHED THE GROUND AND CAUSED DAMAGE.  BECAUSE OF THIS...WHEN COLD AIR
FUNNELS ARE OBSERVED YOU SHOULD SEEK SHELTER IMMEDIATELY.  IF YOU ARE
ON A LAKE YOU SHOULD SEEK SAFE HARBOR UNTIL THE THUNDERSTORMS PASS YOUR
AREA.

CONDITIONS WILL REMAIN FAVORABLE FOR THE DEVELOPMENT OF COLD AIR FUNNELS
FOR THE NEXT SEVERAL HOURS.  IF YOU LIVE ACROSS EAST CENTRAL NORTH DAKOTA
OR NORTHWEST AND WEST CENTRAL MINNESOTA YOU SHOULD BE ALERT FOR THE
POSSIBLE DEVELOPMENT OF COLD AIR FUNNELS AND BE PREPARED TO MOVE TO A
SAFE PLACE.
EWENS

STORM REPORTS
NATIONAL WEATHER SERVICE FARGO ND
710 PM CDT MON AUG 17 1987

TIME      EVENT
415 PM    POLICE IN EMERADO NORTH DAKOTA-12 WEST OF GRAND FORKS-
          REPORTED TORRENTIAL RAIN AND 1/4 TO 1/2 INCH HAIL COVERING
          THE GROUND.  WIND GUSTED TO 44 MPH AT THE GRAND FORKS AIR
          BASE.

536 PM    FERTILE MINNESOTA CO OPERATIVE OBSERVER REPORTED VERY HEAVY
          RAIN AND PEA SIZED HAIL.

630-635PM PEA SIZED HAIL AND VERY HEAVY RAIN IN SOUTH FARGO AND PAGE
          NORTH DAKOTA AS WELL AS MOORHEAD MINNESOTA.

650 PM    MARBLE AND LARGER SIZED HAIL IN FLOM MINNESOTA..BY COOPERATIVE
          OBSERVER.

700 PM    PEA TO MARBLE SIZED HAIL AND BRIEF VERY HEAVY RAIN REPORTED
         AT HOPE NORTH DAKOTA.
EWENS