SPC MESOSCALE DISCUSSION 1712 FOR WRN/CENTRAL SD AND SRN ND
CONCERNING...SEVERE THUNDERSTORM WATCH 643...

VALID 310348Z - 310500Z

BASED ON CURRENT MOTION A NEW SEVERE THUNDERSTORM WATCH WILL LIKELY
BE NEED FOR PORTIONS OF NORTH CENTRAL SD AND SRN ND. 

A BOW ECHO COMPLEX WITH A HISTORY OF WIND DAMAGE CONTINUE TO MOVE
NEWD AT 45 KT THROUGH PORTIONS OF WRN SD. THE STRONGEST STORMS WERE
LOCATED IN ZIEBACH/HAAKON/STANLEY/DEWEY COUNTIES IN SD. THESE
STORMS ARE FORWARD PROPAGATING INTO THE NELY SURFACE FLOW WITH
DEWPOINTS IN THE LOW TO MID 70S. ALSO A WELL ORGANIZED COLD POOL
HAS DEVELOPED BEHIND THE BOW AND THE LOW LEVEL JET HAS INCREASED TO
50 KT SOUTH OF THIS SYSTEM. THE THREAT FOR DAMAGING WINDS WITH THIS
SYSTEM ARE EXPECTED TO CONTINUE FOR MUCH OF TONIGHT AS THE STORMS
MOVE NEWD ALONG FRONTAL BOUNDARY THAT EXTENDS NEWD INTO SOUTH
CENTRAL ND. 

THE REFLECTIVITY CORES HAVE INCREASED IN THE PAST HOUR...SUGGESTING
THE STORMS ARE INGESTING A MORE UNSTABLE AIR MASS THAN EARLIER AND
THIS MAY RESULT IN STRONGER DOWNDRAFTS AND AN INCREASED RISK FOR
DAMAGING WIND TO EXCEED 65-75 KT. 

CURRENT MOTION PLACES THE BOW ECHO NEAR THE SD/ND BORDER COUNTIES
BY 05Z AND A NEW SEVERE THUNDERSTORM WATCH LIKELY WILL BE ISSUED
SHORTLY. 

..IMY.. 07/31/01