SPC MESOSCALE DISCUSSION 1516 FOR ERN AND SERN MT
CONCERNING...SEVERE THUNDERSTORM WATCH 557...

VALID 150033Z - 150230Z

SEVERE THUNDERSTORM WATCH 557 CONTINUES IN EFFECT ACROSS SERN MT
WITH SCATTERED CELLULAR THUNDERSTORMS MOVING GENERALLY ENEWD AT 25-
30KT. LARGE HAIL AND OCCASIONAL DAMAGING DOWNDRAFT WINDS ARE LIKELY
WITH THESE STORMS. ISOLATED SEVERE STORMS ARE ALSO POSSIBLE ALONG
AN E-W AXIS NORTH OF THE WATCH AREA FROM LWT EWD TO 25 W GDV. 

THE 15/00Z SOUNDINGS FROM GREAT FALLS AND RIVERTON INDICATE VERY
STEEP MID-LEVEL LAPSE RATES OF GREATER THAN 8 C/KM WHICH ARE LIKELY
ADVECTING ENEWD WITH 30-40KT 500MB FLOW ACROSS MT. MID-LEVEL FLOW
AND ASSOCIATED SHEAR IS MARGINALLY CONDUCIVE FOR SUPERCELLS AND
UPDRAFT ROTATION MAY ENHANCE POTENTIAL FOR LARGE HAIL ACROSS THE WW
557 AREA. MUCAPE VALUES RANGE FROM 2000-2500 J/KG. COMBINATION OF
LARGE-SCALE FORCING AHEAD OF SRN ID SHORTWAVE TROUGH AND MODERATE
INSTABILITY/STEEP MID-LEVEL LAPSE RATES SHOULD MAINTAIN SCATTERED
THUNDERSTORM COVERAGE ACROSS THE DISCUSSION AREA WITH THE POTENTIAL
FOR SEVERE STORMS THROUGH THE EVENING HOURS. 

..BANACOS.. 07/15/01