Severe Thunderstorm Warning 155, NWS Rapid City, SD

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY...UPDATED
NATIONAL WEATHER SERVICE RAPID CITY SD
320 PM MDT SUN AUG 25 2002

WATER VAPOR DEPICTS UPR LOW OVR MT...WITH WEAK RIDGING EXTENDING
NORTH THROUGH THE CNTRL ROCKIES. SFC TROF DVLPG IN THE LEE OF
ROCKIES...WITH HIGH PRESSURE OVR CNTRL PLAINS RESULTING IN RETURN
FLOW ACRS CWFA. STRONG CONVECTION STARTING TO FIRE OVR ERN MT AND
WRN ND.

WILL CONT TO SEE ISOLD PULSE TSTMS OVR BLKHLS INTO THIS EVE AS CAP
HAS ERODED. AMS HAS DRIED AND MID-LVL FLOW PICKED UP...THEREFORE
THREAT OF HEAVY RAINS AND SLOW MOVG TSTMS IS MINIMAL THIS EVE. TSTM
ACTIVITY WILL LIKELY CONT TO DVLP ACRS ERN MT AND WRN ND. 18Z
ETA/RUC BEGINNING TO PICK UP ON THIS ACTIVITY AND SPRDG IT E/SE
TNGT.  CORFIDI VECTORS SUGGEST IF THIS ACTIVITY EVOLVES INTO MCS IT
WILL TRAVEL ESE...AFFECTING NWRN ZONES. ADDITIONALLY...LO LVL JET
INCREASES LATER TONIGHT ACRS SRN ZONES WITH MUCAPE VALUES OF
1000-1500J/KG ALG WITH GOOD THETA-E ADVECTION. THEREFORE IF AN MCS
DVLPS IT WILL HAVE THE POTENTIAL TO DVLP SWD ACRS ERN HALF OF ZONES.
HOWEVER...IF MCS REMAINS TOO FAR NORTH...THERE WILL STILL BE DECENT
SHOT OF SEEING ISOLD CONVECTION ACRS SRN/ERN ZONES AS ENOUGH UVV
WILL BE IN PLACE.

UPR LVL TROFING REMAINS THE DOMINANT FEATURE FROM THE PAC NW TO NRN
ROCKIES THRU MID WEEK. IT WILL BE QUITE DIFFICULT TO TIME/POSITION
SHORT WAVES EMBEDDED IN UNSTABLE SW FLOW...THEREFORE CHC OF POP
WARRANTED THROUGH ENTIRE 1-3 DAY FCST. TEMPS WILL REMAIN FAIRLY
CONSISTENT DURING THIS PD AS WELL.

EXTENDED...CONTD TROFING WITH UNSETTLED WX PATTER EXPECTED THROUGH
FRI...WITH LONGER RANGE GUIDANCE SHOWING SOME HINT OF SHORT WAVE
RIDGING ON SAT. A MORE PROGRESSIVE TROF SWINGS THRU NRN PLAINS DAY 7
FOR RETURN TO UNSETTLED WX AND SLIGHT COOL DOWN.

.UNR...NONE
JOHNSON