Damaging Wind in South Dakota, August 20, 2002

AREA FORECAST DISCUSSION...CORRECTION FOR DATE
NATIONAL WEATHER SERVICE SIOUX FALLS SD
230 PM CDT TUE AUG 20 2002

...ALL EYES ON IMPENDING SEVERE WEATHER/HEAVY RAIN EVENT...

SYNOPSIS...MORNING UPPER AIR ANALYSIS INDICATED STRONG UPPER TROUGH
DIGGING INTO THE PACIFIC NORTHWEST. SD SEEMED TO BE IN THE RIGHT
REAR QUAD OF A 70 KNT JET STRETCHING FROM ND SOUTHEAST INTO THE
GREAT LAKES. THIS IS LIKELY RESPONSIBLE FOR ONGOING CONVECTION OVER
N-CNTRL SD. AT H5 SEVERAL SHORT WAVES WERE NOTED MOVING THROUGH THE
ROCKIES...WITH THE FIRST OVER EASTERN WY...AND THE SECOND STRONGER
WAVE INTO CO/NM. LOW LEVEL MOISTURE WAS COPIOUS ACROSS THE CNTRL
PLAINS WITH AN H7 DP OF 9 ON THE KOAX 12Z SOUNDING. MID LEVEL TEMPS
WERE WARMING ACROSS THE WESTERN HIGH PLAINS WITH +16 THIS MORNING AT
KUNR. THIS WAS CONTINUING TO CAP SB CONVECTION ACROSS THE NORTHERN
PLAINS.

FORECAST...DIFFICULT FORECAST WITH A COUPLE DAYS OF CONVECTION
AHEAD...AND MODELS ARE HAVING A HARD TIME KEEPING VORT MAXES
STRAIGHT. PLENTY OF INSTABILITY COMING NORTH WITH THE WARM FRONT. AT
18Z WARM FRONT WAS LOCATED FROM SOUTHWEST SD SE INTO EAST CNTRL NEB.
THUNDERSTORMS WERE CONTINUING TO DEVELOP IN WAA ZONE NORTH OF THE
WARM FRONT. ELEVATED HAILERS POSSIBLE NORTH OF THE FRONT THIS
EVENING AS UPDRAFTS TAP SOME WARM MOIST UNSTABLE AIR FEEDING OVER THE
BOUNDARY. MAY BE DIFFICULT TO GET SB INITIATION ALONG THE WARM
FRONT...BUT IS MOST LIKELY IN THE AREA OF STRONGEST CONVERGENCE OVER
THE FAR SOUTHWEST CWA. IF SB CONVECTION CAN DEVELOP...ALL PARAMETERS
POINT TO SUPERCELLS WITH LOW LEVEL THERMODYNAMICS WOULD ALLOW FOR
ISOLATED TORNADOES. OTHERWISE EXPECT LLJ TO KICK IN AND FEED A
SEVERE MCS OVERNIGHT. HEAVY RAIN THREAT IS FAIRLY HIGH OVER OVER THE
NORTHERN AND EASTERN CWA. WILL NOT ISSUE FLOOD WATCH DUE TO THE LACK
OF HEAVY RAIN OVER THE THAT AREA OVER THE LAST COUPLE OF WEEKS.

THUNDERSTORMS WILL EXIT THE CWA TO THE EAST WEDNESDAY MORNING AND
WILL CONTINUE MORNING POPS. THEN QUESTION TURNS TO REDEVELOPMENT IN
THE AFTERNOON ALONG THE BOUNDARY. FEEL AT THIS TIME IT IS UNLIKELY.
WARMING MID LEVEL TEMPS AND LITTLE IF ANY UPPER SUPPORT WILL KEEP
THINGS IN CHECK. WILL GO DRY DURING THE DAY TOMORROW. TOMORROW NIGHT
EXPECT A MCS TO DEVELOP OVER THE WESTERN HIGH PLAINS AND TRACK TO
THE SOUTHEAST DURING THE NIGHT. WILL RUN PRETTY HIGH POPS TOMORROW
NIGHT AND ALSO MENTION HEAVY RAIN WITH PWATS OVER 2 INCHES. MAY HAVE
TO CONSIDER A FLOOD WATCH FOR TOMORROW NIGHT IN THE SOUTHERN CWA
WHERE MORE HEAVY RAIN HAS FALLEN OVER THE PAST COUPLE OF WEEKS.

EXTENDED...LITTLE CHANGE TO THE EXTENDED. FEEL MRF IS RETROGRADING
UPPER LOW OVER PAC NW TO MUCH...WITH A REX BLOCK DEVELOPING. THIS
WILL ALLOW FOR UPPER HEIGHTS TO FALL OVER THE NORTHERN PLAINS BY THE
END OF THE WEEK. THIS WILL ALLOW FOR THE ACTIVE SFC BOUNDARY TO SAG
SOUTH OF THE AREA. WILL CONTINUE A DRY EXTENDED.

OZF OUT BY 300 PM. THANKS FOR GREAT COORD FROM OMA AND MSP

.FSD...NONE

BOUSTEAD

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
828 PM CDT TUE AUG 20 2002

TIME(CDT)  .....CITY LOCATION.....STATE   ...EVENT/REMARKS...
           ....COUNTY LOCATION....

0732 PM    8 N PLANKINTON            SD   .75 INCH HAIL
08/20/02   AURORA                         REPORTED BY STORM
                                          SPOTTER.

0735 PM    5 ESE LETCHER             SD   1 INCH HAIL
08/20/02   SANBORN                        REPORTED BY STORM
                                          SPOTTER.

0757 PM    7 NNW MT VERNON           SD   .75 INCH HAIL
08/20/02   DAVISON                        REPORTED BY STORM
                                          SPOTTER.

0807 PM    8 NNE MT VERNON           SD   .88 INCH HAIL
08/20/02   DAVISON                        REPORTED BY STORM
                                          SPOTTER.

0808 PM    1 N LOOMIS                SD   .75 INCH HAIL
08/20/02   DAVISON                        REPORTED BY STORM
                                          SPOTTER.

0820 PM    5 SW MITCHELL             SD   1.75 INCH HAIL
08/20/02   DAVISON                        REPORTED BY STORM
                                          SPOTTER.