Severe Thunderstorm Warning 359, NWS Sioux Falls, SD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
302 PM CDT WED AUG 21 2002

SYNOPSIS...MORNING SUBJECTIVE UPPER AIR ANALYSIS INDICATED A TROUGH
OVER THE WESTERN US...WITH A RIDGE OVER THE MISSISSIPPI RIVER
VALLEY. SEVERAL JET MAXIMA WERE NOTED AT H3...WITH ONE OVER EASTERN
NEW MEXICO AND ANOTHER EXTENDING FROM WYOMING WESTWARD TO ARIZONA.
AT H7...SIGNIFICANT MOISTURE REMAINED ACROSS THE CENTRAL PLAINS WITH
ANOTHER 9 C DP AT KOAX AT H7. MAIN SHORT WAVE FOR OUR CWA WAS ANALYZED
OVER EASTERN CO/NM. 18Z SUBJECTIVE SFC ANAL INDICATES LOW PRESSURE
OVER THE SD/NE BORDER WITH AN OUTFLOW BOUNDARY EXTENDING EAST INTO
NW IA. THE WARM FRONT IS FARTHER N OF THIS...EXTENDING ALONG AND
NORTH OF I-90.

FORECAST...MCV CAN BE SEEN SPINNING AROUND SE SD IN THE VIS SAT
IMAGES THIS AFTERNOON. ATMOSPHERE IS VERY MOIST AND UNSTABLE THIS
AFTERNOON WITH SFC DPS IN THE 70S...AND TEMPS IN THE SRN CWA RISING
INTO THE 80S. LATEST RUC GUIDANCE INDICATES THAT ATMOSPHERE IS
WEAKLY CAPPED (< -25 J/KG) IN THE AREAS WHERE TEMPS ARE IN THE
80S...AND 50 MB MLCAPE VALUES ARE ON THE ORDER OF 2000 J/KG. UPPER
LEVELS ARE LENDING LITTLE SUPPORT TO CONVECTIVE INITIATION...BUT
SUSPECT THAT CONVERGENCE ALONG THE FRONT WILL INITIATE SOME ISO/SCT
TRW LATE THIS AFTERNOON AND EVENING. WILL RUN THE BEST POPS IN THE
SOUTHER CLOSES TO REGION OF BEST VERTICAL MOTION FROM NM/CO SHORT
WAVE. PRECIP WATER NEAR OR SLIGHTLY OVER 2 INCHES SO WILL MENTION
LOCALLY HEAVY RAIN. NOT EXPECTING WIDESPREAD HEAVY RAIN AND THUS NO
FLOOD WATCH NEEDED.

STORMS CLEAR OUT OF THE SOUTHEAST TOMORROW LEAVING THE CWA DRY. AS
UPPER HEIGHTS FALL OVER THE NORTHERN PLAINS...ACTIVE SFC FRONT WILL
SLOWLY SAG TO THE SOUTH. MODELS BRING SHORT WAVE ACROSS FRONT ON
THURSDAY...AND WILL INCLUDE SOME LOW CHC POPS FOR THE EXTREME SOUTH
FOR THIS BY LATE AFTERNOON AND EVENING. THINGS CLEAR OUT THURSDAY
NIGHT...AND NEW GUIDANCE POINTS TO A DRY FRIDAY WITH THE ACTIVE
FRONT WELL OFF TO OUR SOUTH IN THE CNTRL PLAINS. THUS WITH CWA IN
DRIER NE LO LVL FLOW WILL GO DRY...AND BRING IN MORE SUN.

MAY HAVE SOME FOG PROBLEMS THE NEXT TWO NIGHTS WITH ALL THE LOW
LEVEL MOISTURE AROUND...AND FAIRLY LIGHT WINDS OVERNIGHT. FEEL AT
THIS POINT THE BETTER NIGHT WILL BE THURSDAY NIGHT WITH THE CLEAR
SKIES. THUS WILL NOT INCLUDE FOR TONIGHT...AND LET NEXT SHIFT DECIDE
ON THURSDAY NIGHT. TEMPERATURES THE NEXT COUPLE OF DAYS WILL BE SLOW
TO RISE IN THE AFTERNOON WITH SOUTHEAST LO LEVEL FLOW NOT ALLOW FOR
MUCH WARMING. WILL GENERALLY SPLIT THE DIFFERENCE IN THE GUIDANCE
FOR OVERNIGHT LOWS.

EXTENDED...SOME DIFFERENCES IN THE MODELS WITH WHAT TO DO WITH THE
UPPER LOW OVER THE PACIFIC NORTHWEST. WILL GENERALLY FOLLOW THE
ENSEMBLE MEAN THROUGH THE EXTENDED. AT THIS POINT WILL LEAVE THE
EXTENDED DRY WITH THE CONTINUED UNCERTAINTY. TEMPS WILL GENERALLY BE
NEAR CLIMO FOR THIS TIME OF YEAR.

OZF OUT BY 330 PM.

.FSD...NONE

BOUSTEAD

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
230 PM CDT WED AUG 21 2002

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

0930 PM    EMERY                     SD   60 MPH TSTM GUST
08/20/02   HANSON                         SMALL TREE LIMBS DOWN

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
413 PM CDT WED AUG 21 2002

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

0830 AM    BEAVER CREEK              MN   FLOOD
08/21/02   ROCK                           REPORTED BY PUBLIC.
                                          SUBSTANTIAL FLOODING
                                          ALONG SPRING CREEK
                                          ALONG GOLF COURSE.
                                          DESTROYED SEVERAL OF
                                          THE HOLES.

IAZ001>003-MNZ071-072-080-081-089-090-097-098-SDZ040-056-062-067-
212300-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
438 PM CDT WED AUG 21 2002

AT 430 PM CDT...A TRAINED SPOTTER REPORTED A FUNNEL CLOUD JUST SOUTH
OF MARSHALL IN LYON COUNTY MINNESOTA. THIS FUNNEL IS IN FRONT OF A
WEAK COLD FRONT WHICH STRETCHES FROM JUST NORTH OF THE TWIN CITIES...
BACK TO NORTH CENTRAL NEBRASKA. THE AIR FLOW BOTH AT THE SURFACE AND
ALOFT IS WEAK WITH A TROPICAL AIR MASS IN PLACE. WHAT CAUSES THESE
FUNNELS...IS THAT AN UPDRAFT OF AIR GETS STARTED AHEAD OF THIS
FRONT...WITH LITTLE IN THE WAY OF FLOW TO DISTURB THE UPDRAFT. THE
UPDRAFT GETS STRETCHED...BEGINS TO ROTATE AND THUS THERE ARE YOUR
FUNNEL CLOUDS.

THESE FUNNELS ARE SHORT LIVED...RARELY REACH THE GROUND...AND POSE
LITTLE OR NO THREAT TO PERSONAL SAFETY. THERE ARE NUMEROUS SMALL
ECHOES BEING DETECTED BY SIOUX FALLS NATIONAL WEATHER SERVICE RADAR
LATE THIS AFTERNOON...ACROSS THE I 29 CORRIDOR OF SOUTHEAST SOUTH
DAKOTA...IN SOUTHWEST MINNESOTA...AND THE EXTREME NORTHWEST CORNER OF
IOWA. ANY ONE OF THESE CLOUDS COULD PRODUCE A SHORT LIVED FUNNEL.
FURTHER SOUTH INTO THE REST OF NORTHWEST IOWA AND THE YANKTON AREA...
THE FLOW ABOVE THE SURFACE IS STRONGER WHICH WILL ACT TO DISTURB
THESE WEAK UPDRAFTS...AND THERE IS ALSO LESS INTERACTION WITH THE
WEAK FRONT. THEREFORE...THE POSSIBILITY OF FUNNELS IS LESS IN THESE
AREAS.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
721 PM CDT WED AUG 21 2002

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

0715 PM    5 N DALLAS                SD   60 MPH TSTM GUST
08/21/02   GREGORY                        REPORTED BY PUBLIC.
                                          TREE BRANCHES DOWN.