Severe Thunderstorm Warning 9, NWS Aberdeen, SD

AREA FORECAST DISCUSSION FOR CENTRAL/N-EAST SD AND W-CENTRAL MN
NATIONAL WEATHER SERVICE ABERDEEN SD
340 PM CDT THU JUN 6 2002

FORECAST CONTINUES TO BE TRICKY WITH THE ETA AND AVN STILL DIFFERING
ON SOME FEATURES. WILL LEAN JUST A BIT MORE TOWARD THE
ETA...ESPECIALLY FOR PRECIP AMOUNTS...WITH SOME BLEND OF THE AVN AS
WELL. A STRONG UPPER LOW WILL SPIN OVER WESTERN CANADA TONIGHT AND
FRIDAY BEFORE BEGINNING TO SLIDE SOUTHWARD FRIDAY NIGHT. THE LOW
BECOMES MORE OF AN ELONGATED TROUGH OVER THE ROCKIES BY SATURDAY
EVENING AND REMAINS THERE THROUGH MONDAY MORNING.

THE SURFACE TROUGH/FRONT CURRENTLY SLOWLY MOVING THROUGH THE CWA
WILL BE OVER THE SOUTH DAKOTA/NEBRASKA BORDER ON FRIDAY...WITH THE
SURFACE LOW OVER WESTERN NEBRASKA INTENSIFYING. HIGH PRESSURE WILL
NOSE INTO THE NORTHERN CWA TONIGHT...WITH THE MAIN INSTABILITY
REMAINING OVER THE FAR EASTERN CWA. WILL KEEP A MENTION OF
THUNDERSTORMS OVER THAT AREA FOR THIS EVENING. ETA INDICATED SOME
STABILIZING OF THE ATMOSPHERE ON FRIDAY FROM THE WEAK HIGH OVER THE
AREA. BY LATE IN THE AFTERNOON...THE FRONT BEGINS TO MAKE ITS WAY
BACK TO THE NORTH AND DECENT MOISTURE BEGINS TO STREAM BACK WITH IT.
WILL KEEP THE CHANCE FOR THUNDERSTORMS MENTIONED FOR FRIDAY
AFTERNOON AND EVENING. A DECENT SURFACE BOUNDARY REMAINS NEAR THE
AREA ON SATURDAY AND SUNDAY...WITH THE MODELS INDICATING DECENT
MOISTURE AND INSTABILITY WITH IT...SO SEE NO REASON TO REMOVE THE
MENTION OF THUNDERSTORMS FOR THOSE TWO DAYS. BASICALLY...THIS
FORECAST PERIOD WILL BE A COMBINATION OF UNSTABLE CONDITIONS AND A
BOUNDARY IN THE REGION. SO...THUNDERSTORMS ARE BOUND TO OCCUR EACH
DAY WITH JUST THE TIMING BEING THE QUESTION.

.EXTENDED DISCUSSION...

CONFIDENCE IN EXTENDED PERIOD REMAINS ELUSIVE TODAY.  WILL GO WITH
THE FLOW USING THE BEST COMPROMISE AND WAIT FOR REFINING MODEL
RUNS.  PERIOD OPENS WITH WESTERN UPPER LOW MOVING OUT OF THE FOUR
CORNERS REGION TOWARD THIS AREA.  MOISTURE FEED SETS UP AHEAD OF
SYSTEM AND OLD BAROCLINIC ZONE LINGERS GIVING CONVECTION AND
PRECIPITATION A FOCUS POINT.  WILL GO PRETTY CLOSE TO GOING FORECAST
AS CURRENT MODEL RUN GIVES NO REASON YET TO DOUBT TIMING. WILL DELAY
ENDING OF PRECIPITATION SLIGHTLY OTHERWISE LITTLE CHANGE.
TEMPERATURES LOOK TO STAY SEASONAL THROUGH THE PERIOD.

.ABR...NONE.

PARKIN/KEEFE