Severe Thunderstorm Warning 211, NWS Aberdeen, SD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ABERDEEN SD
230 PM CDT MON SEP 12 2005

.SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT
MAIN CONCERNS IN THE SHORT RANGE ARE PCPN TNT.  ONE DECENT WAVE/TROF
LIFTING DUE NORTH ACROSS CWA ATMT.  MEANWHILE ANOTHER FORECAST TO
LIFT ACROSS STATE LATE TONIGHT.  PRESENTLY LL BOUNDARY EXTENDS FROM
WC MN SOUTHWEST INTO SC SD.  SFC BASED INDICES OFF LAPS INDICATE A
MOIST AND UNSTABLE AIRMASS WITH LITTLE CAP OVER SOUTHEAST SOUTH
DAKOTA. OVER MY CWA REMAINS ONLY MILDLY UNSTABLE AND LATEST NAM
SUGGESTS THAT MUCAPES DONT CLIMB MUCH ACROSS CWA INTO THIS EVENING.
HOWEVER STILL PLENTY OF SHEAR TO WORK WITH ALONG AND JUST NORTH OF
THE BOUNDARY AND THUS A FEW SEVERE STORMS ARE STILL POSSIBLE...ALSO
MIGHT SEE SOME ADVECT NORTH INTO CWA OUT OF SOUTHERN SD THIS
EVENING.  DRIER AND COOLER AIR FILTERS SOUTH INTO THE REGION FOR
TUESDAY AND WEDNESDAY.  HOWEVER MIGHT SEE ISOLATED INSTABILITY
SHOWERS ON TUESDAY AFTERNOON AND EARLY EVENING AS COLD AIR AROUND H7
FILTERS ACROSS FORECAST AREA AND H85-H5 LAPSE RATES STEEPEN UP.
THIS ACTIVITY SHOULD DIE QUICKLY WITH LOSS OF DIABATIC HEATING
TUESDAY EVENING.  WEDNESDAY SHOULD BE NICE DAY.  WED NIGHT THROUGH
THURSDAY IS WHERE FORECAST GETS A LITTLE TRICKIER.  GFS AND NAM BOTH
NOW HINT AT MAINLY NOCTURNAL ACTIVITY WITH DEVELOPMENT OF LLJ BOTH
NIGHTS AS S/WS ALOFT PASS OVER THE REGION IN QUICK MID LEVEL FLOW.

.LONG TERM...FRIDAY THROUGH MONDAY
FORECAST CHALLENGES INCLUDE FLOW PATTERN EVOLUTION/TRENDS AND
TEMPS/PRECIP.

DEPENDING ON WHICH FLOW PATTERN TRANSPIRES WILL MAKE A BIG
DIFFERENCE IN PRECIP CHANCES AND TEMPS. LATEST GFS AND EC TRENDS
SUGGEST LARGE POLAR VORTEX NORTH OF HUDSON BAY WILL INFLUENCE THE
FLOW PATTERN OVER THIS CWA AT THE START OF THE PERIOD WITH FAST
ZONAL FLOW OVERHEAD. TEMPERATURE FORECAST DAY 4 SHOULD BE NEAR
SEASONAL NORMS...BUT AS UPPER LEVEL ENERGY SLIDES SOUTH ALONG
BRITISH COLUMBIA COAST AND MAKES A TURN EASTWARD ACROSS THE PAC
NW...SHOULD SEE SOME HEIGHT RISES ACROSS THIS FORECAST AREA...ALONG
WITH SOME WAA FOR LIGHT FRIDAY INTO SATURDAY. MODELS HAVING TROUBLE
RESOLVING THE FLOW PATTERN FROM THAT POINT ON. ONE DATA SET OF
SOLUTIONS RECENTLY PRODUCED A RATHER PROGRESSIVE PUSH OF THIS UPPER
LEVEL ENERGY ACROSS NORTHERN PLAINS BY SUNDAY NIGHT...WITH WARM AIR
STICKING AROUND CLEAR THROUGH SUNDAY...BEFORE A COLD FROPA AND CAA
SET UP ON MONDAY. ANOTHER DATA SET OF SOLUTIONS SETS UP THIS PAC NW
UPPER LOW SOUTH OF AN UPPER LEVEL RIDGE /A REX BLOCK PATTERN/ AND
SLOWS THE EASTWARD PROGRESSION OF THE SYSTEM WAY DOWN...WHILE
ALLOWING ENERGY OVER WESTERN CANADA TO RIDE DOWN THE BACK SIDE OF
THE UPPER RIDGE...DRAGGING A COLD FRONT ACROSS THIS FORECAST AREA BY
SUNDAY MORNING...RESULTING IN COOLER CONDITIONS FOR BOTH SUNDAY AND
MONDAY. FOR NOW...WITH BOTH THE GFS AND EC FLIP-FLOPPING BETWEEN
THESE AFOREMENTIONED SOLUTIONS HAVE OPTED TO LEAVE EXTENDED PERIODS
DRY...AND BLEND SUNDAY INTO COOLER OVER THE NORTHEAST CWA AND WARMER
OVER THE SOUTHWEST...WHICH WAS THE PREFERRED APPROACH IN HPC
GUIDANCE TODAY.

&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
&&

TDK/ALD

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE ABERDEEN SD
532 AM CDT MON SEP 12 2005

MNZ039-046-SDZ003>011-015>023-033>037-045-048-051-131045-
TRAVERSE-BIG STONE-CORSON-CAMPBELL-MCPHERSON-BROWN-MARSHALL-
ROBERTS-WALWORTH-EDMUNDS-DAY-DEWEY-POTTER-FAULK-SPINK-CLARK-
CODINGTON-GRANT-HAMLIN-DEUEL-STANLEY-SULLY-HUGHES-HYDE-HAND-JONES-
LYMAN-BUFFALO-
532 AM CDT MON SEP 12 2005 /432 AM MDT MON SEP 12 2005/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL
SOUTH DAKOTA...CENTRAL SOUTH DAKOTA...NORTHEAST SOUTH DAKOTA AND
WEST CENTRAL MINNESOTA.

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS ALONG A LINE FROM PIERRE TO WATERTOWN WILL
MOVE NORTH VERY EARLY THIS MORNING. THIS ACTIVITY WILL CONTINUE
TO MOVE NORTH OVER THE NEXT SEVERAL HOURS...PRODUCING BRIEF HEAVY
RAIN...FREQUENT LIGHTNING...AND POSSIBLY SOME SMALL HAIL. MORE
SHOWERS AND THUNDERSTORMS ARE EXPECTED THROUGHOUT THE DAY ACROSS
EASTERN SOUTH DAKOTA WITH LIGHTNING AND HAIL BEING THE MAIN
THREATS. THERE IS A SLIGHT RISK FOR SEVERE WEATHER ACROSS THE
AREA. TONIGHT ANOTHER DISTURBANCE WILL MOVE INTO THE WESTERN
DAKOTAS. THUNDERSTORMS WILL BE POSSIBLE ACROSS CENTRAL SOUTH
DAKOTA WITH LIGHTNING BEING THE MAIN THREAT.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

A CHANCE OF THUNDERSTORMS EXISTS FOR WEDNESDAY NIGHT WITH
LIGHTNING BEING THE MAIN THREAT.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BECOME NECESSARY THIS AFTERNOON...MAINLY
SOUTH OF A LINE FROM PIERRE TO SUMMIT.

TMT

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ABERDEEN SD
341 PM CDT MON SEP 12 2005

SDZ018>023-130200-
CLARK-CODINGTON-DEUEL-GRANT-HAMLIN-SPINK-
341 PM CDT MON SEP 12 2005

...THE NATIONAL WEATHER SERVICE HAS ISSUED TORNADO WATCH 778 IN
EFFECT UNTIL 9 PM CDT FOR THE FOLLOWING AREA...

IN SOUTH DAKOTA THIS WATCH INCLUDES 6 COUNTIES

IN NORTHEAST SOUTH DAKOTA

CLARK... CODINGTON... DEUEL...
GRANT... HAMLIN... SPINK...

THIS INCLUDES THE CITIES OF...CASTLEWOOD...CLARK...CLEAR LAKE...
MILBANK...REDFIELD AND WATERTOWN.

TDK