Severe Thunderstorm Warning 213, NWS Aberdeen, SD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ABERDEEN SD
830 PM CDT SAT SEP 29 2007

.UPDATE...
THUNDERSTORMS ARE BEGINNING TO FIRE ON LEADING EDGE OF DRYLINE IN
NEBRASKA AND PUSHING INTO EXTREME SOUTHCENTRAL SODAK. DID EDIT WX
GRIDS TO DELAY ONSET OF TSRA ACROSS NORTHCENTRAL AND NORTHEAST
SOUTH DAKOTA BY A FEW HOURS. TEMPS ARE STAYING UP WITH STRONG
SOUTH WINDS...SO TWEAKED HOURLY TEMP GRIDS AS WELL. REMAINDER OF
FORECAST LOOKS OK. ZONE UPDATE NOT NEEDED ATTM.

UPDATED AVIATION DISCUSSION BELOW.

&&
.PREV DISCUSSION...
.SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT
FORECAST CHALLENGES INCLUDE SEVERE WX POTENTIAL THIS
EVENING/OVERNIGHT...ALONG WITH TIMING AND AREAL COVERAGE OF RAIN
SHIELD LATE TONIGHT THROUGH SUNDAY.

PRESENTLY...THE MAKINGS OF A DRY LINE WITHIN A LEE-OF-THE-ROCKIES
SURFACE TROF ARE SHOWING UP ACROSS WESTERN SOUTH DAKOTA...WHERE
DEWPOINTS BEHIND THE SURFACE TROF ARE DROPPING THROUGH THE
30S...INTO THE UPPER 20S WHILE DEWPOINTS OUT AHEAD OF THIS NEARLY
STATIONARY SURFACE FEATURE ARE IN THE UPPER 40S TO MID 50S ALONG
THE MISSOURI RIVER VALLEY...WITH LOW TO MID 60S FOR DEWPOINTS OUT
OVER NORTHEAST SOUTH DAKOTA AND WEST CENTRAL MINNESOTA. SEVERAL
RECORD HIGH TEMPERATURES ARE IN JEOPARDY OF BEING TIED OR BROKEN
THIS AFTERNOON ACROSS CENTRAL SOUTH DAKOTA...WHERE TEMPERATURES
ARE WARMING INTO THE UPPER 80S TO LOWER 90S PRESENTLY. THERE IS
ALSO A COLD FRONT DEPICTED IN SURFACE ANALYSIS EXTENDING FROM NW
NORTH DAKOTA BACK INTO NE WYOMING AND NW COLORADO...MOVING RATHER
SLOWLY AT THIS TIME.

BOTH THE 12Z GFS AND NAM SOLUTIONS AGREE FOR THE MOST PART ON
SYSTEM TIMING/TRACK FOR LATER TONIGHT INTO SUNDAY. BOTH MODELS
WERE COMPARABLE ON SURFACE COLD FRONTAL TIMING TONIGHT AND
SUNDAY...WITH THE FRONT EXPECTED TO BE THROUGH KMBG AND KPIR BY OR
SHORTLY AFTER 1 AM CDT...BLASTING THROUGH KABR AROUND 6 AM CDT ON
SUNDAY AND THROUGH KATY BY 9 AM CDT ON SUNDAY. BOTH MODELS STILL
SHOWING PWATS CRANKED UP TO 1.25 TO 1.50 INCHES /MUCH ABOVE
NORMAL/ OVERNIGHT TONIGHT INTO SUNDAY MORNING...SO THE WX GRIDS
HAVE LOCALLY HEAVY RAINFALL POSSIBLE WORDING IN FOR TONIGHT INTO
SUNDAY MORNING. THE MODELS BRING SUBSTANTIVE LIFT/FORCING INTO
THIS FORECAST AREA...PRETTY MUCH...AFTER 00Z AND SHOW SAID LIFT
PERSISTING INTO SUNDAY MORNING THROUGHOUT MUCH OF THE CENTRAL
AND EASTERN FORECAST ZONES WHERE THE HIGHEST POPS RESIDE. PLENTY
OF MID-LEVEL INSTABILITY/STEEP LAPSE RATES SHOULD WORK IN
CONJUNCTION WITH FAVORABLE UPPER LEVEL JET SUPPORT TO PRODUCE
THUNDERSTORMS. THE SHEAR AND INSTABILITY SHOULD BE ENOUGH TO
STRENGTHEN SOME STORMS TO SEVERE LEVELS LATE THIS EVENING AND
OVERNIGHT...WHERE THE MAIN SEVERE THREATS WILL BE LARGE HAIL AND
DAMAGING WINDS.

THERE IS ACTUALLY A TROWAL FEATURE DEVELOPING NOW WITH THIS
SYSTEM ON SUNDAY AS THE LOW PRESSURE SYSTEM UNDERGOES LEE-OF-THE-
ROCKIES CYCLOGENESIS AND CLOSES OFF A MID-LEVEL CIRCULATION DURING
THE DAY ON SUNDAY ACROSS SERN SOUTH DAKOTA/NERN NEBRASKA. THIS
SHOULD HELP SHOWERY-TYPE RAINFALL PERSIST THROUGH A BETTER PART
OF THE DAY ON SUNDAY. DESPITE UNDERGOING CYCLOGENESIS...THIS
SYSTEM SHOULD SPEED OFF INTO THE GREAT LAKES REGION FAIRLY
QUICKLY. WHILE THE PRECIPITATION SHOULD BE FINISHED BY 00Z
MONDAY...THERE WILL STILL BE CAA LOW CLOUDS TO CONTEND WITH SUNDAY
NIGHT...WHERE SOME PATCHY LIGHT DRIZZLE WOULD NOT BE OUT OF THE
QUESTION. LEFT SUNDAY NIGHT WX GRIDS DRY FOR NOW THOUGH.

LOW TEMPERATURES TONIGHT ARE A BIT OF A PICKLE...WITH A COLD
FROPA IN PROGRESS OVERNIGHT AND LOTS OF CLOUDS AND PRECIP EXPECTED
TO WREAK HAVOC ON THE LOW TEMPERATURES. DURING THE DAY
SUNDAY...10 TO 15 DEGREES OF COOLING ARE FORECAST TO OCCUR IN LOW
LEVEL CAA. HIGH TEMPERATURES ARE ONLY EXPECTED TO TOP OUT IN THE
UPPER 50S TO MID 60S UNDER A PERSISTENT RAIN AND CLOUD
SHIELD...WHICH SHOULD BE COVERING MUCH OF THE FORECAST AREA ON
SUNDAY. EXPECTING CLOUDS TO STICK AROUND FOR A BETTER PART OF
SUNDAY NIGHT...SO CHOSE NOT TO KNOCK THE BOTTOM OUT FROM UNDER THE
LOW TEMPERATURES...DESPITE SURFACE HIGH PRESSURE BUILDING IN...AND
WINDS TURNING LIGHT AND VARIABLE SUNDAY NIGHT.

.LONG TERM...MONDAY MORNING THROUGH SUNDAY

AFTER A CHILLY START TO MONDAY MORNING UNDER DRY UPPER RIDGE AND
SURFACE HIGH PRESSURE...AS THESE FEATURES MOVE EAST A RETURN
SOUTHWESTERLY FLOW DEVELOPS AHEAD OF NEXT UPPER TROF. THIS
FEATURE WILL MOVE ACROSS THE CWA TUESDAY...FORCING SURFACE
TROF/FRONT ACROSS THE MISSOURI OVERNIGHT AND INTO THE EASTERN CWA
BY TUESDAY AFTERNOON. AREA OF HEAVY RAIN IS IDENTIFIED BY MOST
MODELS TO FORM ALONG THE EASTERN PERIPHERY OF THE CWA LATE TUESDAY.

100-120KT NORTHWEST PACIFIC JET GRADUALLY TRENDS EASTWARD FOR
WEDNESDAY...BECOMING A SOUTHWESTERLY JET BY THE END OF THE WEEK AS
IT INTERACTS WITH A DIGGING TROF OVER THE WESTERN CONUS. SERIES OF
WEAK DISTURBANCES WILL RIDE THE JET ACROSS THE NORTHERN
CONUS...TOO FAR NORTH TO IMPACT CWA.

AS UPPER TROF BEGINS TO MOVE INTO THE PLAINS STATES...STORM TRACK
DRIFTS SOUTHWARD OVER THE CWA. IF TIMING IS CONSISTENT THROUGH THE
WEEK...WE WILL BE LOOKING AT A WET WEEKEND. WITH MINOR
EXCEPTIONS...IE PERIODS OF FAVORABLE RADIATION COOLING OR EXCESSIVE
CLOUD COVER...TEMPERATURES WILL REMAIN CLOSE TO THE SEASONAL RANGE FOR
THE WEEK.

&&

.AVIATION...
LOOK FOR SCT-LIKELY TSRA TO DEVELOP FROM KPIR TO KABR BY 06Z
SUNDAY...CONT THROUGH 15Z SUNDAY. SOME TSRA COULD PRODUCE HAIL UP
TO 1 IN DIAMETER AS WELL AS WIND GUSTS TO 50 KTS. MVFR VSBYS IN
HEAVIER RAIN IS POSSIBLE. BY 15Z SUNDAY LOOK FOR VFR CIGS AOA 4K
TO 5K FT AGL WITH SCT-OCNL -SHRA...WITH -TSRA EXPECTED ALONG I-29
CORRIDOR.

&&

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

UPDATE...HINTZ
SHORT TERM...DORN
LONG TERM...CONNELLY
AVIATION...HINTZ

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE ABERDEEN SD
1119 AM CDT SAT SEP 29 2007

MNZ039-046-SDZ004>011-016>023-034>037-048-051-301630-
TRAVERSE-BIG STONE-CAMPBELL-MCPHERSON-BROWN-MARSHALL-ROBERTS-
WALWORTH-EDMUNDS-DAY-POTTER-FAULK-SPINK-CLARK-CODINGTON-GRANT-
HAMLIN-DEUEL-SULLY-HUGHES-HYDE-HAND-LYMAN-BUFFALO-
1119 AM CDT SAT SEP 29 2007

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

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORMS ARE EXPECTED TO DEVELOP AND EXPAND IN AREAL
COVERAGE THIS EVENING AND OVERNIGHT AS THEY MOVE EAST ACROSS THE
NORTHEASTERN HALF OF SOUTH DAKOTA AND INTO WEST CENTRAL
MINNESOTA. THE THREAT FOR SEVERE WEATHER WILL EXPAND EAST ACROSS
THE STATE DURING THE EVENING AND OVERNIGHT HOURS...WITH LARGE
HAIL AND DAMAGING WINDS THE PRIMARY CONCERN. NORTHEASTERN SOUTH
DAKOTA AND WEST CENTRAL MINNESOTA REMAIN IN A SLIGHT RISK FOR
SEVERE WEATHER THIS EVENING AND OVERNIGHT.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THUNDERSTORMS ARE POSSIBLE ON SUNDAY ACROSS NORTHEAST SOUTH DAKOTA
AND WEST CENTRAL MINNESOTA...ALTHOUGH THE THREAT FOR SEVERE
WEATHER LOOKS TO BE LOW. THUNDERSTORMS ARE POSSIBLE AGAIN ON
TUESDAY OVER THE EASTERN PORTION OF THE FORECAST AREA.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS ANTICIPATED THIS EVENING THROUGH LATE
TONIGHT ALONG AND EAST OF A LINE FROM MOUND CITY TO BLUNT TO GANN
VALLEY.

SDZ003-015-033-045-301630-
CORSON-DEWEY-STANLEY-JONES-
1119 AM CDT SAT SEP 29 2007 /1019 AM MDT SAT SEP 29 2007/

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

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORMS...POSSIBLY SEVERE...ARE EXPECTED LATE THIS AFTERNOON
INTO THIS EVENING ACROSS CENTRAL SOUTH DAKOTA. LARGE HAIL AND
DAMAGING WINDS ARE THE PRIMARY SEVERE WEATHER THREAT WITH ANY
THUNDERSTORMS THAT BECOME SEVERE. HOWEVER...WIND SHEAR IN THE
ATMOSPHERE WILL SUPPORT SUPERCELL THUNDERSTORMS THIS AFTERNOON AND
EVENING...WHICH INCLUDES THE POTENTIAL FOR AN ISOLATED TORNADO
THROUGH EARLY THIS EVENING. A SLIGHT RISK FOR SEVERE WEATHER
CONTINUES LATE THIS AFTERNOON AND THIS EVENING FOR CENTRAL SOUTH
DAKOTA.

THE GRASSLAND FIRE DANGER WILL REACH THE EXTREME CATEGORY THIS
AFTERNOON WEST OF THE MISSOURI RIVER. RH VALUES WILL FALL TO
15 TO 20 PERCENT. HOWEVER...WIND SPEEDS WILL DROP OFF TO AROUND 15
MPH THIS AFTERNOON...PRECLUDING THE NEED FOR A RED FLAG WARNING.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS ANTICIPATED LATE THIS AFTERNOON THROUGH LATE
EVENING FROM CORSON COUNTY SOUTH TO JONES COUNTY.

DORN