Severe Thunderstorm Warning 209, NWS Aberdeen, SD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ABERDEEN SD
536 AM CDT THU SEP 20 2007

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT
FORECAST CHALLENGES INCLUDE PRECIPITATION CHANCES TODAY INTO EARLY
THIS EVENING...ALONG WITH TEMPERATURES.

PRESENTLY SURFACE LOW PRESSURE IS DEEPENING IN A LEE OF THE
ROCKIES SURFACE TROF OVER THE WESTERN DAKOTAS. A WARM FRONT IS
ALSO DEVELOPING AND SLOWLY WORKING NORTHWARD INTO THE FORECAST
AREA. THUNDERSTORMS HAVE DEVELOPED OFF AND ON SINCE LATE LAST
EVENING...AND SEVERAL THUNDERSTORMS EARLY THIS MORNING HAVE
STRENGTHENED TO SEVERE LEVELS WITH LARGE HAIL THE PRIMARY CONCERN.
PLENTIFUL LOW LEVEL MOISTURE IS NOTED SURGING NORTHWARD INTO THE
FORECAST AREA AS DEWPOINTS ARE RISING RAPIDLY THROUGH THE 50S AT
THIS TIME.

WITH TWO DISTINCT JET MAXIMA EXPECTED TO LINK ARMS TODAY AND
ENHANCE UPPER LEVEL DIVERGENCE/LIFT NEEDED FOR FURTHER CONVECTIVE
DEVELOPMENT...HAVE CONTINUED WITH THE WX/POPS MENTION OF SHOWERS
AND THUNDERSTORMS...WITH THE HIGHEST CONCENTRATION OF POPS OVER
THE EASTERN FORECAST ZONES TODAY WHERE THE BEST
LIFT/FORCING/MOISTURE ADVECTION WILL BE ONGOING TODAY. THERE
REMAINS THE POTENTIAL FOR TORNADIC SUPERCELL THUNDERSTORM
DEVELOPMENT ALONG THIS SUBTLE WARM FRONTAL BOUNDARY FEATURE AS
WELL AS ANY OF THE OUTFLOW BOUNDARIES STILL LAYING AROUND THIS
AFTERNOON FROM THE CONVECTION THIS MORNING. THE SHEAR AND
INSTABILITY PROFILES CERTAINLY SUPPORT LARGE HAIL AND ISOLATED
TORNADOES TODAY INTO THIS EVENING ACROSS THE FAR EASTERN FORECAST
ZONES. THE THREAT FOR SUCH THUNDERSTORMS DEPENDS ON THE DEGREE OF
WARM UP TODAY AS SCT-BKN LOW CLOUDS ARE EVIDENT ON THE REGIONAL
SATELLITE PICS THIS MORNING...MOVING NORTH INTO THIS FORECAST
AREA.

EVEN WITH STORM SPEEDS OF 35 TO 50 MPH THIS MORNING...MANY AREAS
HAVE RECEIVED RADAR ESTIMATES OF 1 TO 2 INCHES OF RAINFALL WITH
LOCALLY HIGHER AMOUNTS. IF ANOTHER ROUND OF STORMS FORM LATER THIS
AFTERNOON/EVENING...FLASH FLOODING POTENTIAL WOULD CERTAINLY BE A
BIT HIGHER THAN IT HAS BEEN THIS MORNING. THE BEST LIFT/FORCING
ALL LOOKS TO PUSH EAST OF THIS AREA BY MIDNIGHT TONIGHT. ASIDE
FROM A BRIEF PERIOD OF MID-LEVEL LIFT...LATE TONIGHT/EARLY
FRIDAY...DIRECTLY ASSOCIATED WITH A POTENT UPPER LOW MOVING ALONG
THE INTERNATIONAL BORDER TONIGHT INTO FRIDAY...THE FORECAST AREA
SHOULD REMAIN DRY WITH HIGH PRESSURE AT THE SURFACE AND ALOFT
RESUMING DOMINANCE OF THE WEATHER PATTERN OVER THIS FORECAST AREA.

WAA SEQUENCE HAS BEGUN AND WILL CONTINUE INTO THE TONIGHT PERIOD
BEFORE A STRONG COLD FRONT BLASTS THROUGH THE FORECAST AREA FROM
NORTHWEST TO SOUTHEAST. THE DEGREE OF WARMING TODAY WILL BE A
FUNCTION OF LOW LEVEL CLOUDINESS WHICH IS CONTINUING TO STREAM
NORTH INTO THE STATE THIS MORNING. THE COLD FRONT SHOULD BE CLEAR
OF THE FORECAST AREA BY 15Z FRIDAY. REMARKABLE PERIOD OF CAA
FOLLOWS ON THE HEELS OF THE COLD FROPA...AND EXPECTING WINDS TO BE
PUSHING WIND ADVISORY CRITERIA LATE THURSDAY NIGHT THROUGH MID-DAY
ON FRIDAY. TRENDED TEMPERATURES DOWN ON FRIDAY SUBSTANTIALLY GIVEN
THE DEGREE OF COOLING EXPECTED /925HPA TEMPS TOPPING OUT AROUND
15C/.

.LONG TERM...SATURDAY THROUGH WEDNESDAY
MAIN FORECAST CHALLENGE IS PRECIPITATION CHANCES SUNDAY AND
MONDAY. EARLY SATURDAY...A LARGE UPPER LEVEL CUTOFF LOW WILL BE OVER
CALIFORNIA WITH A TROUGH PUSHING ONTO THE WEST COAST OF
CANADA...AND A RIDGE WILL BE OVER THE SOUTHERN AND SOUTHEASTERN
UNITED STATES. THE CUTOFF LOW WILL MERGE WITH THE NORTHWEST TROUGH
DURING THE DAY SATURDAY AND BECOMES ONE LARGE TROUGH WEST OF THE
ROCKIES. THE HIGH BUILDS OVER THE EAST...WITH SOUTHWEST FLOW
SETTING UP OVER THE PLAINS. THE WESTERN TROUGH SLIDES EAST TO
BECOME CENTERED OVER THE ROCKIES SUNDAY...WITH A SHORTWAVE SLIDING
ACROSS THE CWA SUNDAY NIGHT. THE TROUGH WEAKENS AND PUSHES ACROSS THE
PLAINS MONDAY...WITH WEAK TO MODERATE PVA REMAINING OVER EASTERN
SOUTH DAKOTA. THE TROUGH CONTINUES EAST ON TUESDAY WITH NEARLY
ZONAL TO SLIGHTLY NORTHWEST FLOW OVER THE UPPER MIDWEST...AND WEAK
RIDGING SLIDING OVER THE AREA WEDNESDAY.

AT THE SURFACE...HIGH PRESSURE WILL BE SOUTH AND EAST OF THE
REGION EARLY SATURDAY...WITH A TROUGH OVER EASTERN MONTANA. THE
HIGH PUSHES EAST AND THE LOW INTENSIFIES AND TRACKS TO WESTERN
NORTH DAKOTA...WITH A TROUGH OVER THE WESTERN HIGH PLAINS. THIS
SYSTEM PUSHES EAST ON SUNDAY WITH THE COLD FRONT REACHING THE
WESTERN CWA SUNDAY EVENING...AND MOVING THROUGH THE REST OF THE
CWA BY MORNING. THE FRONT CONTINUES EAST ON MONDAY...THEN HIGH
PRESSURE SLIDES OVER THE PLAINS MONDAY NIGHT AND REMAINS THE
DOMINANT FEATURE THROUGH THE END OF THE PERIOD. WILL KEEP A SLIGHT
CHANCE TO CHANCE POP GOING SUNDAY THROUGH THE DAY MONDAY WITH THE
FRONT MOVING THROUGH...THEN DRY FROM MONDAY NIGHT ON.

TEMPERATURES ON SATURDAY AND SUNDAY LOOK TO BE ABOVE NORMAL AS
DECENT WAA WILL BE IN PLACE AHEAD OF THE APPROACHING FRONT. ONCE
THE FRONT MOVES THROUGH...H85 TEMPS QUICKLY FALL FROM THE UPPER
TEENS INTO THE SINGLE DIGITS...AND DO NOT LOOK TO RECOVER UNTIL
POSSIBLY THE VERY END OF THE PERIOD. THEREFORE...LOOKING AT HIGHS
IN THE 80S SATURDAY AND SUNDAY...THEN ONLY IN THE MID 60S TO LOWER
70S MONDAY THROUGH WEDNESDAY.

&&

.AVIATION...
SCATTERED THUNDERSTORMS WILL TRACK ACROSS THE CENTRAL AND EASTERN
CWA THIS MORNING. CIGS AND VSBYS MAY FALL INTO THE IFR CATEGORY
UNDER THE STRONGER STORMS...WITH HAIL ALSO POSSIBLE. THE WESTERN
HALF OF THE CWA WILL SEE A SCT-BKN DECK OF CLOUDS AROUND 5K FEET
PUSH THROUGH DURING THE MORNING. THE AFTERNOON WILL SEE THE CHANCE
OF THUNDERSTORMS CONTINUE ACROSS THE EASTERN HALF OF THE
CWA...WITH A GOOD CHANCE FOR SEVERE STORMS ACROSS NORTHEAST
CWA...MAINLY AFFECTING K8D3.

&

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

SHORT TERM...DORN
LONG TERM...PARKIN
AVIATION...PARKIN

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE ABERDEEN SD
550 AM CDT THU SEP 20 2007

MNZ039-046-SDZ003>011-015>023-033>037-045-048-051-211100-
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-
550 AM CDT THU SEP 20 2007 /450 AM MDT THU SEP 20 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...POSSIBLY SEVERE...ARE EXPECTED TODAY INTO THIS
EVENING. THE GREATEST THREAT FOR SEVERE WEATHER WILL COME ALONG
AND EAST OF A LINE FROM GANN VALLEY TO LEOLA...WITH LARGE
HAIL...DAMAGING THUNDERSTORM WIND GUSTS AND PERHAPS EVEN A TORNADO
OR TWO ALL POSSIBLE TYPES OF SEVERE WEATHER TODAY. PAY CLOSE
ATTENTION TO THE UNFOLDING WEATHER CONDITIONS TODAY...AS HAZARDOUS
WEATHER COULD DEVELOP RATHER QUICKLY.

ONE OTHER CONCERN THIS AFTERNOON...FLASH FLOODING POTENTIAL.
THUNDERSTORMS THIS MORNING HAVE PUT DOWN A RATHER LARGE BLANKET OF
HEAVY RAINFALL ACROSS THE EASTERN PORTION OF THE FORECAST
AREA...AND ANY ADDITIONAL HEAVY RAINFALL THIS AFTERNOON OR THIS
EVENING MAY MAKE FLASH FLOODING A LITTLE EASIER TO COME BY.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THUNDERSTORMS ARE POSSIBLE AGAIN SUNDAY THROUGH MONDAY.

.SPOTTER INFORMATION STATEMENT...

DORN

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