Flash Flooding in South Dakota, August 17 to 18, 2007

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ABERDEEN SD
1051 PM CDT FRI AUG 17 2007

.UPDATE...
MADE SOME ADDITIONAL ADJUSTMENTS TO THE POP GRIDS/WORDED FORECAST
FOR TONIGHT...TO INCREASE TO 60 TO 80 PERCENT POPS OVER MUCH OF
THE FORECAST AREA...AS AREAL COVERAGE OF RETURNS IS BEGINNING TO
INCREASE SUBSTANTIALLY ACROSS CENTRAL SOUTH DAKOTA WHERE THE STRONGEST
MID-LEVEL LIFT/WAA HAS SET UP IN ASSOCIATION WITH APPROACHING
MID-LEVEL SHORTWAVE TROF. PRECIPITATION SHOULD SPREAD SLOWLY
EASTWARD ACROSS THE REST OF THE FORECAST AREA THROUGH THE
REMAINDER OF THE NIGHT AND INTO SATURDAY MORNING. UPDATED PUBLIC
PRODUCTS AND GRIDS FORTHCOMING.

&&
.PREV DISCUSSION...
.SHORT TERM...TONIGHT THROUGH MONDAY AFTERNOON
THE FOCUS OF THE SHORT TERM IS ON THE CHANCES AND TYPE OF
CONVECTION TONIGHT ACROSS THIS AREA. CURRENT WSR-88D SHOWS AN AREA
OF ONGOING CONVECTION IN NORTH CENTRAL AND NORTHEAST SOUTH DAKOTA.
THIS AREA HAS PRODUCED SOME SEVERE HAIL NEAR THE MISSOURI RIVER.
THE BACK EDGE OF THIS AREA IS NOTED NEAR THE MISSOURI RIVER ATTM.
THIS AREA WILL CONTINUE TO WEAKEN AS IT MOVES EAST. MORNING
SOUNDING FROM KABR SHOWS A VERY STABLE COLUMN ALOFT WITH NEAR
MOIST ADIABATIC LAPSE RATES. SOUNDINGS FROM KUNR SHOW A MORE
UNSTABLE MID LAYER. BUF KIT MODEL SOUNDINGS SHOW THIS UNSTABLE MID
LEVEL MOVING EAST TONIGHT AS UPPER LEVEL TROUGH COOLS MID LEVELS
SOME. SURFACE PLOTS AND VISIBLE SATELLITE DEPICT A PLUME OF LOW
CLOUDS AND HIGH DEW POINTS MOVING NORTH OUT OF NEBRASKA AND INTO
ONGOING CONVECTION. LATEST WATER VAPOR SATELLITE LOOP SHOWS
DEEPENING UPPER LEVEL H5 WAVE NOW MOVING INTO MONTANA. GFS
SUGGESTS TWO SEPARATE AREAS OF CONVECTION FORMING THIS EVENING.
ONE WOULD BE ASSOCIATED WITH THE H5 LOW CENTER OVER NORTH DAKOTA
AND A SECOND AREA FORMING IN RESPONSE TO A 40+ KNOT LOW LEVEL JET
THAT SETS UP THIS EVENING . THESE AREAS WOULD CONSOLIDATE IN
CENTRAL OR WESTERN SOUTH DAKOTA BY AROUND 06Z. BEST DYNAMICS
INCLUDING GOOD SHEAR VALUES WILL MOSTLY BE IN THE WESTERN PART OF
THE STATE. EXPECT THUNDERSTORMS THAT MOVE EAST TONIGHT WILL BE
LARGELY RAIN MAKERS WITH SOME THREAT OF HAIL AND WIND. SATURDAY
WILL SEE THE END OF THE CONVECTIVE AREA MOVING EAST OF THE REGION.
THE AREA WILL BE SLOW TO CLEAR AS A DISTURBED FLOW ALOFT IS NOTED
THROUGH MUCH OF THE DAY SATURDAY. SUNDAY WILL SEE THE LEE SIDE
SURFACE TROUGH START TO MOVE EAST AND WILL HAVE AN OLD BAROCLINIC
ZONE LYING NORTH SOUTH THROUGH WESTERN SOUTH DAKOTA TO HELP FOCUS
CONVECTION.

.LONG TERM...MONDAY NIGHT THROUGH FRIDAY
THE LONG TERM BEGINS WITH THE DEPARTURE OF THE UPPER RIDGE...WHICH
HAS DOMINATED THE UPPER LEVEL FLOW PATTERN THE LAST SEVERAL
DAYS. AN UPPER TROF IS PROGGED TO PASS OVER THE UPPER PLAINS
MONDAY INTO TUESDAY...FOLLOWED BY WESTERLY ZONAL FLOW FOR MOST OF
THE REST OF THE PERIOD. THE BEST CHANCES FOR PCPN LOOK TO BE
MONDAY...WITH THE PASSAGE OF A LOW PRESSURE SYSTEM AND ASSOCIATED
FRONTS. THIS SYSTEM IS ALSO SUPPORTED IN THE UPPER LEVELS BY THE
PREVIOUSLY MENTIONED UPPER TROF. TEMPERATURES STILL LOOK TO COOL SOMEWHAT
BY THE MIDDLE TO LATE IN THE WEEK...AS COOLER AND DRIER AIR PUSHES
IN BEHIND THE FRONT.

&&

.AVIATION...
SEVERAL FLIES IN THE OINTMENT WITH THIS 00Z TAF PACKAGE.

FIRST...HIGH LEVEL OF CONFIDENCE THAT ALL FOUR TAF TERMINALS WILL
SEE SHOWER AND/OR THUNDERSTORM ACTIVITY OVERNIGHT...STARTING FIRST
AT KPIR AND KMBG THIS EVENING...AND THEN SPREADING EAST IMPACTING
KABR AND KATY MUCH LATER IN THE NIGHT...AT OR AFTER 06Z. TIMING
THE DEVELOPMENT AND MOVEMENT OF CONVECTION STILL PROVING TO BE A
BIT OF A CHALLENGE...SO DID NOT GET CARRIED AWAY WITH -TSRA
MENTION...AND WILL FINE TUNE VCTS FORECAST AS THE STORMS FORM AND
BECOME A LITTLE BIT EASIER TO TRACK/TIME.

THE OTHER CHALLENGE IS STRATUS CLOUD DEVELOPMENT TONIGHT. ALL DAY
TODAY...LOW STRATUS CLOUDS WERE IN PLACE ACROSS PORTIONS OF
WESTERN AND CENTRAL SOUTH DAKOTA WHERE THE GREATEST AMOUNT OF LOW
LEVEL MOISTURE HAD MOVED TO. TONIGHT...ALL THE LOW LEVEL MOISTURE
POSITIONED ACROSS CENTRAL AND EASTERN NEBRASKA WILL MOVE NORTHWARD
AND WORK TO DEVELOP A LOW STRATUS CLOUD DECK WHICH IS EXPECTED TO
IMPACT ALL FOUR TERMINALS WITH SOME FORM OF EITHER MVFR /1000 TO
3000FT AGL/ CIGS OR IFR /LESS THAN 1000FT AGL/ CIGS AT OR AFTER
06Z TONIGHT AND STICK AROUND FOR A BETTER PART OF THE DAY ON
SATURDAY. AMENDMENTS WILL FOLLOW ACCORDINGLY AS THIS LOW CEILING
EVENT DEVELOPS/EVOLVES OVERNIGHT.

&&

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

UPDATE...DORN
SHORT TERM...KEEFE
LONG TERM...GIONTA
AVIATION...DORN

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE ABERDEEN SD
536 PM CDT FRI AUG 17 2007

MNZ039-046-SDZ006>008-011-019>023-182245-
TRAVERSE-BIG STONE-BROWN-MARSHALL-ROBERTS-DAY-CLARK-CODINGTON-
GRANT-HAMLIN-DEUEL-
536 PM CDT FRI AUG 17 2007

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

.DAY ONE...TONIGHT

CHANCES OF THUNDERSTORMS WILL BE ON THE INCREASE LATE THIS
EVENING...AND BECOMING LIKELY AFTER MIDNIGHT TONIGHT. THESE
STORMS ARE NOT EXPECTED TO BE SEVERE AT THIS TIME...HOWEVER...HEAVY
RAINFALL AND DANGEROUS LIGHTNING WILL BE POSSIBLE WITH THESE
THUNDERSTORMS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THUNDERSTORMS SHOULD BE ONGOING ON SATURDAY MORNING ACROSS THE
AREA...WITH CHANCES THROUGH THE EARLY AFTERNOON. THUNDERSTORMS ARE
AGAIN POSSIBLE MONDAY THROUGH WEDNESDAY...BUT IT IS TOO EARLY TO
DETERMINE MORE DEFINITE TIME PERIODS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED THIS EVENING...ALTHOUGH ANY
REPORTS OF LARGE HAIL OBSERVED OVERNIGHT WOULD BE GREATLY
APPRECIATED.

SDZ003>005-009-010-015>018-034>037-051-182245-
CORSON-CAMPBELL-MCPHERSON-WALWORTH-EDMUNDS-DEWEY-POTTER-FAULK-
SPINK-SULLY-HUGHES-HYDE-HAND-BUFFALO-
536 PM CDT FRI AUG 17 2007 /436 PM MDT FRI AUG 17 2007/

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

.DAY ONE...TODAY AND TONIGHT

CHANCES OF THUNDERSTORMS WILL INCREASE THIS EVENING...BECOMING
LIKELY BY LATE THIS EVENING INTO TONIGHT. THERE IS A SLIGHT CHANCE
THAT SOME OF THESE STORMS COULD BECOME SEVERE EARLY THIS EVENING
INTO TONIGHT WITH LARGE HAIL AND DAMAGING WINDS THE PRIMARY
HAZARDS. HEAVY RAINFALL WILL ALSO BE POSSIBLE WITH THESE
THUNDERSTORMS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE IS A CHANCE OF ONGOING THUNDERSTORMS SATURDAY MORNING.
THUNDERSTORMS ARE AGAIN POSSIBLE MONDAY THROUGH WEDNESDAY...BUT IT
IS TOO EARLY TO DETERMINE MORE DEFINITE TIME PERIODS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NECESSARY THIS EVENING THROUGH TONIGHT.

SDZ033-045-048-182245-
STANLEY-JONES-LYMAN-
536 PM CDT FRI AUG 17 2007 /436 PM MDT FRI AUG 17 2007/

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

.DAY ONE...TODAY AND TONIGHT

A TORNADO WATCH IS IN EFFECT UNTIL 1 AM CDT...12 AM MDT. CHANCES
OF THUNDERSTORMS WILL INCREASE THIS EVENING INTO TONIGHT. SOME OF
THESE STORMS COULD BECOME SEVERE THIS EVENING INTO TONIGHT WITH
LARGE HAIL...DAMAGING WINDS AND POSSIBLY A TORNADO OR TWO BEING
THE PRIMARY HAZARDS. HEAVY RAINFALL WILL ALSO BE POSSIBLE WITH
THESE THUNDERSTORMS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THUNDERSTORMS ARE POSSIBLE MONDAY THROUGH WEDNESDAY...BUT IT IS
TOO EARLY TO DETERMINE MORE DEFINITE TIME PERIODS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS BEING REQUESTED FOR THIS EVENING THROUGH
TONIGHT.

DORN