Flash Flooding and Hail in South Dakota, July 1, 2011

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
900 AM CDT FRI JUL 1 2011

.UPDATE...
MADE TWEAKS TO TODAY/S FORECAST TO ACOUNT FOR A SLIGHTLY SLOWER
FROPA AND ARRIVAL OF SHOWERS/THUNDERSTORMS. ALTHOUGH THE
PERSISTENT ACTIVITY TO THE WEST OF THE CWA HAS BEEN SLOW TO SHIFT
EASTWARD THIS MORNING...EXPECT AN ACCELARATION AND EASTWARD PUSH
OF THE CONVECTION TO BE NOTABLE BETWEEN 17Z AND 21Z...AS THE
SHORTWAVE OVER WESTERN NEBRASKA KICKS EAST-NORTHEAST ACROSS THE
AREA TODAY. CONTINUE TO ALLOCATE THE HIGHEST POPS /60 PERCENT/
BETWEEN THE HOURS OF 18Z AND 00Z. BY EARLY EVENING...MOST OF THE
ACTIVITY SHOULD BE CONFINED TO NORTHWEST IA AND SW MN. ALSO
TWEAKED WINDS AND TEMPERATURE TRENDS TO ACCOUNT FOR THE FROPA TIMING.

&&

.PREV DISCUSSION... /ISSUED 330 AM CDT FRI JUL 1 2011/

CURRENTLY...UPPER WAVE VERY EVIDENT ON WATER VAPOR IMAGERY WITH ITS
CENTER SPINNING NEAR CHEYENNE WY. AHEAD OF THE WAVE...SCATTERED
SHOWERS AND THUNDERSTORMS CONTINUE TO BE FOUND THROUGHOUT CENTRAL
AND WESTERN SD...AS WELL AS WESTERN NEB. THOSE AREAS ARE BEHIND THE
COLD FRONT WITH COOLER MID LEVEL TEMPERATURES. AHEAD OF THE FRONT
FOR MUCH OF OUR FORECAST AREA...700MB TEMPERATURES REMAIN AROUND
+16C...UNABLE TO SUPPORT CONVECTION EXCEPT IN THE FAR REACHES OF OUR
AREA. UPPER QG FORCING CONTINUES ITS TREND OF SHOWING THE SHORT WAVE
MOVING SQUARELY ACROSS OUR FORECAST AREA TODAY. FRONTAL TIMING
BETWEEN THE NAM AND GFS WERE VERY CLOSE. BUT AS MENTIONED IN THE
AVIATION DISCUSSION BELOW...WINDS HAVE SHIFTED TO THE WEST OR NW
ALREADY FROM I 29 AND WESTWARD DUE TO THE EARLIER CONVECTION
WHICH PASSED ACROSS OUR WESTERN ZONES. IT IS PROBLEMATIC WHETHER THE
WINDS WILL KICK AROUND TO THE SOUTH AGAIN OR NOT...AS THE REAL FRONT
IS IN CENTRAL SD. OR...WILL SOME OF THESE WINDS STAY WESTERLY UNTIL
THE UPPER SUPPORT ARRIVES. AT ANY RATE...THE COLD FRONT SHOULD BE
CLEAR OF OUR FORECAST AREA BY 00Z SATURDAY. CHANCES FOR RAIN TODAY
IS STILL LIKELY...MAINLY ALONG THE I 90 CORRIDOR AND POINTS
NORTHWARD. HOWEVER UPSTREAM PROFILES ARE RATHER DRY SO WE ARE LIKELY
NOT TO RECEIVE WIDESPREAD HEAVY AMOUNTS WITH THIS SYSTEM. THE
PRECIPITATION WILL BE CONFINED PRIMARILY TO ALONG AND BEHIND THE
FRONT WHERE MID LEVEL TEMPERATURES ARE COOLER. WITH THE ANTICIPATED
SURFACE FRONTAL TIMING JUXTAPOSED NICELY WITH THE UPPER SUPPORT...
THERE WILL BE A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
ALONG AND EAST OF A SIOUX CITY TO WINDOM MINNESOTA LINE. CONCERNING
TEMPERATURES...READINGS REALLY WILL NOT MOVE MUCH FOR SOME OF OUR
NORTHERN ZONES...BUT ARE ANTICIPATED TO REACH THE MID 90S AGAIN
AROUND STORM LAKE AND SIOUX CITY.

ASIDE FROM EVENING THUNDERSTORMS FROM I 29 AND EASTWARD...THE REST
OF THE TONIGHT PERIOD LOOKS QUIET AS THE SHORT WAVE PASSES QUICKLY
EASTWARD. AFTER 00Z SATURDAY...THE ONLY LINGERING SEVERE WEATHER
THREAT WILL PROBABLY BE IN OUR FAR SOUTHEASTERN ZONES. FOR SATURDAY
WE ARE STILL LOOKING AT SEASONAL TEMPERATURES AS A SURFACE RIDGE OF
HIGH PRESSURE MOVES ACROSS THE I 29 CORRIDOR.

SATURDAY NIGHT AND SUNDAY MORNING STILL LOOK RATHER INTERESTING. THE
COLD FRONT THAT PASSES THROUGH TODAY GETS BOTTLED UP BETWEEN I 80
AND I 70 TO OUR SOUTH...THE USUAL FRONTAL GRAVEYARD FOR THIS TIME OF
YEAR. HOWEVER THE GFS AND ECMWF...AND EVEN THE NAM/GEM GLOBAL TO A
CERTAIN DEGREE...SHOW A STRONG SHORT WAVE MOVING EASTWARD ACROSS OUR
FORECAST AREA TO THE NORTH OF THE AFOREMENTIONED SURFACE STATIONARY
FRONT. LOW LEVEL MOISTURE PICKS UP AGAIN AS THE SURFACE RIDGE NUDGES
EASTWARD...SO CANNOT RULE OUT ELEVATED THUNDERSTORMS...ESPECIALLY
ACROSS THE SW HALF OF OUR AREA. THIS ACTIVITY THEN MOVES EASTWARD
SUNDAY MORNING ALONG THE MO RIVER AND I 29 CORRIDORS...BEFORE WANING
SUNDAY AFTERNOON. WITH A GOOD CHANCE OF CONVECTION FIRING UP ALONG
THE SURFACE FRONT TO OUR SOUTH...IT IS PROBLEMATIC WHETHER ANY
STORMS WILL HAVE ANY WIDESPREAD HEAVY RAINFALL IN OUR FORECAST AREA.
SO WITH THAT MUCH UNCERTAINTY...WILL LEAVE THE MENTION OF HEAVY RAIN
OUT OF THE FORTHCOMING HWO...ALSO NOTING THAT THE LOW LEVEL JET/
MOISTURE TRANSPORT VECTORS ARE NOT OVERLY STRONG.

TEMPERATURES WILL CONTINUE TO BE SEASONAL ON SUNDAY. THEN THE NEXT
WAVE AFFECTS OUR AREA LATE SUNDAY NIGHT. THE GFS BEGAN TO SHOW THIS
FEATURE YESTERDAY...AND NOW THE ECMWF HAS PICKED UP ON IT. THERE IS
AN 850MB FRONT WITH STRONG BAROCLINICITY STACKED UP RIGHT ACROSS OUR
FORECAST AREA. AS THE WAVE DIVES SOUTHEASTWARD DOWN THE EAST SIDE OF
THE UPPER RIDGE...THERE APPEARS TO BE ENOUGH INTERACTION BETWEEN THE
TWO FEATURES TO SPARK SOME THUNDERSTORMS MAINLY ALONG AND EAST OF
THE I 29 CORRIDOR. WEST OF I 29...THE ATMOSPHERE MAY BE A BIT CAPPED
OFF WITH 700MB TEMPERATURES PROGGED TO BE AROUND +12C IN THE JAMES
VALLEY. SO LEFT ANY MENTION OF PRECIPITATION OUT OF OUR WESTERN
ZONES FOR NOW. HUMIDITY RETURNS AGAIN EARLY NEXT WEEK. BUT THEN
A COLD FRONT LIKELY MOVING ACROSS THIS AREA LATE MONDAY NIGHT AND
TUESDAY SPARKING MORE CHANCES FOR RAINFALL...AND QUIETING THE
HUMIDITY LEVELS DOWN ON WEDNESDAY.

&&

.AVIATION.../ISSUED 330 AM CDT FRI JUL 1 2011/
GENERALLY VFR CONDITIONS EXPECTED THROUGH 02/12Z. EXCEPTIONS WOULD
BE IN THE FORM OF SCATTERED TSRA WITH AND BEHIND COLD FRONT. FRONT
SEEMS TO HAVE BEEN IN EFFECT FORCED EAST OVER CENTRAL PART OF AREA
AND NEAR FSD WHERE IT WILL PROBABLY STAY UNTIL UPPER SUPPORT CATCHES
UP WITH IT. THUNDERSTORMS ARE NOT EXPECTED TO PRODUCE MORE THAN VERY
LOCALIZED AND BRIEF MVFR CEILINGS AND VISIBILITIES MAINLY EASTERN
TWO THIRDS OF AREA BUT MAY PRODUCE LOCAL SURFACE GUSTS ABOVE 25
KNOTS. FRONT AND ANY THUNDERSTORMS SHOULD MOVE SOUTHEAST OF AREA BY
02/06Z. / WILLIAMS

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
MN...NONE.
NE...NONE.
SD...NONE.
&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1042 AM CDT FRI JUL 01 2011

SDZ038>040-050-052>071-MNZ071-072-080-081-089-090-097-098-
IAZ001>003-012>014-020>022-031-032-NEZ013-014-021200-
AURORA-BEADLE-BON HOMME-BROOKINGS-BRULE-BUENA VISTA IA-
CHARLES MIX-CHEROKEE IA-CLAY-CLAY IA-COTTONWOOD MN-DAKOTA NE-
DAVISON-DICKINSON IA-DIXON NE-DOUGLAS-GREGORY-HANSON-HUTCHINSON-
IDA IA-JACKSON MN-JERAULD-KINGSBURY-LAKE-LINCOLN-LINCOLN MN-
LYON IA-LYON MN-MCCOOK-MINER-MINNEHAHA-MOODY-MURRAY MN-NOBLES MN-
OBRIEN IA-OSCEOLA IA-PIPESTONE MN-PLYMOUTH IA-ROCK MN-SANBORN-
SIOUX IA-TURNER-UNION-WOODBURY IA-YANKTON-
1042 AM CDT FRI JUL 01 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST SOUTH DAKOTA...
SOUTHWEST MINNESOTA...NORTHWEST IOWA...AND NORTHEAST NEBRASKA.

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORMS...
SCATTERED SEVERE THUNDERSTORMS WILL BECOME POSSIBLE THROUGHOUT
THE DAY. A BROKEN LINE OF THUNDERSTORMS WILL PRODUCE ISOLATED
SEVERE THUNDERSTORMS IN CENTRAL SOUTH DAKOTA THROUGH EARLY
AFTERNOON WITH THE MAIN THREATS WIND GUSTS TO 60 MPH AND HAIL TO
THE SIZE OF QUARTERS. BY MID AFTERNOON STRONGER THUNDERSTORMS
WILL BE POSSIBLE EAST OF THE JAMES RIVER VALLEY WHERE HAIL TO THE
SIZE OF GOLF BALLS AND WIND GUSTS TO 70 MPH WILL BE POSSIBLE. THE
MAIN THREAT SHOULD OCCUR BEFORE 800 PM CDT.

FLOODING...
THE JAMES RIVER WILL BE IN FLOOD UNTIL FURTHER NOTICE.
ELSEWHERE...PARTS OF THE BIG SIOUX...LITTLE SIOUX...AND DES
MOINES RIVERS REMAIN IN FLOOD. BUT MANY PORTIONS OF THESE RIVERS
WILL FALL BELOW FLOOD STAGE THIS WEEKEND AND NEXT WEEK IF NO
HEAVY RAIN IS RECEIVED.

RECORD HIGH RELEASES ALONG THE MISSOURI RIVER WILL CONTINUE INTO
MID SUMMER. HIGH WATER LEVELS WILL CAUSE SIGNIFICANT IMPACTS
BETWEEN CHAMBERLAIN AND SIOUX CITY.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE IS A CHANCE OF THUNDERSTORMS ACROSS THE AREA SATURDAY NIGHT
AND SUNDAY MORNING BUT THESE THUNDERSTORMS ARE NOT EXPECTED TO
BECOME SEVERE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL BE POSSIBLE AFTER 100 PM CDT.

&&

FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE AT
WWW.WEATHER.GOV/SIOUXFALLS. THIS INCLUDES THE GRAPHICAL HAZARDOUS
WEATHER OUTLOOK.