040  
FGUS73 KFSD 231854  
ESFFSD  
SDC005-011-027-035-061-067-079-083-087-099-101-111-125-127-135-  
MNC033-063-081-083-101-105-117-133-NEC043-051-  
IAC021-035-041-059-093-119-141-143-149-167-193-221800-  
 
PROBABILISTIC HYDROLOGIC OUTLOOK  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
152 PM CDT THU SEP 23 2021  
 
IN TABLE 1 BELOW...THE CURRENT (CS) AND HISTORICAL (HS) OR NORMAL  
PROBABILITIES OF EXCEEDING MINOR...MODERATE...AND MAJOR FLOOD STAGES  
ARE LISTED FOR THE VALID TIME PERIOD.  
 
CS VALUES INDICATE THE PROBABILITY OF REACHING A FLOOD CATEGORY  
BASED ON CURRENT CONDITIONS.  
 
HS VALUES INDICATE THE PROBABILITY OF REACHING A FLOOD CATEGORY  
BASED ON HISTORICAL OR NORMAL CONDITIONS.  
 
WHEN THE VALUE OF CS IS MORE THAN HS...THE PROBABILITY OF  
EXCEEDING THAT LEVEL IS HIGHER THAN NORMAL. WHEN THE VALUE OF CS IS  
LESS THAN HS...THE PROBABILITY OF EXCEEDING THAT LEVEL IS LOWER  
THAN NORMAL.  
 
   
..TABLE 1--PROBABILITIES FOR MINOR...MODERATE AND MAJOR FLOODING
 
 
VALID PERIOD: 09/25/2021 - 12/24/2021  
 
: CURRENT AND HISTORICAL  
: CHANCES OF EXCEEDING  
: FLOOD CATEGORIES  
: AS A PERCENTAGE (%)  
CATEGORICAL :  
FLOOD STAGES (FT) : MINOR MODERATE MAJOR  
LOCATION MINOR MOD MAJOR : CS HS CS HS CS HS  
-------- ----- ----- ----- : --- --- --- --- --- ---  
:FLOYD RIVER  
SHELDON 12.0 14.0 16.0 : <5 <5 <5 <5 <5 <5  
ALTON 12.0 16.0 18.0 : <5 <5 <5 <5 <5 <5  
LE MARS 20.0 21.0 24.0 : <5 <5 <5 <5 <5 <5  
:WEST BRANCH FLOYD RIVER  
STRUBLE 14.0 15.0 16.0 : <5 <5 <5 <5 <5 <5  
:FLOYD RIVER  
MERRILL 12.0 14.0 16.0 : <5 <5 <5 <5 <5 <5  
JAMES 26.0 30.0 34.0 : <5 <5 <5 <5 <5 <5  
:LITTLE SIOUX RIVER  
MILFORD 12.0 14.0 16.0 : <5 22 <5 12 <5 7  
SPENCER 10.0 14.0 16.0 : <5 14 <5 <5 <5 <5  
:OCHEYEDAN RIVER  
SPENCER 8.0 9.5 10.5 : <5 <5 <5 <5 <5 <5  
:LITTLE SIOUX RIVER  
LINN GROVE 18.0 19.5 21.0 : <5 <5 <5 <5 <5 <5  
CHEROKEE 17.0 21.0 24.0 : <5 <5 <5 <5 <5 <5  
CORRECTIONVILLE 19.0 21.0 23.0 : <5 <5 <5 <5 <5 <5  
:WEST FORK DITCH  
HORNICK 20.0 22.0 26.5 : <5 <5 <5 <5 <5 <5  
:PERRY CREEK  
SIOUX CITY 24.0 26.0 28.0 : <5 <5 <5 <5 <5 <5  
:BIG SIOUX RIVER  
BROOKINGS 9.0 10.5 12.0 : <5 11 <5 8 <5 6  
DELL RAPIDS 12.0 14.0 15.0 : <5 7 <5 5 <5 <5  
SIOUX FALLS I-90 12.0 15.0 17.0 : <5 7 <5 5 <5 <5  
:SKUNK CREEK  
SIOUX FALLS 11.5 15.0 17.0 : <5 <5 <5 <5 <5 <5  
:BIG SIOUX RIVER  
SIOUX FALLS N CLIFF 16.0 18.0 31.0 : <5 6 <5 5 <5 <5  
:SPLIT ROCK CREEK  
CORSON 8.5 11.0 14.0 : <5 5 <5 <5 <5 <5  
:ROCK RIVER  
LUVERNE 10.0 12.0 14.0 : <5 <5 <5 <5 <5 <5  
ROCK RAPIDS 13.0 16.0 19.0 : 5 7 <5 <5 <5 <5  
ROCK VALLEY 16.0 17.0 19.0 : <5 <5 <5 <5 <5 <5  
:BIG SIOUX RIVER  
HAWARDEN 20.5 24.0 27.0 : 5 12 <5 6 <5 5  
AKRON 16.0 18.0 20.0 : 9 14 <5 7 <5 5  
SIOUX CITY 32.0 38.0 41.0 : <5 <5 <5 <5 <5 <5  
:JAMES RIVER  
HURON 11.0 13.0 15.0 : 5 7 <5 <5 <5 <5  
FORESTBURG 12.0 14.0 16.0 : <5 6 <5 <5 <5 <5  
MITCHELL 17.0 20.0 22.0 : <5 7 <5 <5 <5 <5  
:FIRESTEEL CREEK  
MOUNT VERNON 8.0 13.0 15.0 : <5 <5 <5 <5 <5 <5  
:JAMES RIVER  
SCOTLAND 13.0 14.0 16.0 : <5 <5 <5 <5 <5 <5  
YANKTON 12.0 14.0 16.0 : <5 <5 <5 <5 <5 <5  
:WEST FORK VERMILLION RIVER  
PARKER 9.0 10.0 11.0 : <5 <5 <5 <5 <5 <5  
:EAST FORK VERMILLION RIVER  
PARKER 12.0 14.0 16.0 : <5 5 <5 <5 <5 <5  
:VERMILLION RIVER  
DAVIS 11.0 13.0 15.0 : <5 10 <5 <5 <5 <5  
WAKONDA 14.0 15.5 17.0 : <5 10 <5 7 <5 6  
VERMILLION 21.0 22.0 30.0 : <5 <5 <5 <5 <5 <5  
:REDWOOD RIVER  
MARSHALL 14.0 15.0 16.5 : <5 <5 <5 <5 <5 <5  
:WEST FORK DES MOINES RIVER  
AVOCA 1425.0 1426.0 1428.0 : <5 <5 <5 <5 <5 <5  
JACKSON 12.0 12.5 14.0 : <5 <5 <5 <5 <5 <5  
WINDOM 19.0 21.0 25.0 : <5 <5 <5 <5 <5 <5  
:MISSOURI RIVER  
SOUTH SIOUX CITY 30.0 33.0 36.0 : <5 <5 <5 <5 <5 <5  
 
LEGEND  
CS = CONDITIONAL SIMULATION (CURRENT OUTLOOK)  
HS = HISTORICAL SIMULATION  
FT = FEET  
 
IN TABLE 2 BELOW...THE 95 THROUGH 5 PERCENT COLUMNS INDICATE THE  
PROBABILITY OF EXCEEDING THE LISTED STAGE LEVELS (FT) FOR THE VALID  
TIME PERIOD.  
   
..TABLE 2--EXCEEDANCE PROBABILITIES
 
 
CHANCE OF EXCEEDING STAGES  
AT SPECIFIC LOCATIONS  
VALID PERIOD: 09/25/2021 - 12/24/2021  
LOCATION 95% 90% 75% 50% 25% 10% 5%  
-------- ------ ------ ------ ------ ------ ------ ------  
:FLOYD RIVER  
SHELDON 4.5 5.1 5.2 6.2 7.6 8.8 10.3  
ALTON 5.4 5.6 5.8 6.5 8.9 10.0 10.7  
LE MARS 8.9 9.3 9.7 11.4 13.9 15.7 16.6  
:WEST BRANCH FLOYD RIVER  
STRUBLE 3.6 3.7 3.9 5.1 7.0 8.6 9.1  
:FLOYD RIVER  
MERRILL 0.0 0.0 0.0 1.2 3.2 4.6 5.3  
JAMES 8.2 8.2 8.4 9.0 10.4 11.7 12.4  
:LITTLE SIOUX RIVER  
MILFORD 7.3 7.3 7.4 8.0 10.1 10.6 11.6  
SPENCER 4.5 4.5 4.5 5.3 7.5 8.4 8.7  
:OCHEYEDAN RIVER  
SPENCER 1.9 2.0 2.3 2.6 3.6 4.1 4.5  
:LITTLE SIOUX RIVER  
LINN GROVE 5.8 5.8 6.0 6.8 8.4 9.3 9.6  
CHEROKEE 8.1 8.1 8.1 8.4 9.8 10.6 10.9  
CORRECTIONVILLE 4.7 4.7 4.7 5.3 6.0 8.2 8.5  
:WEST FORK DITCH  
HORNICK 6.1 6.4 7.1 7.5 8.1 10.5 12.4  
:PERRY CREEK  
SIOUX CITY 7.1 7.2 7.4 7.6 8.0 8.6 9.1  
:BIG SIOUX RIVER  
BROOKINGS 2.5 2.5 2.6 3.1 5.3 7.0 7.9  
DELL RAPIDS 3.2 3.2 3.3 3.9 6.0 7.7 8.5  
SIOUX FALLS I-90 4.5 4.5 4.6 5.6 8.2 9.8 10.2  
:SKUNK CREEK  
SIOUX FALLS 3.2 3.3 3.4 3.8 5.2 6.8 7.4  
:BIG SIOUX RIVER  
SIOUX FALLS N CLIFF 5.9 5.9 6.0 6.7 8.3 9.8 11.0  
:SPLIT ROCK CREEK  
CORSON 1.9 1.9 1.9 2.3 3.6 4.6 4.9  
:ROCK RIVER  
LUVERNE 4.6 4.6 4.6 5.4 6.7 7.9 8.5  
ROCK RAPIDS 7.9 7.9 7.9 9.1 10.7 12.1 12.9  
ROCK VALLEY 5.4 5.4 5.4 7.0 9.7 11.8 12.8  
:BIG SIOUX RIVER  
HAWARDEN 12.2 12.2 12.2 13.6 16.6 19.7 20.4  
AKRON 6.2 6.2 6.2 7.4 11.8 15.9 16.4  
SIOUX CITY 11.7 11.7 11.7 11.8 14.7 17.8 18.3  
:JAMES RIVER  
HURON 9.2 9.2 9.2 9.2 9.3 9.8 11.1  
FORESTBURG 4.6 4.6 4.6 4.6 5.1 6.4 9.6  
MITCHELL 10.4 10.4 10.4 10.5 10.8 12.4 15.3  
:FIRESTEEL CREEK  
MOUNT VERNON 2.0 2.0 2.0 2.0 2.0 3.9 5.3  
:JAMES RIVER  
SCOTLAND 4.4 4.4 4.4 4.4 4.6 6.4 9.0  
YANKTON 3.7 3.7 3.7 3.7 3.9 5.3 6.7  
:WEST FORK VERMILLION RIVER  
PARKER 0.7 0.7 0.7 0.7 1.3 2.4 2.9  
:EAST FORK VERMILLION RIVER  
PARKER 4.2 4.2 4.2 4.2 4.7 7.8 9.1  
:VERMILLION RIVER  
DAVIS 2.5 2.5 2.5 2.5 3.6 8.2 9.8  
WAKONDA 2.9 3.0 3.0 3.5 5.3 9.8 12.4  
VERMILLION 1.8 1.8 1.8 1.9 4.2 8.8 11.4  
:REDWOOD RIVER  
MARSHALL 7.4 7.4 7.4 7.7 9.1 9.9 10.6  
:WEST FORK DES MOINES RIVER  
AVOCA 1419.1 1419.1 1419.1 1419.1 1419.6 1421.0 1423.3  
JACKSON 8.1 8.1 8.1 8.1 8.8 9.8 10.0  
WINDOM 11.3 11.3 11.3 11.3 12.2 14.0 14.9  
:MISSOURI RIVER  
SOUTH SIOUX CITY 12.0 12.3 13.0 13.1 13.6 14.4 15.8  
 
IN TABLE 3 BELOW...THE 95 THROUGH 5 PERCENT COLUMNS INDICATE THE  
PROBABILITY OF FALLING BELOW THE LISTED STAGE LEVELS (FT) FOR THE  
VALID TIME PERIOD.  
   
..TABLE 3--NONEXCEEDANCE PROBABILITIES
 
 
CHANCE OF FALLING BELOW STAGES  
AT SPECIFIC LOCATIONS  
VALID PERIOD: 09/25/2021 - 12/24/2021  
LOCATION 95% 90% 75% 50% 25% 10% 5%  
-------- ------ ------ ------ ------ ------ ------ ------  
:FLOYD RIVER  
SHELDON 4.2 4.1 4.1 4.0 4.0 4.0 4.0  
ALTON 5.2 5.2 5.1 5.1 5.0 5.0 5.0  
LE MARS 7.5 7.5 7.3 7.1 6.9 6.9 6.9  
:WEST BRANCH FLOYD RIVER  
STRUBLE 3.4 3.4 3.4 3.3 3.3 3.3 3.3  
:FLOYD RIVER  
MERRILL 0.0 0.0 0.0 0.0 0.0 0.0 0.0  
JAMES 8.1 8.1 8.1 8.1 8.1 8.1 8.1  
:LITTLE SIOUX RIVER  
MILFORD 7.1 7.1 6.8 6.4 6.1 6.0 6.0  
SPENCER 3.7 3.6 3.5 3.4 3.2 3.2 3.2  
:OCHEYEDAN RIVER  
SPENCER 1.6 1.5 1.5 1.4 1.3 1.3 1.3  
:LITTLE SIOUX RIVER  
LINN GROVE 5.1 5.0 5.0 4.4 4.0 3.8 3.8  
CHEROKEE 6.6 6.3 6.2 5.6 5.1 5.0 5.0  
CORRECTIONVILLE 4.5 4.5 4.5 4.4 4.3 4.3 4.3  
:WEST FORK DITCH  
HORNICK 5.7 5.6 5.5 5.2 5.1 5.0 5.0  
:PERRY CREEK  
SIOUX CITY 5.0 5.0 5.0 5.0 5.0 5.0 5.0  
:BIG SIOUX RIVER  
BROOKINGS 2.4 2.3 2.2 1.9 1.7 1.6 1.6  
DELL RAPIDS 3.2 3.1 3.0 3.0 3.0 3.0 3.0  
SIOUX FALLS I-90 4.4 4.3 3.9 3.5 3.3 3.3 3.3  
:SKUNK CREEK  
SIOUX FALLS 2.5 2.5 2.4 2.3 2.2 2.2 2.2  
:BIG SIOUX RIVER  
SIOUX FALLS N CLIFF 5.9 5.8 5.7 5.5 5.4 5.3 5.3  
:SPLIT ROCK CREEK  
CORSON 1.8 1.8 1.7 1.6 1.5 1.5 1.5  
:ROCK RIVER  
LUVERNE 4.5 4.4 4.3 4.2 4.2 4.2 4.2  
ROCK RAPIDS 7.6 7.3 7.2 7.0 6.9 6.9 6.9  
ROCK VALLEY 5.3 5.2 5.0 4.6 4.4 4.4 4.4  
:BIG SIOUX RIVER  
HAWARDEN 11.9 11.8 11.1 10.2 10.0 10.0 10.0  
AKRON 5.4 5.3 4.5 3.9 3.5 3.5 3.5  
SIOUX CITY 10.4 10.4 9.8 9.2 9.0 9.0 9.0  
:JAMES RIVER  
HURON 9.1 9.1 9.1 9.1 9.0 9.0 9.0  
FORESTBURG 4.2 4.2 4.2 4.2 4.2 4.1 4.1  
MITCHELL 9.6 9.6 9.6 9.6 9.6 9.6 9.6  
:FIRESTEEL CREEK  
MOUNT VERNON 2.0 2.0 2.0 2.0 2.0 2.0 2.0  
:JAMES RIVER  
SCOTLAND 4.0 4.0 4.0 3.8 3.8 3.8 3.7  
YANKTON 3.5 3.5 3.5 3.5 3.5 3.5 3.5  
:WEST FORK VERMILLION RIVER  
PARKER 0.5 0.5 0.5 0.3 0.3 0.3 0.3  
:EAST FORK VERMILLION RIVER  
PARKER 4.0 3.6 3.5 3.4 3.4 3.4 3.4  
:VERMILLION RIVER  
DAVIS 2.4 2.4 2.4 2.4 2.4 2.4 2.4  
WAKONDA 1.7 1.5 1.4 1.1 1.0 1.0 1.0  
VERMILLION 1.2 1.2 1.2 1.2 1.2 1.2 1.2  
:REDWOOD RIVER  
MARSHALL 7.2 7.0 6.9 6.8 6.8 6.8 6.8  
:WEST FORK DES MOINES RIVER  
AVOCA 1418.8 1418.8 1418.4 1418.3 1418.2 1418.2 1418.2  
JACKSON 7.8 7.7 7.4 7.1 7.1 7.1 7.1  
WINDOM 11.1 10.8 10.6 10.4 10.4 10.4 10.4  
:MISSOURI RIVER  
SOUTH SIOUX CITY 7.8 7.6 7.0 6.5 6.1 5.9 5.5  
 
THESE LONG-RANGE PROBABILISTIC OUTLOOKS CONTAIN FORECAST VALUES THAT  
ARE CALCULATED USING MULTIPLE SEASON SCENARIOS FROM 30 OR MORE YEARS  
OF CLIMATOLOGICAL DATA...INCLUDING CURRENT CONDITIONS OF THE  
RIVER...SOIL MOISTURE...SNOW COVER...AND 30 TO 90 DAY LONG-RANGE  
OUTLOOKS OF TEMPERATURE AND PRECIPITATION. BY PROVIDING A RANGE OF  
PROBABILITIES...THE LEVEL OF RISK ASSOCIATED WITH LONG-RANGE PLANNING  
DECISIONS CAN BE DETERMINED. THESE PROBABILISTIC FORECASTS ARE PART  
OF THE NATIONAL WEATHER SERVICE'S ADVANCED HYDROLOGIC PREDICTION  
SERVICE.  
 
VISIT OUR WEB SITE WEATHER.GOV/FSD FOR MORE WEATHER AND WATER  
INFORMATION.  
 
THE NEXT OUTLOOK WILL BE ISSUED AROUND OCTOBER 28.  
 

 
 
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