061  
FGUS73 KUNR 132116  
ESFUNR  
SDC007-019-033-047-055-063-071-081-093-095-102-103-105-121-123-137-  
WYC005-011-045-270000-  
 
PROBABILISTIC HYDROLOGIC OUTLOOK  
NATIONAL WEATHER SERVICE RAPID CITY SD  
215 PM MST THU FEB 13 2020  
   
.SPRING FLOOD AND WATER RESOURCE OUTLOOK
 
 
...ABOVE AVERAGE FLOOD POTENTIAL THIS SPRING FOR PARTS OF WESTERN  
SOUTH DAKOTA...  
 
THIS SPRING FLOOD AND WATER RESOURCE OUTLOOK IS FOR THE RAPID CITY  
HYDROLOGIC SERVICE AREA (HSA), WHICH COVERS NORTHEASTERN WYOMING AND  
WESTERN SOUTH DAKOTA. THE MAIN RIVER BASINS INCLUDE THE LITTLE  
MISSOURI, EASTERN POWDER, BELLE FOURCHE, GRAND, MOREAU, CHEYENNE,  
BAD, WHITE, AND KEYAPAHA RIVER BASINS.  
   
FLOOD OUTLOOK SUMMARY
 
 
AT THIS TIME, THE PROBABILITY OF SPRING FLOODING THROUGH JUNE IS  
ABOVE AVERAGE, DUE TO SATURATED SOIL CONDITIONS AND HIGH RIVER  
LEVELS IN PARTS OF THE CHEYENNE RIVER, WHITE RIVER, BAD RIVER, LOWER  
GRAND AND LOWER MOREAU RIVER BASINS. THE POTENTIAL FOR ICE JAM  
RELATED FLOODING WILL REMAIN HIGH UNTIL THE ICE IS OFF OF THE  
RIVERS, STREAMS AND LAKES. DUE TO THE WARMER THAN AVERAGE  
TEMPERATURES THIS WINTER, THE ICE THICKNESS IS BELOW AVERAGE.  
THEREFORE, THE DURATION AND EXTENT OF ANY ICE JAM FLOODING THAT MAY  
OCCUR IS NOT EXPECTED TO BE AS BAD AS LAST YEAR.  
 
FOR THE BLACK HILLS AND HIGHER ELEVATIONS, FLOODING FROM SNOWMELT  
TYPICALLY BEGINS IN LATE APRIL AND MAY. FLOODING ON THE PLAINS DUE  
TO SNOWMELT AND ICE JAMS TYPICALLY OCCURS BETWEEN FEBRUARY AND MAY.  
THE POTENTIAL FOR RAINFALL-INDUCED FLASH FLOODING IS NOT  
QUANTIFIABLE BECAUSE THIS TYPE OF FLOODING IS USUALLY CAUSED BY  
LOCALIZED THUNDERSTORMS DURING THE SPRING AND SUMMER.  
 
THE FLOOD POTENTIAL IS STILL VERY DEPENDENT ON WEATHER CONDITIONS  
THIS SPRING. THE AMOUNT OF ADDITIONAL SNOW AND RAIN, AS WELL AS THE  
TIMING OF PEAK RIVER AND STREAM FLOWS, WILL HAVE A SIGNIFICANT  
EFFECT ON THE SEVERITY OF FLOODING.  
   
TEMPERATURES AND PRECIPITATION
 
 
SINCE OCTOBER 1 2019, TEMPERATURES HAVE BEEN BELOW AVERAGE AND  
PRECIPITATION HAS VARIED FROM BELOW AVERAGE ACROSS NORTHWESTERN  
SOUTH DAKOTA AND NORTHEASTERN WYOMING, TO ABOVE AVERAGE IN THE BLACK  
HILLS AND THE REST OF WESTERN SOUTH DAKOTA.  
 
HOWEVER, THE BELOW AVERAGE TEMPERATURES ARE SKEWED DUE TO THE VERY  
COLD CONDITIONS IN OCTOBER AND NOVEMBER. THEREFORE, LOOKING BACK TO  
DECEMBER 1, TEMPERATURES HAVE BEEN ABOVE AVERAGE IN MOST LOCATIONS  
BY 3 TO 5 DEGREES.  
 
SO FAR IN FEBRUARY, TEMPERATURES HAVE BEEN SLIGHTLY ABOVE AVERAGE  
AND PRECIPITATION HAS MAINLY BEEN ABOVE AVERAGE WITH THE EXCEPTION OF  
SOUTH CENTRAL SOUTH DAKOTA, WHERE PRECIPITATION SO FAR THIS MONTH IS  
BELOW AVERAGE.  
   
SNOW COVER AND LIQUID WATER CONTENT
 
 
SNOW COVER ON THE PLAINS IS MINIMAL, WITH MOST LOCATIONS REPORTING  
LESS THAN TWO INCHES OF SNOW ON THE GROUND. HIGHER SNOW DEPTH  
AMOUNTS ARE FOUND CLOSER TO CENTRAL SOUTH DAKOTA AND THE MISSOURI  
RIVER, WHERE SNOW AMOUNTS ARE CLOSE TO A FOOT. SNOW DEPTHS IN THE  
BLACK HILLS AND THE BEAR LODGE MOUNTAINS ARE IN THE RANGE OF 1 TO 3  
FEET WITH THE LIQUID CONTENT OF THE SNOW RANGING FROM 3 TO 6 INCHES.  
 
THE HALFWAY POINT OF THE SNOW SEASON WAS FEBRUARY 1, BUT MARCH AND  
APRIL ARE TYPICALLY THE TWO SNOWIEST MONTHS, WHEN A THIRD OF THE  
SEASONAL SNOWFALL USUALLY HAPPENS.  
   
SOIL CONDITIONS AND FROST DEPTHS
 
 
SOIL MOISTURE IS ABOVE AVERAGE AT 99 PERCENT, INDICATING VERY WET  
CONDITIONS. HOWEVER THE AMOUNT OF FROST IN THE GROUND IS LESS THAN  
AVERAGE, WITH FROST DEPTH READINGS RANGING FROM LESS THAN A FOOT  
AROUND THE BLACK HILLS AREA TO 12 TO 18 INCHES OF FROST IN THE  
GROUND ACROSS THE PLAINS OF WESTERN AND CENTRAL SOUTH DAKOTA.  
   
LAKE AND RIVER CONDITIONS
 
 
ALMOST ALL LAKES IN THE BLACK HILLS ARE ICE COVERED, BUT SOME  
PRAIRIE PONDS HAVE ONLY HAVE MINIMAL ICE THICKNESS. DUE TO THE  
WARMER TEMPERATURES SO FAR THIS WINTER, THE ICE THICKNESS IS BELOW  
AVERAGE.  
   
WEATHER OUTLOOKS
 
 
WATER TEMPERATURES IN THE TROPICAL PACIFIC OCEAN CONTINUE TO BE  
SLIGHTLY ABOVE AVERAGE, INDICATING NEUTRAL EL NINO SOUTHERN  
OSCILLATION (ENSO) CONDITIONS. THE OUTLOOK INDICATES NEUTRAL  
CONDITIONS WILL CONTINUE THROUGH THE SPRING. THIS WEATHER PATTERN  
WILL TYPICALLY BRING WARMER CONDITIONS TO THE SOUTHERN AND WESTERN  
PARTS OF THE UNITED STATES, WITH WETTER CONDITIONS OVER THE CENTRAL  
PLAINS. FOR THE SUMMER, THE PREDICTABILITY IS LOW FOR ANY TYPE OF  
OVERALL WEATHER PATTERN.  
 
THE OUTLOOK FOR THE NEXT TWO WEEKS INDICATES A GREATER CHANCE FOR  
WARMER THAN AVERAGE TEMPERATURES WITH BELOW AVERAGE PRECIPITATION.  
 
THE THREE MONTH OUTLOOK FOR MARCH, APRIL, AND MAY CALLS FOR EQUAL  
CHANCES FOR ABOVE, BELOW, OR NEAR AVERAGE TEMPERATURES WITH A  
GREATER CHANCE FOR ABOVE AVERAGE PRECIPITATION.  
   
NUMERICAL RIVER OUTLOOKS
 
 
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: 02/15/2020 - 09/30/2020  
 
: 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  
-------- ----- ----- ----- : --- --- --- --- --- ---  
:LITTLE MISSOURI RIVER  
CAMP CROOK 12.0 17.0 19.0 : 47 33 18 12 <5 6  
:MOREAU RIVER  
FAITH 16.0 18.0 21.0 : 10 12 5 <5 <5 <5  
:BELLE FOURCHE RIVER  
WY-SD STATE LINE 15.0 16.0 18.0 : 14 13 10 <5 <5 <5  
STURGIS 15.0 17.0 19.0 : 18 18 13 12 10 5  
ELM SPRINGS 19.0 22.0 24.0 : 12 8 9 <5 <5 <5  
:CHEYENNE RIVER  
WASTA 13.0 15.0 16.0 : <5 <5 <5 <5 <5 <5  
PLAINVIEW 17.0 19.0 20.0 : 58 28 26 21 21 11  
:BAD RIVER  
MIDLAND 21.0 24.0 25.0 : 35 27 <5 <5 <5 <5  
:WHITE RIVER  
KADOKA 15.0 16.0 19.0 : 59 33 48 26 15 8  
WHITE RIVER 14.0 15.0 17.0 : 57 37 44 30 19 10  
OACOMA 15.0 20.0 25.0 : 77 57 30 15 7 <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: 02/15/2020 - 09/30/2020  
LOCATION 95% 90% 75% 50% 25% 10% 5%  
-------- ------ ------ ------ ------ ------ ------ ------  
:LITTLE MISSOURI RIVER  
CAMP CROOK 3.7 5.4 7.4 11.1 14.8 18.2 18.6  
:MOREAU RIVER  
FAITH 5.2 5.4 7.8 10.3 13.9 15.9 18.5  
:BELLE FOURCHE RIVER  
WY-SD STATE LINE 4.7 5.1 6.3 8.3 11.1 16.0 16.5  
STURGIS 5.4 6.1 8.1 9.4 12.7 19.0 21.0  
ELM SPRINGS 7.0 7.5 9.4 11.9 13.8 20.8 23.4  
:CHEYENNE RIVER  
WASTA 3.2 3.7 5.0 7.1 9.3 11.2 12.1  
PLAINVIEW 12.5 13.2 14.9 17.2 19.3 22.2 23.1  
:BAD RIVER  
MIDLAND 5.7 6.6 12.2 18.5 22.3 22.6 22.7  
:WHITE RIVER  
KADOKA 7.5 8.2 10.7 15.8 18.0 19.4 19.8  
WHITE RIVER 7.8 8.4 10.6 14.8 16.6 17.9 19.6  
OACOMA 12.5 13.8 15.3 18.3 21.2 23.3 26.2  
 
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: 02/15/2020 - 09/30/2020  
LOCATION 95% 90% 75% 50% 25% 10% 5%  
-------- ------ ------ ------ ------ ------ ------ ------  
:LITTLE MISSOURI RIVER  
CAMP CROOK 2.0 2.0 2.0 1.7 1.4 1.4 1.4  
:MOREAU RIVER  
FAITH 0.8 0.8 0.8 0.7 0.6 0.6 0.5  
:BELLE FOURCHE RIVER  
WY-SD STATE LINE 3.3 3.2 3.2 3.1 3.0 3.0 3.0  
STURGIS 3.1 3.1 3.0 2.9 2.9 2.9 2.8  
ELM SPRINGS 4.4 4.3 4.3 4.2 4.2 4.1 4.1  
:CHEYENNE RIVER  
WASTA 0.7 0.6 0.6 0.5 0.5 0.4 0.4  
PLAINVIEW 8.5 8.5 8.5 8.5 8.5 8.5 8.5  
:BAD RIVER  
MIDLAND 3.5 3.5 3.4 3.4 3.3 3.3 3.3  
:WHITE RIVER  
KADOKA 4.6 4.5 4.3 4.0 4.0 4.0 4.0  
WHITE RIVER 3.7 3.6 3.4 2.8 2.7 2.7 2.7  
OACOMA 7.4 7.3 7.2 6.7 6.6 6.6 6.6  
 
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/UNR FOR MORE WEATHER AND WATER  
INFORMATION.  
 
THIS IS THE FIRST SCHEDULED SPRING FLOOD AND WATER RESOURCE OUTLOOK  
FOR 2020. LONG-RANGE PROBABILISTIC OUTLOOKS ARE ISSUED NEAR THE  
MIDDLE OF THE MONTH THROUGHOUT THE YEAR. THE NEXT SPRING FLOOD  
OUTLOOK WILL BE ISSUED ON FEBRUARY 27, 2020.  
 

 
 
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