HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE BOISE IDAHO
845 AM MDT TUES MAR 11 2008
...IDAHO SPRING FLOOD OUTLOOK AND WATER SUPPLY FORECAST...
DISCUSSION...
THE WETTER AND COLDER THAN NORMAL WEATHER PATTERN WHICH AFFECTED
IDAHO FROM MID DECEMBER THROUGH EARLY FEBRUARY CHANGED TO A DRIER
AND MILD WEATHER PATTERN IN MID FEBRUARY. SNOW DEPTHS AND SNOW
WATER EQUIVALENTS WHEN COMPARED TO NORMAL LEVELS ARE STILL ABOVE
NORMAL IN CENTRAL AND NORTHERN IDAHO ESPECIALLY BETWEEN 3000 FEET AND
5000 FEET ELEVATION. THESE ANOMALIES IN SNOW PACK AT LOW ELEVATIONS
ARE NOT AS GREAT AS THEY WERE 30 DAYS AGO BUT ARE STILL RESULTING IN
AN ABOVE AVERAGE THREAT OF SPRING FLOODING...PRIMARILY ON SMALL
STREAMS WITHIN THE WEISER...PAYETTE...AND CLEARWATER RIVER BASINS.
THE THREAT OF SMALL STREAM FLOODING IS ALSO ABOVE AVERAGE THIS SPRING
IN THE IDAHO PANHANDLE REGION. SNOW PACK IN OTHER AREAS OF THE STATE
INCLUDING MOST OF THE UPPER SNAKE RIVER BASIN AND ITS TRIBUTARIES IS
VERY CLOSE TO NORMAL FOR THIS TIME OF YEAR AND WILL RESULT IN AN
AVERAGE THREAT OF SPRING FLOODING IN 2008. WATER SUPPLIES WILL BE
MUCH BETTER THAN LAST YEAR WITH MOST STREAMS PRODUCING NEAR NORMAL
VOLUMES IN SOUTHERN IDAHO AND SLIGHTLY ABOVE NORMAL VOLUMES IN
CENTRAL AND NORTHERN IDAHO DURING THE APRIL THROUGH JULY TIME PERIOD.
SNOWPACK...
SNOWPACK OBSERVATIONS ON MARCH 10TH AT NRCS SNOTEL AND SNOW COURSE
LOCATIONS INDICATED THAT THE CENTRAL AND NORTHERN PORTION OF THE
STATE HAD ABOVE NORMAL SNOW PACK RANGING FROM 110 TO 120 PERCENT
OF NORMAL. SNOW TOTALS IN SOUTHERN IDAHO INCLUDING MOST OF THE
STREAM BASINS ON THE SOUTH SIDE OF THE SNAKE RIVER WERE NEAR AVERAGE
IN THE RANGE OF 95 TO 105 PERCENT OF NORMAL. ANOMALOUSLY HIGH SNOW
PACK AT LOW ELEVATIONS HAS DIMINISHED SLIGHTLY IN MOST AREAS OF THE
STATE. HOWEVER SNOW IN THE WEISER...PAYETTE...SALMON...AND CLEARWATER
BASINS IS STILL SIGNIFICANTLY ABOVE NORMAL IN THE 3000 TO 6000 FOOT
ELEVATION ZONE.
LONG RANGE TEMPERATURE AND PRECIPITATION FORECASTS...
SEA SURFACE TEMPERATURES IN THE TROPICAL PACIFIC ARE BELOW NORMAL
INDICATING LA-NINA CONDITIONS. WHILE LA-NINA PATTERNS GENERALLY
RESULT IN ABOVE NORMAL WINTER SNOWPACKS IN IDAHO DURING THE WINTER
MONTHS...IT IS NOT A GOOD PREDICTOR OF FUTURE WEATHER PATTERNS
DURING THE LATE SPRING MONTHS. THE OFFICIAL NWS CLIMATE PREDICTION
CENTER FORECAST FOR MARCH INDICATES AN INCREASED PROBABILITY OF
COOLER AND WETTER CONDITIONS THROUGH THE REST OF MARCH. THERE IS NO
PREFERENCE FOR EITHER WETTER OR DRYER THAN NORMAL CONDITIONS BEYOND
APRIL 1ST.
FLOOD POTENTIAL...
BASED ON CURRENT SNOWPACK AND SOIL MOISTURE CONDITIONS...THE THREAT
OF SNOW MELT RELATED FLOODING IN SPRING 2008 IS ABOVE AVERAGE IN
CENTRAL AND NORTHERN IDAHO. THIS PRIMARILY INCLUDES SMALLER STREAMS
WHICH DERIVE MOST OF THEIR FLOW FROM LOWER AND MID-ELEVATION SNOW
PACK. RIVER BASINS IN THE AREA OF ABOVE AVERAGE FLOOD THREAT
INCLUDE THE WEISER...NORTHERN PORTIONS OF THE PAYETTE...CLEARWATER...
AND STREAMS IN THE IDAHO PANHANDLE REGION. IN ADDITION...RUNOFF IN
AREAS THAT WERE BURNED BY WILDFIRES IN SUMMER 2007 WILL BE
SIGNIFICANTLY ENHANCED WITH INCREASED RISK OF DEBRIS FLOWS AND
MUDSLIDES. SIGNIFICANT PORTIONS OF THE PAYETTE...BIG WOOD AND SALMON
RIVER BASINS WERE BURNED IN 2007. THE GREATEST RISK OF DEBRIS FLOWS
WILL OCCUR NEAR THE END OF THE SNOW MELT SEASON IN APRIL OR MAY
ESPECIALLY WHEN RAINFALL OCCURS.
THE RISK OF FLOODING ON MOST LARGER STREAMS WHICH ARE REGULATED BY
DAMS AND RESERVOIRS IS AVERAGE AT THIS TIME. THIS IS BECAUSE HIGH
ELEVATION SNOWPACK IS ONLY SLIGHTLY ABOVE NORMAL AND MOST RESERVOIRS
HAVE SOME EXTRA SPACE AVAILABLE DUE TO DROUGHT CONDITIONS WHICH
OCCURRED IN 2007.
THE FOLLOWING TABLE LISTS AREAS WITH AN INCREASED RISK OF FLOODING
FROM DURING SPRING 2008...
RIVER...STREAM...AREA OF CONCERN DATES OF GREATEST CONCERN
WEISER RIVER IN ADAMS COUNTY LATE MARCH THROUGH
AND WASHINGTON COUNTY EARLY APRIL
CAMAS CREEK IN CAMAS COUNTY LATE MARCH THROUGH EARLY
MAY
SMALL STREAMS IN VALLEY COUNTY APRIL THROUGH EARLY MAY
INCLUDING GOLD FORK AND LAKE FORK
NEAR DONNELLY
SMALL STREAMS IN CLEARWATER COUNTY LATE MARCH THROUGH
MID APRIL
SMALL STREAMS IN IDAHO PANHANDLE APRIL THROUGH MAY
REGION
STREAMS IN IDAHO PANHANDLE LATE MARCH THROUGH MAY
REGION INCLUDING ST JOE...ST MARIES
PEAK SPRING FLOWS RESULTING FROM A NORMAL MELTING OF CURRENT AND
PROJECTED SEASONAL SNOWPACK ARE LISTED IN THE FOLLOWING TABLE.
LONG RANGE FORECASTS HAVE SOME MARGIN OF ERROR AND A REASONABLE
RANGE OF POSSIBLE VALUES IS LISTED FOR PLANNING PURPOSES. FORECAST
FLOWS BELOW RESERVOIRS REPRESENT NATURAL FLOW AND DO NOT ACCOUNT FOR
FLOOD CONTROL OPERATIONS WHICH WOULD MITIGATE THE PEAK TO SOME
DEGREE.
STREAM AND LOC. FLOOD STAGE FORECAST REASONABLE RANGE
SNAKE RIVER
HEISE ID 24500 CFS 21300 CFS 17100 - 25500 CFS
SHELLEY ID 25600 CFS 21200 CFS 16700 - 25700 CFS
TETON RIVER
ST ANTHONY ID 4750 CFS 4100 CFS 3100 - 5100 CFS
HENRYS FORK
ST ANTHONY ID 9000 CFS 8800 CFS 7700 - 10000 CFS
REXBURG ID 9.5 FEET 10.2 FEET 9.9 - 10.6 FEET
PORTNEUF RIVER
POCATELLO ID 1140 CFS 900 CFS 600 - 1200 CFS
BIG WOOD RIVER
HAILEY ID 4000 CFS 2800 CFS 2200 - 3500 CFS
BOISE RIVER
LUCKY PEAK INFLOW NONE 13800 CFS 11900 - 15700 CFS
BRUNEAU RIVER
HOT SPRINGS ID 3200 CFS 2200 CFS 1200 - 3200 CFS
PAYETTE RIVER
EMMETT ID 16000 CFS 13300 CFS 11700 - 14800 CFS
WEISER RIVER
WEISER ID 8900 CFS 7600 CFS 5900 - 9400 CFS
SELWAY RIVER
LOWELL ID 42300 CFS 39700 CFS 29425 - 46310 CFS
CLEARWATER RIVER
STITES ID 9600 CFS 7050 CFS 5650 - 8870 CFS
ORIFINO ID 75000 CFS 69800 CFS 60080 - 85840 CFS
MIDDLE FORK SALMON
MIDDLE FORK LODGE NONE 6.5 FEET 6.0 - 7.1 FEET
SALMON RIVER
SALMON 14000 CFS 8470 CFS 6480 - 12680 CFS
WHITE BIRD 99000 CFS 71400 CFS 60900 - 81900 CFS
COEURD ALENE RIVER
ENAVILLE 27000 CFS 13300 CFS 9800 - 23300 CFS
CATALDO 21350 CFS 16400 CFS 14400 - 19200 CFS
ST JOE RIVER
CALDER 25600 CFS 16500 CFS 13100 - 22200 CFS
ST MARIES 32.5 FEET 32.5 FEET 32.0 - 33.0 FEET
MALHEUR RIVER
VALE 9.5 FEET 7.8 FEET 5.7 - 9.9 FEET
VOLUME FORECASTS...
SEASONAL VOLUME FORECASTS COORDINATED BETWEEN THE NATIONAL WEATHER
SERVICE AND THE NATURAL RESOURCES CONSERVATION SERVICE ARE BASED ON
PRECIPITATION AND SNOWPACK OBSERVED UP UNTIL MARCH 1ST AND
ASSUME NORMAL PRECIPITATION WILL OCCUR DURING APRIL THROUGH JUNE.
THE VOLUME FORECASTS AND PERCENT OF AVERAGE FOR SELECTED STREAMS AND
LOCATIONS ARE LISTED BELOW. NOTE THAT THE VOLUMES ARE EXPRESSED
IN THOUSANDS OF ACRE FEET.
STREAM AND LOCATION STATE PERIOD VOL %AVE
SNAKE RIVER
JACKSON LAKE INFLOW WY APR-JUL 800 98
PALISADES RES INFLOW WY APR-JUL 3240 97
HEISE ID APR-JUL 3460 97
SHELLY ID APR-JUL 4560 103
BLACKFOOT ID APR-JUL 4590 100
AMER. FALLS RES IN ID APR-JUL 3140 97
KING HILL ID APR-JUL 2160 71
MURPHY ID APR-JUL 2270 73
WEISER ID APR-JUL 4900 85
BROWNLEE RES INFLOW ID APR-JUL 5500 87
HELLS CANYON ID APR-JUL 5660 87
HENRYS FORK
ASHTON ID APR-JUL 570 100
ST. ANTHONY ID APR-JUL 735 100
REXBURG ID APR-JUL 1520 97
TETON RIVER
ST. ANTHONY ID APR-JUL 410 102
BIG LOST RIVER
MACKAY RES INFLOW ID APR-JUL 138 97
WILLOW CREEK
RIRIE RES INFLOW ID APR-JUL 79 92
PORTNEUF RIVER
TOPAZ, ID ID APR-JUL 83 87
GOOSE CREEK
OAKLEY RES INFLOW ID APR-JUL 26 90
BIG WOOD RIVER
HAILEY ID APR-JUL 260 102
MAGIC RES INFLOW ID APR-JUL 290 100
LITTLE WOOD RIVER
CAREY ID APR-JUL 91 105
BRUNEAU RIVER
HOT SPRINGS ID APR-JUL 189 91
OWYHEE RIVER
OWYHEE RES INFLOW OR MAR-JUL 545 89
OWYHEE RES OUTFLOW OR APR-JUL 36 17
BOISE RIVER
TWIN SPRINGS ID APR-JUL 635 100
ANDERSON RNCH RES INF ID APR-JUL 540 100
BOISE ID APR-JUL 1400 99
PARMA ID APR-JUL 305 51
MALHEUR RIVER
DREWSEY OR MAR-JUL 118 107
BEULAH RES INFLOW OR MAR-JUL 87 107
PAYETTE RIVER
HORSESHOE BEND ID APR-JUL 1760 109
EMMETT ID APR-JUL 1580 127
N.F. PAYETTE RIVER
CASCADE RES INFLOW ID APR-JUL 550 111
DEADWOOD RIVER
DEADWOOD RES INFLOW ID APR-JUL 146 109
WEISER RIVER
WEISER ID APR-JUL 465 119
POWDER RIVER
SUMPTER OR MAR-JUL 76 109
SALMON RIVER
SALMON ID APR-JUL 870 102
WHITEBIRD ID APR-JUL 6150 105
CLEARWATER RIVER
ORIFINO ID APR-JUL 5120 110
SPALDING ID APR-JUL 8450 114
N.F CLEARWATER RIVER
DWORSHAK RES INFLOW ID APR-JUL 2920 110
PEND OREILLE RIVER
PEND OREILLE LAKE IN ID APR-JUL 12800 100
COEUR D ALENE RIVER
ENAVILLE ID APR-JUL 810 110
COEUR D ALENE LAKE IN ID APR-JUL 2800 110
ST JOE RIVER
CALDER ID APR-JUL 1250 110
THE IDAHO SPRING FLOOD OUTLOOK AND WATER SUPPLY FORECAST WILL UPDATED
ON OR BEFORE APRIL 11TH 2008.
BREIDENBACH