HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE GREAT FALLS MT
608 PM MDT TUE APR 08 2008
...MONTANA WATER SUPPLY OUTLOOK AS OF APRIL 2008...
MONTANA WATER SUPPLY FORECAST ISSUED BY THE NATIONAL WEATHER SERVICE
OFFICE IN GREAT FALLS IN COOPERATION AND COORDINATION WITH THE
NATIONAL WEATHER SERVICE OFFICE IN MISSOULA AND THE NATURAL
RESOURCES CONSERVATION SERVICE...USDA.
THE WATER SUPPLY OUTLOOK FOR THE 2008 SUMMER SEASON PROJECTS WATER
SUPPLIES WEST OF THE CONTINENTAL DIVIDE TO BE NEAR AVERAGE WITH SOME
BASINS FORECAST TO BE ABOVE AVERAGE. EAST OF THE CONTINENTAL
DIVIDE...WATER SUPPLIES ARE FORECAST TO BE NEAR TO BELOW AVERAGE
WITH SOME AREAS IN CENTRAL AND NORTH CENTRAL MONTANA FORECAST TO BE
WELL BELOW AVERAGE. THESE FORECASTS ASSUME NEAR NORMAL MOISTURE AND
RUNOFF CONDITIONS FOR APRIL THROUGH JULY AND DO NOT ACCOUNT FOR
MUCH BELOW AVERAGE...70 PERCENT OR LESS...OR ABOVE AVERAGE...110
PERCENT OR MORE...SNOWMELT OR SPRING RAINS.
ON APRIL 1...THE MOUNTAIN SNOWFALL SEASON IS ABOUT 95 PERCENT
COMPLETE. THE MOUNTAINS WILL TYPICALLY REACH SEASONAL PEAKS DURING
APRIL. APRIL 1 SNOWPACK STATEWIDE WAS SLIGHTLY ABOVE AVERAGE AND
WELL ABOVE LAST YEAR. HOWEVER...THERE ARE SOME RIVER BASINS WITH
AREAS OF BELOW AVERAGE SNOWPACK THAT WILL NEED CLOSE MONITORING
INCLUDING THE JEFFERSON BASIN...THE UPPER CLARK FORK BASIN...THE
JUDITH BASIN...THE MUSSELSHELL BASIN AND THE UPPER YELLOWSTONE
BASIN.
WHILE A SERIES OF STORMS CROSSED MONTANA DURING MARCH BRINGING
SCATTERED PRECIPITATION...MOST AREAS ENDED THE MONTH WITH BELOW
NORMAL PRECIPITATION. ONE STORM MOVED THROUGH ON THE MARCH 4TH AND
5TH... BRINGING 8 TO 12 INCHES OF SNOW TO HIGHER ELEVATIONS IN THE
WEST AND 2 TO 6 INCHES TO LOWER ELEVATIONS. ACROSS THE EAST...2 TO 6
INCHES OF SNOW WAS COMMON ACROSS CENTRAL MONTANA. MARCH 21ST AND
22ND...A STORM BROUGHT 2 TO 6 INCHES OF SNOW TO WESTERN MONTANA.
THIS WAS THE START OF A STORMY PERIOD THAT LASTED THROUGH THE END OF
THE MONTH. NORTHEAST MONTANA PICKED UP 3 TO 6 INCHES OF SNOW ON THE
28TH. ON MARCH 29TH...ANOTHER STRONGER STORM SYSTEM MOVED ACROSS
MONTANA AND NORTHWEST MONTANA RECEIVED UP TO A FOOT OF SNOW WITH 6
INCHES COMMON NORTH CENTRAL. AS THIS SYSTEM MOVED THROUGH THE GREAT
FALLS AREA...BLIZZARD CONDITIONS PREVAILED FOR A LITTLE OVER TWO
HOURS. NOT MUCH SNOW FELL IN THE GREAT FALLS AREA...BUT 18 INCHES
FELL AROUND CLEVELAND AND A FOOT IN THE BEARS PAW MOUNTAINS.
IN THE MOUNTAINS...SEVERAL SNOTEL SITES IN THE NORTHERN
ROCKIES...NORTHWEST AND SOUTHWEST MONTANA REPORTED OVER 100 INCHES
OF SNOW ON THE GROUND AT THE END OF THE MONTH. SOIL MOISTURE
CONDITIONS EAST OF THE DIVIDE SHOWED AN INTERESTING TREND...SINCE
SOIL MOISTURE PROBES WERE INSTALLED AT GREAT FALLS IN 2003...THE
END-OF-MONTH VALUES IN MARCH 2008 WERE THE DRIEST OF RECORD FOR THE
DATE. THE PROBES ARE AT 6...12...18 AND 30 INCH DEPTHS.
SNOWPACK...
MOUNTAIN SNOWPACK AS OF APRIL 1...
PERCENT OF PERCENT OF
AVERAGE LAST YEAR
STATEWIDE 108 155
WEST OF THE CONTINENTAL DIVIDE 113 151
EAST OF THE CONTINENTAL DIVIDE 103 153
PRECIPITATION...
MOUNTAIN AND VALLEY PRECIPITATION AVERAGES FOR MARCH...
PERCENT OF PERCENT OF
AVERAGE LAST YEAR
STATEWIDE 81 113
WEST OF THE CONTINENTAL DIVIDE 92 114
EAST OF THE CONTINENTAL DIVIDE 74 112
MOUNTAIN AND VALLEY PRECIPITATION AVERAGES FOR THE WATER YEAR...
PERCENT OF PERCENT OF
AVERAGE LAST YEAR
STATEWIDE 99 98
WEST OF THE CONTINENTAL DIVIDE 102 97
EAST OF THE CONTINENTAL DIVIDE 97 99
CALENDAR YEAR AND WATER YEAR 2008 PERCENT OF NORMAL PRECIPITATION FOR
SELECTED CITIES ARE SHOWN BELOW...
PERCENT OF NORMAL PERCENT OF NORMAL
CALENDAR YEAR 2008 WATER YEAR 2008
CITY JAN 1 TO MAR 31 OCT 1 TO MAR 31
BILLINGS 33 78
BOZEMAN 51 91
BUTTE 56 71
CUT BANK 16 42
DILLON 77 136
GLASGOW 99 109
GREAT FALLS 74 72
HAVRE 61 47
HELENA 60 81
KALISPELL 61 65
LEWISTOWN 38 59
MILES CITY 7 17
MISSOULA 78 76
RESERVOIRS...
MAJOR RESERVOIR STORAGE AS OF APRIL 1
PERCENT OF PERCENT OF
AVERAGE LAST YEAR
STATEWIDE 81 95
WEST OF THE CONTINENTAL DIVIDE 139 88
EAST OF THE CONTINENTAL DIVIDE 66 99
PERCENT OF NORMAL RESERVOIR STORAGE AS OF APRIL 1 FOR SELECTED
RESERVOIRS
RESERVOIR PERCENT OF NORMAL
APRIL APRIL
2008 2007
BIGHORN RESERVOIR 99 96
CANYON FERRY RESERVOIR 98 109
CLARK CANYON RESERVOIR 78 85
FLATHEAD LAKE 82 122
FORT PECK LAKE 59 57
FRESNO RESERVOIR 58 143
GIBSON RESERVOIR 56 123
HEBGEN RESERVOIR 109 108
HUNGRY HORSE RESERVOIR 122 153
LAKE ELWELL / TIBER RESERVOIR 95 99
LAKE KOOCANUSA 154 153
LAKE SHERBURNE 116 145
LIMA RESERVOIR 55 126
NELSON RESERVOIR 90 97
PISHKIN RESERVOIR 47 94
SWIFT RESERVOIR 86 99
WILLOW CREEK RESERVOIR 111 133
STREAMFLOW...
BELOW ARE AVERAGED RIVER BASIN RUNOFF FORECAST SUMMARIES FOR THE
PERIOD APRIL THROUGH SEPTEMBER. THESE FORECASTS ASSUME NEAR NORMAL
SPRING CONDITIONS AND DO NOT ACCOUNT FOR WELL BELOW AVERAGE...70 OR
LESS...OR ABOVE AVERAGE...110 OR MORE...SNOWMELT OR SPRING RAIN.
FORECASTS FOR RIVERS AND SITES WEST OF THE CONTINENTAL DIVIDE ARE
PROVIDED BY THE NORTHWEST RIVER FORECAST CENTER IN
PORTLAND...OREGON. FORECASTS FOR RIVERS AND SITES EAST OF THE
CONTINENTAL DIVIDE ARE FROM THE MISSOURI BASIN RIVER FORECAST CENTER
IN PLEASANT HILL...MISSOURI. ALL FORECASTS ARE IN COOPERATION AND
COORDINATION WITH NATURAL RESOURCES CONSERVATION SERVICE...USDA.
MOST
PROBABLE REASONABLE REASONABLE
FORECAST MAXIMUM MINIMUM
PERIOD /PCT AVG/ /PCT AVG/ /PCT AVG/
COLUMBIA RIVER BASIN
KOOTENAI RIVER
LIBBY RESVR INFLOW APR-SEP 99 119 80
CLARK FORK
ABOVE BLACKFOOT RIVER APR-SEP 103 151 56
ABOVE MISSOULA APR-SEP 100 129 71
BELOW MISSOULA APR-SEP 107 130 83
ST. REGIS APR-SEP 109 137 82
NEAR PLAINS APR-SEP 105 126 84
BLACKFOOT RIVER
NEAR BONNER APR-SEP 98 130 66
BITTERROOT RIVER
AT MOUTH APR-SEP 114 135 93
NORTH FORK FLATHEAD RIVER
NEAR COLUMBIA FALLS APR-SEP 108 127 88
MIDDLE FORK FLATHEAD RIVER
NEAR WEST GLACIER APR-SEP 103 120 87
SOUTH FORK FLATHEAD RIVER
HUNGRY HORSE RES INFLOW APR-SEP 100 121 79
FLATHEAD RIVER
COLUMBIA FALLS APR-SEP 103 125 81
FLATHEAD LAKE INFLOW APR-SEP 103 123 82
SASKATCHEWAN RIVER BASIN
ST. MARY RIVER
BABB NR APR-SEP 99 114 83
MISSOURI RIVER BASIN
RED ROCK RIVER
LIMA RES INFLOW APR-SEP 99 142 56
BEAVERHEAD RIVER
CLARK CANYON INFLOW APR-SEP 101 173 48
BARRETTS APR-SEP 100 153 47
RUBY RIVER
RUBY RESERVOIR INFLOW APR-SEP 77 107 52
BIG HOLE RIVER
NEAR MELROSE APR-SEP 83 96 70
MADISON RIVER
HEBGEN RES INFLOW APR-SEP 109 127 93
ENNIS RESERVOIR INFLOW APR-SEP 101 119 82
GALLATIN RIVER
NEAR GALLATIN GATEWAY APR-SEP 103 123 83
LOGAN APR-SEP 104 138 71
MISSOURI RIVER
TOSTON APR-SEP 101 134 69
FORT BENTON APR-SEP 104 136 71
VIRGELLE APR-SEP 103 136 70
NEAR LANDUSKY APR-SEP 102 135 69
BELOW FORT PECK DAM APR-SEP 101 134 68
SHEEP CREEK
WHITE SULPHUR SPRINGS APR-SEP 92 130 60
SUN RIVER
GIBSON RES INFLOW APR-SEP 96 114 79
MARIAS RIVER
NEAR SHELBY APR-SEP 100 133 67
MUSSELSHELL RIVER
HARLOWTON APR-SEP 46 111 9
MILK RIVER
WESTERN CROSSING APR-SEP 94 167 43
MILK RIVER...AB APR-SEP 106 188 33
EASTERN CROSSING APR-SEP 93 170 25
YELLOWSTONE RIVER
YELLOWSTN LK OUTLT...WY APR-SEP 120 135 104
CORWIN SPRINGS APR-SEP 116 131 102
NEAR LIVINGSTON APR-SEP 116 132 100
BILLINGS APR-SEP 113 139 87
MILES CITY APR-SEP 109 135 83
NEAR SIDNEY APR-SEP 110 136 84
BOULDER RIVER
--More--(59%)
BIG TIMBER APR-SEP 103 127 79
STILLWATER RIVER
NEAR ABSAROKEE APR-SEP 101 121 80
CLARKS FORK YELLOWSTONE RIVER
NEAR BELFRY APR-SEP 122 134 109
LITTLE BIGHORN RIVER
NEAR HARDIN APR-SEP 94 129 58
TONGUE RIVER
TONGUE RIVER RES INFLOW APR-SEP 104 148 68
POWDER RIVER
MOORHEAD APR-SEP 113 176 64
LOCATE APR-SEP 115 171 60
DEFINITIONS
MOST PROBABLE FORECAST...GIVEN THE CURRENT HYDROMETEOROLOGICAL
CONDITIONS TO DATE...THIS IS THE BEST ESTIMATE OF WHAT THE ACTUAL
RUNOFF VOLUME
WILL BE THIS SEASON.
REASONABLE MAXIMUM FORECAST...GIVEN CURRENT HYDROMETEOROLOGICAL
CONDITIONS...THE SEASONAL RUNOFF THAT HAS A TEN (10) PERCENT
CHANCE OF BEING EXCEEDED.
REASONABLE MINIMUM FORECAST...GIVEN CURRENT HYDROMETEOROLOGICAL
CONDITIONS...THE SEASONAL RUNOFF THAT HAS A NINETY (90) PERCENT
CHANCE OF BEING EXCEEDED.
SURFACE WATER SUPPLY INDEX...
THE SURFACE WATER SUPPLY INDEX...SWSI...IS A MEASURE OF AVAILABLE
SURFACE WATER AVAILABILITY FOR THE SPRING AND SUMMER MONTHS. WATER
USERS WHO RELY ON MOUNTAIN PRECIPITATION CAN USE THE INDEX TO
EVALUATE SEASONAL SURFACE WATER SUPPLIES. THE SWSI ACCOUNTS FOR
MOUNTAIN SNOWPACK...MOUNTAIN PRECIPITATION...STREAMFLOW...RESERVOIR
STORAGE AND SOIL MOISTURE. SWSI VALUES ARE CALCULATED FOR 52 BASINS
IN MONTANA. SWSI VALUES ARE PROVIDED BY THE NATURAL RESOURCES
CONSERVATION SERVICE...USDA.
NUMBER OF BASINS
SWSI RATING SURFACE WATER CONDITION 2008 2007
-3.0 TO -4.0 EXTREMELY DRY 2 10
-2.0 TO -2.9 MODERATELY DRY 2 13
-1.0 TO -1.9 SLIGHTLY DRY 4 16
-0.9 TO +0.9 NEAR AVERAGE 24 10
+1.0 TO +1.9 SLIGHTLY WET 15 2
+2.0 TO +2.9 MODERATELY WET 4 2
+3.0 TO +4.0 EXTREMELY WET 0 0
NOT AVAILABLE 2 0
VALUES FOR SPECIFIC BASINS AS OF APRIL 1 2008 AND 2007 ARE LISTED
BELOW...
SWSI SWSI
BASIN 2008 2007
Tobacco River 1.5 -1.2
Kootenai Ft. Steele to Libby Dam 0.9 0.6
Kootenai River below Libby Dam 2.5 2.4
Fisher River 2.3 -2.0
Yaak River 1.6 1.2
North Fork Flathead River 1.2 0.5
Middle FORK Flathead River 1.3 -1.3
South Fork Flathead River 1.3 2.4
Flathead River at Columbia Falls 1.2 1.3
Swan River 0.1 -1.6
Flathead River at Polson 1.0 0.2
Mission Valley NA -1.9
Little Bitterroot River NA -3.0
Clark Fork River above Milltown 1.3 -1.2
Blackfoot River 0.3 -2.1
Bitterroot River 2.0 -2.1
Clark Fork River below Bitterroot River 1.7 -1.8
Clark Fork River below Flathead River 1.2 -0.5
Beaverhead River -0.2 -2.2
Ruby River -0.8 -4.0
Big Hole River 0.4 -1.7
Boulder River (Jefferson) -1.1 -1.9
Jefferson River 0.7 -1.6
Madison River 0.7 -2.2
Gallatin River 1.0 -3.2
Missouri River above Canyon Ferry 0.1 -2.1
Missouri River below Canyon Ferry -0.3 -3.0
Smith River 0.9 0.2
Sun River -0.3 -0.6
Teton River 0.6 -1.4
Birch/Dupuyer Creeks -2.9 -3.3
Upper Judith River -2.9 -3.1
Marias River above Tiber -0.2 -1.6
Marias River below Tiber -1.3 -2.4
Musselshell River -1.5 -2.4
Missouri River above Ft. Peck -0.8 -1.3
Missouri River below Ft. Peck -3.4 -4.0
St. Mary River 1.2 -0.9
Milk River -1.9 -0.5
Dearborn River near Craig 0.6 -1.7
Yellowstone River above Livingston 2.0 -2.4
Shields River -0.3 -3.2
Boulder River (Yellowstone) 0.7 -3.3
Stillwater River 0.6 -2.3
Rock/Red Lodge Creeks -3.2 -3.4
Clarks Fork River 2.5 -2.4
Yellowstone River above Bighorn River 1.7 -2.5
Bighorn River below Bighorn Lake 0.1 -1.9
Little Bighorn River 1.2 -1.5
Yellowstone River below Bighorn River 1.0 -2.2
Tongue River 2.7 0.2
Powder River 2.0 -1.7
OUTLOOK...
THE OUTLOOK FOR THE REMAINDER OF APRIL INDICATES THERE IS A 33 TO 50
PERCENT CHANCE TEMPERATURES WILL BE BELOW NORMAL OVER THE WESTERN
HALF OF MONTANA. FOR THE REMAINDER OF THE STATE...STATISTICAL TOOLS
SHOW NO TENDENCIES FOR THIS PERIOD...AND THE OUTLOOK CALLS FOR EQUAL
CHANCES OF ABOVE...BELOW OR NEAR NORMAL TEMPERATURES. FOR
PRECIPITATION...THERE IS A 33 TO 50 PERCENT CHANCE PRECIPITATION WILL
BE ABOVE NORMAL WEST OF THE DIVIDE. EAST OF THE DIVIDE...THERE IS A
33 TO 40 PERCENT CHANCE OF PRECIPITATION WILL BE ABOVE NORMAL ALONG
THE ROCKY MOUNTAIN FRONT AND ADJACENT PLAINS. FOR THE REMAINDER OF
THE STATE...STATISTICAL TOOLS SHOW NO TENDENCY FOR THIS FORECAST
PERIOD RESULTING IN A PRECIPITATION OUTLOOK OF EQUAL CHANCES FOR
ABOVE...BELOW OR NEAR NORMAL CONDITIONS.
FOR THE PERIOD MAY THROUGH JULY...STATISTICAL TOOLS SHOW THERE IS A
33 TO 40 PERCENT CHANCE FOR ABOVE NORMAL TEMPERATURES WEST OF THE
DIVIDE AS WELL AS OVER SOUTHWEST MONTANA AND THE WESTERN PORTION OF
SOUTH CENTRAL MONTANA. FOR THE REMAINDER OF THE STATE...STATISTICAL
TOOLS SHOW NO TENDENCIES FOR THIS PERIOD...AND THE OUTLOOK CALLS FOR
EQUAL CHANCES OF ABOVE...BELOW OR NEAR NORMAL TEMPERATURES. FOR
PRECIPITATION...THERE IS A 33 TO 40 PERCENT CHANCE PRECIPITATION
WILL BE BELOW NORMAL OVER THE WESTERN HALF OF MONTANA. FOR THE
EASTERN HALF OF THE STATE...STATISTICAL TOOLS SHOW NO
TENDENCIES...AND THE OUTLOOK CALLS FOR EQUAL CHANCES OF
ABOVE...BELOW OR NEAR NORMAL PRECIPITATION ACROSS THE STATE FOR THE
MAY THROUGH JULY PERIOD.
THE NEXT WATER SUPPLY OUTLOOK FOR 2008 WILL BE ISSUED BY MAY 15.
LOSS