HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
130 PM MST THU FEB 24 2005
...SPRING 2005 RUNOFF VOLUME AND FLOOD OUTLOOK FOR WESTERN AND
CENTRAL WYOMING...
THE HYDROLOGICAL AREA IN THIS OUTLOOK INCLUDES THE WIND, BIG HORN,
GREEN, POWDER, SWEETWATER, SHOSHONE, AND UPPER YELLOWSTONE RIVER
BASINS. A SMALL PORTION OF THE SNAKE AND THE LOWER NORTH PLATTE
BASINS IS ALSO USED TO MAKE THIS RUNOFF FORECAST.
...LITTLE TO NO SPRING SNOWMELT FLOODING EXPECTED...
...ABOVE AVERAGE VOLUME FORECASTS FOR THE SWEETWATER DRAINAGE, NEAR
NORMAL STREAMFLOWS EXPECTED FOR THE GREEN RIVER BASIN, AND
BELOW NORMAL VOLUME FORECASTS FOR THE REST OF THE WATERSHEDS...
...MODERATE TO SEVERE HYDROLOGIC DROUGHT CONTINUES FOR WESTERN AND
SOUTHWESTERN WYOMING...EXTREME HYDROLOGIC DROUGHT FOR NORTH
CENTRAL WYOMING...
THE FORECAST PERIOD FOR THIS OUTLOOK IS FROM APRIL TO THE END
OF JULY. THIS OUTLOOK IS SCHEDULED TO BE UPDATED NEAR THE
MIDDLE OF MARCH.
**CURRENT HYDROLOGIC AND CLIMATOLOGICAL CONDITIONS**
CURRENT STREAMFLOWS...ALTHOUGH MANY RIVERS ARE FROZEN THIS TIME
OF THE YEAR, THE FEW THAT ARE NOT ARE REPORTING SHOW
SLIGHTLY ABOVE NORMAL FLOWS. THIS IS TO BE EXPECTED SINCE
WYOMING'S AVERAGE TEMPERATURES DURING PAST FEW WEEKS HAS BEEN
ABOVE NORMAL.
SNOWPACK...EARLY STORMS COVERED THE REGION WITH SNOW, BUT BELOW
AVERAGE SNOWFALL WAS RECORDED DURING LATE NOVEMBER THROUGH THE
MIDDLE OF FEBRUARY. SNOW WATER EQUIVALENTS (SWES) VARIED FROM
73 PERCENT OF AVERAGE IN THE NORTHWEST TO 100 TO 110 PERCENT
OF AVERAGE SWE OVER THE SOUTHWEST PART OF THE STATE. NOTABLY,
THE WIND, UPPER GREEN, AND LOWER GREEN WATERSHEDS HAVE HAD
ABOVE NORMAL SWES FOR THE ENTIRE WINTER.
PRECIPITATION....JANUARY PRECIPITATION VARIED FROM AS LOW AS 50
TO 65 OF AVERAGE OVER THE SNAKE, SHOSHONE, BIG HORN, AND POWDER
WATERSHEDS...TO 105 TO 125 PERCENT OF AVERAGE OVER THE WIND,
UPPER GREEN, AND LOWER GREEN DRAINAGES.
TEMPERATURES...OVERALL, TEMPERATURES HAVE BEEN ABOVE NORMAL FOR
ALL BASINS THROUGHOUT THE WINTER. FEBRUARY TEMPERATURES HAVE
BEEN WELL ABOVE AVERAGE FOR MANY DRAINAGES EAST OF THE
CONTINENTAL DIVIDE AND TEMPERATURES WERE NEAR NORMAL FOR
WATERSHEDS WEST OF THE DIVIDE.
SOIL MOISTURE...THERE HAS BEEN SOME NOTICEABLE IMPROVEMENT IN
THE OVERALL MOISTURE CAPACITY OF THE REGION'S WATERSHEDS, DUE
TO A COOLER THAN NORMAL/WETTER THAN NORMAL SUMMER AND FALL OF
2004. LIMITED SOIL MOISTURE DATA SHOW THAT NEAR NORMAL SOIL
MOISTURE CONDITIONS EXIST OVER THE SOUTHERN WATERSHEDS, AND
BELOW SOIL MOISTURE CONDITIONS OVER NORTHERN DRAINAGES.
RESERVOIR LEVELS....RESERVOIR STORAGE LEVELS CONTINUE TO BE
RATHER LOW. THE ONLY EXCEPTION IS BOYSEN RESERVOIR, WHICH HAS
SEEN A DRAMATIC JUMP FROM 55 PERCENT CAPACITY LAST FEBRUARY TO
NEAR 85 PERCENT CAPACITY THIS YEAR.
RESERVOIR %CAPACITY
BOYSEN 84
FONTENELLE 45
PATHFINDER 25
JACKSON LAKE 17
BUFFALO BILL 72
PILOT BUTTE 81
BULL LAKE 68
DROUGHT...MODERATE TO SEVERE HYDROLOGIC DROUGHT CONTINUES FOR
WESTERN AND SOUTHWESTERN WYOMING. NORTH CENTRAL WYOMING, WITHIN
THE LAST 4 TO 6 WEEKS, HAS BEEN DOWNGRADED TO THE EXTREME
HYDROLOGIC DROUGHT CATEGORY. LITTLE IMPROVEMENT IN THE
DROUGHT IS EXPECTED THROUGH MAY.
**CLIMATOLOGICAL/HYDROLOGICAL OUTLOOK AND FORECAST CONDITIONS**
CLIMATOLOGICAL OUTLOOK...
SHORT RANGE (NEXT 10 DAYS)...CENTRAL AND WESTERN WYOMING
WILL EXPERIENCE NEAR NORMAL PRECIPITATION AND TEMPERATURE
CONDITIONS.
LONG RANGE (MID MARCH-JUNE)...NEAR NORMAL PRECIPITATION
AND ABOVE NORMAL TEMPERATURES.
HYDROLOGICAL OUTLOOK...SNOW WATER EQUIVALENTS (SWES) FROM THE
MOUNTAIN SNOWPACK USUALLY PEAK AROUND LATE APRIL THROUGH EARLY
MAY IN WESTERN AND CENTRAL WYOMING. ALSO, 30 TO 50 PERCENT OF
THE TOTAL SWES USUALLY OCCUR IN MARCH THROUGH THE BEGINNING OF
MAY. PEAK FLOW MAGNITUDES ARE VERY DEPENDENT UPON LATE SPRING
TEMPERATURES AND THE ENSUING MELT SCENARIO THAT DEVELOPS. GIVEN
THE AMOUNT OF SNOWPACK ALREADY IN THE MOUNTAINS COUPLED WITH
THE CLIMATOLOGICAL PREDICTIONS FOR THE NEXT THREE MONTHS, SWE
PEAKS ARE NOT EXPECTED TO BE MUCH ABOVE NORMAL TO CAUSE
SIGNIFICANT RISES IN SNOWMELT RUNOFF AND STREAMFLOW VOLUMES.
THERE MUST A SIGNIFICANT WEATHER PATTERN CHANGE IN THE NEXT
60 DAYS TO DRASTICALLY INCREASE SNOWPACK NUMBERS TO WARRANT
CONCERN FOR SIGNIFICANT SNOWMELT RUINOFF.
FLOODING FROM SPRING RUNOFF WILL ALSO BE INHIBITED DUE TO
DECREASED DIRECT RUNOFF FROM CONTINUED DRY ANTECEDENT SOIL
MOISTURE CONDITIONS AS WELL AS DECREASED OUTFLOW RELEASES
FROM LOW RESERVOIRS. THERE MAY SOME SIGNIFICANT RISES ON SOME
SMALLER HEADWATER BASINS IF A RAIN-ON-SNOWPACK SCENARIO
DEVELOPS; HOWEVER, THE DRY CONDITIONS OF THE SOILS AND
VEGETATION WITHIN THESE SMALLER DRAINAGES WILL CAUSE
SIGNIFICANT INTERCEPTION, INFILTRATION, AND PERCOLATION OF
AVAILABLE WATER WHICH WILL GREATLY INHIBIT DIRECT RUNOFF AND
OVERLAND FLOW.
FORECAST CONDITIONS...
VOLUME...OVERALL, SPRING RUNOFF VOLUME FORECASTS ARE
EXPECTED TO BE BELOW NORMAL FOR THE MAJORITY OF THE
BASINS ACROSS THE WESTERN TWO-THIRDS OF WYOMING.
THE NOTICEABLE EXCEPTION IS THE SWEETWATER DRAINAGE,
WHERE STREAMFLOWS ARE EXPECTED WELL ABOVE NORMAL
THE FOLLOWING ARE THE PRELIMINARY STREAMFLOW VOLUME FORECASTS
FOR SELECTED LOCATIONS...ASSUMING NORMAL PRECIPITATION THROUGH THE
REST OF THE SEASON.
MOST PROBABLE FORECAST
VOLUME PERCENT
STREAM AND STATION PERIOD 1000 AF OF AVG
_______________________ ______ _______ _______
GREEN RIVER
NR DANIEL, AT WARREN BRIDGE APR-JUL 235 89
PINE CREEK
ABV FREMONT LAKE APR-JUL 97 93
NEW FORK RIVER
NR BIG PINEY APR-JUL 360 91
GREEN RIVER
FONTENELLE RESERVOIR, NR FONTENELLE APR-JUL 800 93
BIG SANDY RIVER
NR FARSON APR-JUL 62 107
GREEN RIVER
NR GREEN RIVER APR-JUL 830 95
HAMS FORK RIVER
BLO POLE CREEK, NR FRONTIER APR-JUL 62 95
VIVA NAUGHTON RESERVOIR APR-JUL 81 91
SMITHS FORK RIVER
NR BORDER APR-JUL 95 92
YELLOWSTONE RIVER
YELOWSTONE LAKE OUTLET APR-SEP 550 68
WIND RIVER
BOYSEN RESERVOIR INFLOW APR-SEP 760 94
BIG HORN RIVER
NR KANE APR-SEP 920 83
GREYBULL RIVER
NR MEETEETSE APR-SEP 102 51
SHELL CREEK
NR SHELL APR-SEP 69 96
SHOSHONE RIVER
BUFFALO BILL RESERVOIR INFLOW APR-SEP 510 63
CLEAR CREEK
NR BUFFALO APR-SEP 38 97
NORTH FORK POWDER RIVER
NR HAZELTON APR-SEP 9.4 90
SWEETWATER RIVER
NR ALCOVA APR-JUL 96 130
APR-SEP 103 129
SNAKE RIVER
JACKSON LAKE INFLOW APR-SEP 600 66
APR-JUL 540 66
GREYS RIVER
ABV PALISADES RESERVOIR, NR ALPINE APR-SEP 240 61
SALT RIVER
NR ETNA APR-JUL 210 61
ABBREVIATIONS USED:
ABV = ABOVE
BLO = BELOW
NR = NEAR
***ASSUMPTIONS***
--THESE FORECAST VOLUMES REFLECT NATURAL FLOW. ACTUAL OBSERVED FLOW
WILL LIKELY BE AFFECTED BY UPSTREAM WATER MANAGEMENT.
--ALL AVERAGES ARE FOR THE PERIOD 1971 THROUGH 2000.
--THIS OUTLOOK IS BASED ON RECENT OBSERVATIONS OF SNOWPACK AND
ASSUMES NORMAL PRECIPITATION FOR THE REMAINDER OF THE SNOW SEASON. IF
THE ACTUAL OBSERVED PRECIPITATION DEVIATES FROM THE NORMAL...THEN THE
ACTUAL OBSERVED RUNOFF WILL LIKELY BE DIFFERENT THAN THE FORECASTS IN
THIS OUTLOOK.
FORECAST CONDITITIONS...
FLOOD...RUNOFF FROM SPRING SNOWMELT IS FORECAST TO CAUSE MINOR
OR NO FLOOD RELATED PROBLEMS THROUGHOUT THE AREA.
IN THE TABLE BELOW, THE 90 THROUGH 10 PERCENT COLUMNS INDICATE THE
CHANCE THE RIVER COULD RISE ABOVE THE LISTED STAGE LEVELS. EXAMPLE:
THE WIND RIVER NEAR DUBOIS (7NW) HAS A FLOOD STAGE OF 5.0 FEET.
DURING THE VALID PERIOD THERE IS A ONLY A 50 PERCENT CHANCE THE
RIVER WILL RISE TO NEAR 4.1 FEET.
CHANCE OF EXCEEDING STAGES IN FEET AT SPECIFIC LOCATIONS
VALID 2/22/2005 - 5/17/2005
FS
LOCATION (FT) 90% 80% 70% 60% 50% 40% 30% 20% 10%
-------- ---- --- --- --- --- --- --- --- --- ---
SALT R
NEAR ETNA 6.0 3.1 3.2 3.4 3.5 3.6 3.7 3.8 4.0 4.1
VALID 2/28/2005 - 9/30/2005
FS
LOCATION (FT) 90% 80% 70% 60% 50% 40% 30% 20% 10%
-------- ---- --- --- --- --- --- --- --- --- ---
WIND R
DUBOIS WY 7NW 5.0 3.9 3.9 4.0 4.0 4.1 4.1 4.3 4.4 4.6
WIND R ABV RED CR
DUBOIS WY 12SE 5.6 5.6 5.8 5.9 6.0 6.1 6.4 6.7 7.1 7.4
***ASSUMPTIONS***
--THE NUMBERS CONTAINED IN THIS LONG-RANG PROBABILISTIC OUTLOOK
REPRESENT NATURAL FLOWS. THAT IS...FLOWS UNAFFECTED BY MAN-MADE
STRUCTURES IN THE BASINS SUCH AS DIVERSION DAMS AND RESERVOIRS.
--THIS OUTLOOK CONTAINS NUMBERS THAT ARE CALCULATED USING MULTIPLE
SCENARIOS FROM 18 OR MORE YEARS OF CLIMATOLOGICAL DATA. THESE NUMBERS
ALSO TAKE INTO ACCOUNT CURRENT CONDITIONS OF THE RIVER...SNOW
COVER...AND SOIL MOISTURE...AS WELL AS 30 TO 90 DAY LONG-RANGE
OUTLOOKS OF TEMPERATURE AND PRECIPITATION.
BY PROVIDING THE COMPLETE RANGE OF PROBABILISTIC NUMBERS...THE LEVEL
OF RISK ASSOCIATED WITH LONG-RANGE PLANNING DECISIONS CAN BE
DETERMINED. THESE PROBABILISTIC NUMBERS ARE PART OF THE NATIONAL
WEATHER SERVICE'S ADVANCED HYDROLOGIC PREDICTION SERVICES (AHPS).
VISIT OUR WEB SITE: http://www.crh.noaa.gov/riw/ahsp FOR MORE WEATHER
AND RIVER INFORMATION INCLUDING REAL TIME GRAPHS OF RIVER FLOW/STAGE AS
WELL AS PROBABILISTIC OUTLOOKS.
RIW/JTFAHEY