...WATER SUPPLY AND SPRING FLOOD POTENTIAL OUTLOOK FOR NEVADA AND--
EASTERN CALIFORNIA AS OF MAY 6 2011...
ISSUED JOINTLY BY THE NATIONAL WEATHER SERVICE AND NATURAL RESOURCES
CONSERVATION SERVICE...
1/WATER SUPPLY OUTLOOK...SUMMARY...
APRIL WAS COOL AND WET THROUGHOUT MUCH OF NEVADA AND EASTERN
CALIFORNIA. THE CENTRAL SIERRA NEVADA RECEIVED NEAR AVERAGE AMOUNTS
OF PRECIPITATION. HOWEVER...AS THE STORMS SWEPT ACROSS
NEVADA...PRECIPITATION INCREASED SUBSTANTIALLY...LEAVING MANY BASINS
FURTHER EAST WITH DOUBLE AVERAGE MONTHLY TOTALS. THE NOTABLE
EXCEPTION WAS SOUTHERN NEVADA...WHICH AGAIN FAILED TO ADD TO WHAT
WAS A PROMISING START TO THE WATER YEAR.
THE RELATIVELY COOL APRIL WEATHER SUBDUED SNOWMELT. STREAMFLOW
INCREASED SOMEWHAT...BUT HIGH ELEVATION SNOWPACK WAS PRETTY MUCH
UNTOUCHED DURING THE MONTH. THIS BEGAN TO CHANGE THE FIRST WEEK OF
MAY...WITH OVERNIGHT TEMPERATURES ABOVE FREEZING IN THE MOUNTAINS
AND SNOWPACKS BECOMING RIPE AND READY TO MELT ABOVE THE 7500 FOOT
ELEVATION IN THE CENTRAL SIERRA. STREAMFLOW HAS STARTED TO
INCREASE...RAISING CONCERNS FOR HIGH RUNOFF BETWEEN NOW AND LATE
JUNE THROUGHOUT THE REGION.
THE LARGE SNOWPACK IN THE SIERRA AND NORTHERN NEVADA...COMBINED WITH
A VERY WET WATER YEAR OVERALL HAVE KEPT STREAMFLOW FORECASTS HIGH.
COUPLE THIS WITH GOOD RESERVOIR STORAGE VOLUMES AND MEETING THE
REGIONAL WATER SUPPLY NEEDS FOR THIS SUMMER SHOULD BE EASY.
2/SPRING FLOOD POTENTIAL OUTLOOK...
SPRING FLOOD POTENTIAL IN NEVADA AND EASTERN CALIFORNIA DEPENDS ON
SEVERAL FACTORS...INCLUDING SNOWPACK...SOIL MOISTURE...RESERVOIR
STORAGE...AIR TEMPERATURES AND HOW MUCH RAIN THERE IS DURING THE
MELT PERIOD.
SPRING SNOWMELT FLOOD POTENTIAL IS ABOVE AVERAGE IN THE FOLLOWING
AREAS...
LAKE TAHOE TRIBUTARIES...
UNCONTROLLED TRIBUTARIES OF THE TRUCKEE RIVER ABOVE RENO...
EAST FORK...WEST FORK AND MAINSTEM CARSON RIVERS AND TRIBUTARIES
ABOVE LAHONTAN RESERVOIR...
WEST WALKER...EAST WALKER AND MAINSTEM WALKER RIVER AND TRIBUTARIES
ABOVE WEBER DAM...
MONO LAKE TRIBUTARIES...
UPPER OWENS RIVER TRIBUTARIES IN MONO AND NORTHERN INYO COUNTIES...
SNAKE RIVER BASIN IN NEVADA...
OWYHEE RIVER BASIN IN NEVADA...
EAST CENTRAL NEVADA...
HUMBOLDT RIVER AND TRIBUTARIES.
SPRING FLOOD POTENTIAL IS AVERAGE ON OTHER BASINS IN NEVADA AND
EASTERN CALIFORNIA.
THE ABOVE DESIGNATIONS ARE BASED ON MINIMAL PRECIPITATION DURING
SNOWMELT. HEAVY RAIN ANYTIME BETWEEN NOW AND THE PEAK SNOWMELT
PERIOD ANYWHERE IN NEVADA OR EASTERN CALIFORNIA COULD CAUSE SOME
DEGREE OF FLOODING.
FOLLOWING ARE THE REASONS FOR THE ABOVE AVERAGE CLASSIFICATION OF
SPRING SNOWMELT FLOOD POTENTIAL ON THE BASINS MENTIONED ABOVE...
ABOVE AVERAGE SPRING STREAMFLOW FORECASTS...
ABOVE AVERAGE SNOWPACK...
ABOVE AVERAGE SOIL MOISTURE...
ABOVE AVERAGE RESERVOIR STORAGE ON THE WALKER...OWYHEE AND TRUCKEE
BASINS. /NO FLOODING IS EXPECTED ON THE TRUCKEE RIVER DUE TO
AVAILABLE FLOOD CONTROL STORAGE./
AIR TEMPERATURE DURING MELT...UNKNOWN AT THIS TIME. HOWEVER...IF
TEMPERATURES REMAIN COOLER THAN NORMAL DURING THE MELT PERIOD...MELT
WILL BE SLOW AND OCCUR OVER A LONG PERIOD. THIS WOULD DECREASE
FLOOD POTENTIAL. IF MELT OCCURS VERY QUICKLY DUE TO A SUDDEN
WARMUP...THIS WOULD INCREASE FLOOD POTENTIAL.
RAINFALL DURING MELT...ALSO UNKNOWN AT THIS TIME. RAINFALL THIS TIME
OF YEAR IS MORE LIKELY IN NORTHEAST AND EASTERN NEVADA THAN EASTERN
CALIFORNIA AND WESTERN NEVADA. HEAVY RAIN COULD RESULT IN SOME
DEGREE OF FLOODING ANYTIME FROM NOW THROUGH LATE SPRING ANYWHERE IN
NEVADA OR EASTERN CALIFORNIA. HOWEVER...LITTLE OR NO RAIN DURING
THE MELT PERIOD TYPICALLY RESULTS IN ONLY MINOR TO POSSIBLY MODERATE
FLOODING...DEPENDING ON THE AMOUNT OF SNOWPACK.
3/APRIL 1 SNOWPACK...
EARLY MAY SNOWPACK CONDITIONS FOR NEVADA AND EASTERN CALIFORNIA ARE
PHENOMENAL. ALL AREAS IN THE REGION ARE WELL ABOVE AVERAGE WITH
MANY BASINS HAVING DOUBLE THE AMOUNT OF SNOW FOR THIS TIME OF THE
YEAR. THE UPPER HUMBOLDT RIVER BASIN HAS THE HIGHEST VALUE AT 224
PERCENT OF AVERAGE...WHILE THE WALKER RIVER BASIN HAS THE LOWEST
VALUE AT 153 PERCENT OF AVERAGE.
LAST YEAR THIS YEAR
BASIN PERCENT OF AVERAGE PERCENT OF AVERAGE
LAKE TAHOE ....................... 125 ................ 208
TRUCKEE RIVER .................... 120 ................ 188
CARSON RIVER ..................... 125 ................ 174
WALKER RIVER ..................... 113 ................ 153
NORTHERN GREAT ................... 92 ................ 184
UPPER HUMBOLDT RIVER ............. 107 ................ 224
LOWER HUMBOLDT RIVER ............. 69 ................ 178
CLOVER VALLEY & FRANKLIN RIVER ... 67 ................ 186
SNAKE RIVER ...................... 82 ................ 168
OWYHEE RIVER ..................... 82 ................ 197
EASTERN NEVADA ................... 147 ................ 208
4/PRECIPITATION...
APRIL WAS FAIRLY COOL AND WET IN MOST OF NEVADA AND EASTERN
CALIFORNIA. SEVERAL STORMS ADDED PRECIPITATION TO THE AREA. APRIL
PRECIPITATION WAS HIGHEST IN THE CLOVER VALLEY AND FRANKLIN RIVER
BASIN AT 245 PERCENT OF AVERAGE AND LOWEST IN THE LOWER COLORADO
RIVER BASIN AT 39 PERCENT OF AVERAGE. WATER YEAR PRECIPITATION IS
HIGHEST IN THE CLOVER VALLEY AND FRANKLIN RIVER BASIN AND EASTERN
NEVADA AT 157 PERCENT OF AVERAGE AND LOWEST IN THE LOWER COLORADO
RIVER BASIN AT 93 PERCENT OF AVERAGE.
APRIL WATER YEAR
BASIN PERCENT OF AVERAGE PERCENT OF AVERAGE
LAKE TAHOE ......................... 107 ................ 156
TRUCKEE RIVER ...................... 122 ................ 150
CARSON RIVER ....................... 92 ................ 139
WALKER RIVER ....................... 107 ................ 156
NORTHERN GREAT ..................... 237 ................ 148
UPPER HUMBOLDT RIVER ............... 187 ................ 148
LOWER HUMBOLDT RIVER ............... 165 ................ 146
CLOVER VALLEY AND FRANKLIN RIVER ... 245 ................ 157
SNAKE RIVER ........................ 175 ................ 140
OWYHEE RIVER ....................... 209 ................ 140
EASTERN NEVADA ..................... 131 ................ 157
LOWER COLORADO RIVER ............... 39 ................ 93
5/RESERVOIRS...
EARLY MAY RESERVOIR STORAGE IN NEVADA AND EASTERN CALIFORNIA WAS
IN GOOD SHAPE...WITH SOME RESERVOIRS MAKING RELEASES TO MAKE ROOM
FOR ANTICIPATED RUNOFF. RESERVOIR STORAGE WAS HIGHEST IN THE
TRUCKEE RIVER BASIN AT 126 PERCENT OF AVERAGE. THE LOWER COLORADO
RIVER BASIN WAS LOWEST AT 55 PERCENT OF AVERAGE.
BASIN PERCENT OF CAPACITY PERCENT OF AVERAGE
LAKE TAHOE ........................ 50 ................ 92
TRUCKEE RIVER ..................... 81 ................ 126
CARSON RIVER ...................... 63 ................ 83
WALKER RIVER ...................... 73 ................ 105
LOWER HUMBOLDT RIVER .............. 39 ................ 65
OWYHEE RIVER ...................... 97 ................ 125
LOWER COLORADO RIVER .............. 46 ................ 55
6/STREAMFLOW...
FORECASTS FOR NEVADA AND EASTERN CALIFORNIA STREAMFLOW ARE WELL
ABOVE AVERAGE. STREAMFLOW FORECASTS ARE HIGHEST FOR EASTERN NEVADA
AT 240 PERCENT OF AVERAGE. THE LOWEST EXPECTED FLOWS ARE IN THE
LOWER COLORADO RIVER BASIN AT 160 PERCENT OF AVERAGE.
PERCENT OF AVERAGE
BASIN 50 PERCENT CHANCE OF EXCEEDANCE
LAKE TAHOE ................................ 185
TRUCKEE RIVER ............................. 190
CARSON RIVER .............................. 200
WALKER RIVER .............................. 170
NORTHERN GREAT ............................ 175
UPPER HUMBOLDT RIVER ...................... 170
LOWER HUMBOLDT RIVER ...................... 168
CLOVER VALLEY AND FRANKLIN RIVER .......... 130
SNAKE RIVER ............................... 212
OWYHEE RIVER .............................. 160
EASTERN NEVADA ............................ 240
LOWER COLORADO RIVER ...................... 160
7/ APPROXIMATE DATES OF PEAK STREAMFLOW...
THE HIGHEST FLOWS OF THE MELT SEASON ARE EXPECTED AS FOLLOWS...
TAHOE BASIN...BETWEEN EARLY AND MID JUNE.
TRUCKEE BASIN...BY MID MAY.
CARSON BASIN...BETWEEN LATE MAY AND EARLY JUNE.
WALKER BASIN...BETWEEN EARLY AND MID JUNE.
MARYS RIVER...BETWEEN MID AND LATE MAY.
UPPER HUMBOLDT BASIN...BETWEEN LATE MAY AND MID JUNE.
LOWER HUMBOLDT BASIN...BETWEEN EARLY AND LATE JUNE.
8/ LONG RANGE WEATHER OUTLOOK FOR NEVADA AND EASTERN CALIFORNIA...
MAY PRECIPITATION IS EXPECTED TO BE BELOW NORMAL EAST OF A LINE FROM
ABOUT OWYHEE-MOUNTAIN CITY NV IN THE NORTH...TO DEATH VALLEY CA IN
THE SOUTH. IT IS EXPECTED TO BE NEAR NORMAL IN THE REST OF THE
REGION. MAY TEMPERATURES ARE EXPECTED TO BE ABOVE NORMAL SOUTH OF A
LINE FROM ABOUT BISHOP CA TO BAKER NV...AND NEAR NORMAL NORTH OF
THIS LINE.
THE LONG RANGE OUTLOOK FOR THE MONTHS OF JUNE THROUGH AUGUST IS FOR
NORMAL PRECIPITATION AND ABOVE NORMAL TEMPERATURES THROUGHOUT THE
REGION.
9/ FOR MORE DETAILED WATER SUPPLY AND STREAMFLOW FORECAST
INFORMATION FOR NEVADA AND EASTERN CALIFORNIA...PLEASE REFER TO THE
FOLLOWING WEB SITES /NOTE...ALL LETTERS IN WEB SITE ADDRESSES ARE
LOWER CASE/...
NWS CALIFORNIA NEVADA RIVER FORECAST CENTER...
HTTP://WWW.CNRFC.NOAA.GOV/
NATURAL RESOURCES CONSERVATION SERVICE...
HTTP://WWW.NV.NRCS.USDA.GOV/SNOW/INDEX.HTML
CALIFORNIA DEPT. OF WATER RESOURCES...
HTTP://CDEC.WATER.CA.GOV/
NWS CLIMATE PREDICTION CENTER LONG RANGE OUTLOOK MAPS...
HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/FORECASTS/
U.S. DROUGHT PORTAL...INCLUDING U.S. DROUGHT MONITOR...
HTTP://DROUGHT.GOV/
NNNN
Source: http://www.wrh.noaa.gov/total_forecast/getprod.php?wfo=rev&sid=REV&pil=ESF
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