March 2011 Wyoming Spring Snowmelt Flood Potential Outlook--issued March 24, 2011

Snow water equivalents (SWEs) in early March coninued above average (around 120 percent of normal) across Wyoming’s headwater watersheds. 

Current SWE trends vs Historic SWEs & Peak Flow Probabilities for selected basins:

Snake River Basin:

        ·        SWEs were 100 to 110 percent to normal in early March      

        ·        Current SWE trends are above the 30-year normal--but well below the record 1996 and 1997 SWE years.

        ·        LOW to MODERATE potential for headwater spring snowmelt flooding.

      ·       Snake River near Jackson

          21 - 40% chance:  >15,000 cfs

 

          Flood flow =  20,000 to 22,000 cfs

Upper Green Basin:

          ·        SWEs were 100 to 110 percent of average in early March.

 

 

    ·        LOW TO MODERATE potential for headwater spring snowmelt flooding across much of the basin. 

    ·      Green River near LaBarge

             21 - 40% chance:  >10,000 cfs

             Flood Flow = 12,000 cfs

    Shoshone River Basin:

    ·        SWEs were 100 to 110 percent of normal in early March.

    ·        Current SWE trends are slightly above the 30-year normal--and are below the record SWE years of 1996 and 1997.  SWE trends are above SWEs that produced record runoff in 1981 and 1991.

    ·        MODERATE potential for headwater spring snowmelt flooding across most of the basin---except MODERATE to HIGH flood potential across extreme upper portions of the North Fork of the Shoshone River.

    ·       North Fork Shoshone River near Wapiti

    41 - 60% chance:  >8,000 cfs

    Flood Flow =  9,000 to 10,000 cfs 

    Wind River Basin:

    ·        SWEs in early March were 90 to 100 percent of normal in the southern Wind River Basin and 100 to 110 percent of normal across the northern Wind River Basin.

    ·        Current SWE trends are above the 30-yr normal in the northern portions of the basin with SWE trends are below SWE years of 1999 and 1986---but well below the all-time SWE year of 1997.  Across southern portions of the basin, SWE trends are well below the record SWE years of 1999 and 1986---but still in-line with SWE trends seen in 2010.

    ·        MODERATE potential for headwater spring snowmelt flooding across the northern Wind River Basin and LOW to MODERATE headwater spring snowmelt flooding across the southern Wind River Basin.

    ·        Wind River near Dubois

               41 - 60% chance:  >1,200 cfs

               Flood Flow =  1,400 - 1,500 cfs

    ·        Wind River near Crowheart

              41 - 60% chance:  >8,000 cfs

              Flood Flow =    9,000 - 9,500 cfs

    ·        Wind River at Riverton

              41 - 60% chance: >5,000 cfs

              Flood Flow =  5,000 - 5,500 cfs

    ·        Middle Fork Popo Agie River near Lander

              20 - 40% chance:  >2,000 cfs

              Flood Flow = 2,500 - 3,000 cfs

    ·        Little Popo Agie River near Lander/Hudson

    21 - 40% chance:  >1,000 cfs

             Flood Flow = 1,400 - 1,500 cfs

    Upper North Platte River Basin:

    ·        SWEs were 125 to 135 percent of normal in early March.

    ·        Current SWE trends are near the record SWE years of 1982, 1986 and 1997--and well above the SWE trends of 2009 and 2010.

    ·        HIGH potential for headwater spring snowmelt flooding across the Upper North Platte River Basin.

    ·        Encampment River near Encampment/Riverside

              >80% chance:   2,800 - 3,000 cfs

              Flood Flow =  2,800 - 3,000 cfs

    ·        North Platte River at Saratoga

             >80% chance:  10,500 - 11,000 cfs

             Flood Flow =  10,500 - 11,000 cfs

    ·        North Platte River at Fort Steele/near Sinclair

             >80% chance:  10,500 - 11,000 cfs

             Flood Flow:  10,500 - 11,000 cfs

    ·        Rock River near Arlington

             61 - 80% chance:  >2,000 cfs

             Flood Flow = 2,500 - 2,700 cfs

    Laramie River Basin:

    ·        SWEs were 120 to 135 percent of normal in early March.

    ·        Current SWE trends are near the record SWE years of 1984, 1986, and 1997--and above the SWE trends of 2009 and 2010.

    ·      HIGH potential for headwater spring snowmelt flooding across the Laramie River Basin.

    ·        Laramie River at Laramie

    >80% chance:  2,000 - 2,200 cfs

    Flood Flow = 2,000 - 2,200 cfs

    Big Horn River Basin:

    ·        SWEs were 110 to 120 percent of normal (western Big Horn Mountains) in early March.

    ·        Current SWE trends are above the 30-yr normal—but below nearing  the record SWE years of 1986,1997, and 1999. (western Big Horn Mountains). 

    ·      LOW to MODERATE potential for headwater spring snowmelt flooding across the eastern Big Horn River Basin.

    ·        Big Horn River near Basin

    41 - 60% chance:  >11,000 cfs

    Flood Flow = 11,000 - 12,000 cfs

     Powder River Basin:

    ·        SWEs were 105 to 115 percent of normal in early March.

    ·        Current SWE trends are above the 30-yr normal—but below nearing  the record SWE years of 1986,1997, and 1999.  

    ·      MODERATE potential for headwater spring snowmelt flooding across the basin.

    ·        Clear Creek at Buffalo

              41 - 60% chance:  >1,000 cfs

              Flood Flow =   1,400 - 1,500 cfs

    ·        Middle Fork Powder River near Kaycee

    41  - 60% chance:  >1,200 cfs

             Flood Flow = 1,500 - 1,600 cfs

    Tongue River Basin:

    ·        SWEs were 100 to 105 percent of normal in early March.

    ·        Current SWE trends are above the 30-yr normal—but nearing  the record SWE years of 1986,1997, and 1999.  

    ·      LOW TO MODERATE potential for headwater spring snowmelt flooding across the basin.

    ·        Big Goose Creek near Sheridan

             21 - 40% chance:  >1,000 cfs

             Flood Flow = 1,700 - 1,800 cfs

    ·        Little Goose Creek near Big Horn

             21 - 40% chance:  >800 cfs

             Flood Flow = 1,050 - 1,100 cfs 

    Little Snake River Basin:

    ·        SWEs were 110 to 120 percent of normal in early March.

    ·        Current SWE trends are above the 30-yr normal—but below record SWE years of 1996 and 1997.  

    ·      MODERATE TO HIGH potential for headwater spring snowmelt flooding across the Little Snake River Basin.

    ·        Little Snake River near Savery/Dixon/Baggs

              61 - 80% chance:  >6,000 cfs

              Flood Flow = 7,000 - 7,500 cfs 

    Upper Bear River Basin:

    ·        SWEs were 125 to 140 percent of normal in early March.

    ·        Current SWE trends are well above the 30-yr normal—and above   record SWE years of 1986 and 1995.  

    ·      HIGH potential for headwater spring snowmelt flooding across the Upper Bear River Basin.

    ·        Bear River near Stateline and Evanston

              >80% chance:  >3,000 cfs

               Flood Flow =  3,500 - 3,800 cfs

    Other factors that lead to this outlook include:  basin geometry/morphology, biological influences (i.e. beetle kill areas in southeast Wyoming), and advice from outside sources and experts.

    Snowmelt flood potential in Wyoming is greatly influenced by the amount of mountain snowpack.  The additional accumulation of snowpack during late April through early June is very crucial to the magnitude of runoff flooding that headwater basins across Wyoming will experience.  Bottom line is that a lot can happen between now and the onset of the annual spring runoff when it comes to the potential for flooding.

    The complete Wyoming Spring 2011 Snowmelt Runoff Flood Potential Outlook graphic:


            

 

  • Current SWE trends are above the 30-year normal--but are below 1986 and 1997 SWE years---which were well above average runoff years.


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