February 2011 Wyoming Spring Flood Potential Outlook---issued February 25, 2011

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

Current SWE trends vs Historic SWEs for selected basins:

Snake River Basin:

·        SWEs were 100 to 120 percent to normal in early February 

·        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.

Upper Green Basin:

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

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

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

Shoshone River Basin:

·        SWEs were 105 to 120 percent of normal in early February.

·        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.

Wind River Basin:

·        SWEs were 90 to 100 percent of normal in the southern Wind River Basin and 100 to 115 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 approaching record 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 inline 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.

Upper North Platte River Basin:

·        SWEs were 120 to 130 percent of normal in early February.

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

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

Laramie River Basin:

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

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

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

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 2010 Snowmelt Runoff Flood Potential Outlook graphic:



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