Thursday, April 20, 2017

Spring Snowmelt Flood Potential Moderate to High Star Valley Region

Quick Synopsis:

Mountain snowpack and associated snow water equivalents (SWEs) across central 
through western Wyoming continued to be much above average by the middle of April; 
while SWEs across basins in southeastern Wyoming were generally below average. 
  SWEs at the peak snowmelt runoff elevations (8,500’ – 10.000’) continue to be the 
highest across the Wind and the Upper Green Basins at 170 to 190 percent of median. 
 The Laramie, Upper North Platte, and Little Snake Drainages had SWEs at near
 75 to 90 percent of median at the peak snowmelt runoff elevations.
This outlook is based on various diverse hydrological factors such as:  snow water
 equivalents (SWEs) in the mountain snowpack, basin morphology (i.e. how basins 
respond to snowmelt runoff),  antecedent soil moisture, amount of forest canopy
 damage, recent burn scars, low elevation snow depths, and likely temperature and 
precipitation trends during late spring/early summer.


High potential for flooding associated with snowmelt is expected over several
 basins across the Little and Big Wind Watersheds…       
High potential for flooding associated with snowmelt is expected over several
 basins of the Upper Green Basin…
Moderate to High potential for snowmelt flooding is expected over headwater 
basins of the Snake River Drainage (to include the Salt River Drainage)
Moderate to High potential for flooding due to snowmelt is expected over
 portions of the North and South Forks of the Shoshone River Basin…
Moderate to High potential for snowmelt flooding is predicted over portions 
of the of the Sweetwater River Watershed…
Moderate potential for flooding associated with snowmelt is also expected 
across the upper to middle portions the of the Little and Big Wind Watersheds, 
the middle to upper portions of the Upper Green Drainage, the lower and/or
 upper potions of the North/South Forks of the Shoshone Basin, the upper 
and lower sections of the Upper Bear Watershed, and several basins across
 the Snake River Watershed.
…All other headwater basins (Upper North Platte, Laramie, Little Snake, Powder, 
and Tongue Basins) across Wyoming can expect a generally Low potential for
 flooding due to springtime snowmelt...
This will be the LAST outlook for the 2017 season

Following are several SNOTEL graphs as of April 20 
comparing normal vs current levels of snow water 
content and total precipitation since Oct, 1 2016. 

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