Thursday, April 4, 2013

April 1st Salmon Snow & Streamflow Report

The monthly US NRCS "Basin Outlook Report" (BOR) was released late Thursday afternoon (April 4th).  Snow conditions and streamflow forecasts vary widely across the state.  Here's the meat of the BOR as it relates to The Salmon River:

Dryness since January is starting to outweigh the wet start to the water year from October through December. October, November and December started off the water year with abundant moisture, by New Years the Salmon basin water year to date precipitation was 128% of average. Now after three months of below normal precipitation water year precipitation is less than normal at 94% of average. Basin wide March precipitation was 58% of average.

This year’s January–March period ranks as second driest at Deadwood Summit and Banner Summit and third driest at Vienna Mine, Mill Creek and Morgan Creek sites since SNOTEL records begin in the early 1980s. It’s a wonder that snowpack percentages are still 84% of median as of April 1, but keep in mind the shift to the 1981-2010 medians is inflating the percentage. This year’s snow would be 73% of average based on the 1971-2000 averages. To help put this year’s snow in perspective with recent history a snow index is very useful. A snow index sums the snow water inches at a group of stations to compare years. The snow index for the Middle Fork Salmon, which combines snow water at Banner Summit, Deadwood and Morgan Creek SNOTELs indicates that this April’s snowpack is less than last year, but better than other recent low years like 2010, 2007, 2005 and 2004. Years with slightly better snow were 2009 and 2002. Since snowpack correlates with streamflow this is a good way to judge runoff. Streamflow forecasts range from
77% of average for the Salmon at White Bird to 83% of average for the MF Salmon. Remember you can expect the MF Salmon River’s snowmelt peak to occur when Banner Summit is half melted. Banner Summit only has 20 inches of snow water and could still accumulate a little more snow. Keep watching this site’s snow water to determine this year’s half-melt value. It will provide a clue as to when the snowmelt driven peak flow is past.

The Statewide Recreational Forecast is below the graphic.  The complete report is embedded at the end of this article.

With the onset of warm temperatures in early April, the rivers are now rising across the state. Winter’s
colder than normal temperatures kept the meager mid-elevation snowpack in place but it is now
melting to produce the early April flow increase. The Owyhee River had its snowmelt peak flow of
3,000 cfs for several days last month. It will rise again, but only with additional rains. The Bruneau
basin has a little more snow than last year, but don’t expect a much longer season unless it rains. Last
year the Bruneau River near Hot Springs was only above 800 cfs a handful of days. The MF Salmon
River is already at 3 feet, 2,100 cfs and will have a moderate season with moderate peaks, provided it
doesn’t rain. With the Salmon River at White Bird forecast at 77% of average, the main Salmon will still
have a good season without the potential for extended high flows. With the snow at 90% of median in
the Locsha and Selway basins, expect ideal river running opportunities as the streams are also
predicted at near average. The Payette snowpack and reservoirs will provide ideal flow levels through
the summer on the Payette. Additional snowmelt-streamflow relationship information is available on
the Idaho Peak Streamflow Resources internet page. Know your boating skill limits, and be sure to
watch the changing spring weather for more climatic variability extremes that may affect the melt
rates during the snowmelt season and produce sudden increases in flows.

Click here to download the document:

Many Thanks to the US NRCS, the Idaho Snow Survey Staff and especially Ron Abramovich, Water Supply Specialist, for providing our readers with this information on such a timely basis!

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