Saturday, May 4, 2013

May 1 NRCS Basin Outlook Report

The May 1 status of The Salmon River watershed

As the winter finally morphs to spring, all eyes turn to watch and wonder about the snowpack.  How much snow did The Salmon River watershed actually receive?  What are the forecasts for runoff and stream flow?
Generally, the May 1st USDA NRCS Basin Outlook Report is the most anticipated and widely read of the monthly series from January to June.

Here is what the report says for The Salmon River:

"Four months and counting - that is how long it’s been since the Salmon basin had an above average amount of precipitation. Just to the north all SNOTELs in the Clearwater basin got more than their usual April precipitation, but the wet zone stopped just inside the Salmon basin. Only Mountain Meadows SNOTEL site, the Salmon basin’s most northern site, had above average precipitation for the month. Basin-wide precipitation was 75% of average in April, leaving water year to date precipitation at 91% of average. The Salmon basin snowpack peaked at about 80% of the 1981-2010 normal peak amount. Despite being less than normal this season’s snow remained near its peak amount from late March through late April thanks to melt during warm periods being balanced by additional accumulation during cool, stormy periods. Snowmelt in early April and again during the last week of the month produced two moderate streamflow peaks. There is still plenty of snow left to fuel another snow-melt driven peak. For the MF Salmon expect that peak to occur when the snow at Banner Summit SNOTEL is half melted, which this year will occur when 10 inches of snow water remains. 2007 had a similar snowpack and the MF Salmon had twin peaks in the 5500-6000 cfs range. If the weather stays warm this year’s snowmelt peak could occur by mid-May. Use the snow-stream graphs to track this year’s snowmelt and runoff: 

Depending on the weather, rain can always produce a later peak especially if it occurs before the snow is gone. Streamflow forecasts percentages decreased for the Lemhi from last month, but remained steady for most other points. The May-July streamflow forecasts range from 56% of average for the Lemhi to 80% for the SF Salmon. The MF Salmon is forecast for 80%, while the Salmon at Salmon’s forecast is 70%."

NRCS Water Supply Special Ron Abramovich described this winter's precipitation in a nutshell:

"Apparently, Mother Nature spent most of her snow budget during Christmas this year and forgot to save enough for the rest of winter. After a great start with abundant fall rains and snow, major storms avoided Idaho for the most part shortly after the winter solstice."

Abramovich went on to describe spring weather than would help augment water yield from the below-normal snowpack:

"What is certain and needed now to improve the runoff is rain. Cold and wet is better than just cold. Wet weather would reduce irrigation demand even more, allow farmers to utilize the spring precipitation to replace irrigation water and allow the water saved to be used later this summer when we know it will be dry. Another option to melt snow and increase efficiency or maximize the amount of water that reaches the reservoirs is to turn the heat up. This would increase snowmelt rates to 1-2 inches per day, exceeding maximum soil infiltration rates, allowing more water to reach the reservoirs. However, this option would not benefit natural streamflow water right holders as much, nor those with late summer river rafting trips."

As usual in each monthly Basin Outlook Report, Abramovich includes a Recreational forecast and perspectives:

"Snowmelt streamflow peaks have occurred in the Owyhee, Weiser, and Camas Creek near Fairfield along with other lower elevation watersheds. Cold temperatures and lack of rain near the end of April reduced snowmelt and kept streamflows at near record low levels in late April in the Payette, Boise, and Upper Snake. In contrast, streamflow levels in the Owyhee River and Camas Creek are approaching near record low because of the drought. On the positive side, snowmelt peak flows have not occurred yet on Salmon Falls Creek, Bruneau River and other higher elevation watersheds. Additional snowmelt streamflow relationship information is available on the Idaho NRCS Peak Streamflow Resources web page: This page includes streamflow recession graphs to view current trends, and a similar year that is based on the current snowpack, spring ENSO climatic conditions and analog years which are 2002, 1968 and 1963, or years with a similar flow pattern. Snow-streamflow comparison graphs are now automated and will be updated several times per week during the critical runoff season to provide guidance on snowmelt streamflow peaks."

Below is the complete May Basin Outlook Report in embedded format so that you can read it online without downloading it.  The NRCS link to the document is below the embedded version.

Here is the link to the full report:

No comments: