This document discusses the lack of snowpack and below average precipitation in the western US, particularly Idaho and Montana, during the 2014-2015 winter season. It provides photos and data showing much of the precipitation fell as rain rather than snow. This has led to drought conditions with the 4th lowest snowpack levels on April 1st since 1961 and irrigation shortages projected. More precipitation is needed, particularly snowfall, to improve water supply conditions.

1. Photo taken by Ray Gadd March 11, 2015 looking
east and south over Big Wood River valley
illustrating lack of snow on south facing slopes.
Photo by Ray Gadd
Ron Abramovich
Water Supply Specialist
USDA NRCS Snow Survey
Boise, Idaho
• Pacific Northwest Snowpack & Water Supply Update
• Water Year to Date Precipitating vs. Snow Water Equivalent
• Impacts of Rain vs. Snow to Produce Adequate Irrigation Supplies

2. Photo by Ray Gadd
Photo taken by Ray Gadd March 11, 2015 looking east over Ketchum in Big
Wood River valley illustrating lack of snow on south facing slopes.
Lost-Wood Divide SNOTEL Site
Impacts on Ski Season
Ski Races
Skier Days
Passes Sold

7. Combined March
Temperature &
Below Normal
Precipitation
Deteriorated Idaho’s
Snowpack
7-10 F
16%

11. Apr 1 Snow 4th Lowest
Since 1961

12. Montana --- Mean temperature departure & precipitation falling normal Nov 1 – Mar 31:
Twelve Mile: 3.8F Beaver Creek: 5.1F
Normally 70% precip falls as snow Normally 97% precip falls as snow
2015 60% fell as snow 2015 92% fell as snow

13. Idaho --- Mean temperature departure & precipitation falling normal Nov 1 – Mar 31:
Graham Guard: 4.9 F Jackson Peak: 5.1 F
Normally 75% precip falls as snow Normally 92% precip falls as snow
2015 60% fell as snow 2015 84% fell as snow

14. Washington --- Mean temperature departure & precipitation falling normal Nov 1 – Mar 31:
Stampede Pass: 5.0 F Paradise: 5.3 F
Normally 80% precip falls as snow Normally 92% precip falls as snow
2015 34% fell as snow 2015 46% fell as snow

15. Amount of Precipitation (Rain) Needed
Depends on:
• Rain Intensity
• Snow on Ground or Not during the Event
• Spring Rains in Big Wood River Model
Central Idaho
– Need ~0.75” the 1st day to prime soils
– Need ~0.3” the 2nd day to produce runoff
• Snow Melt Rates – similar to daily rainfall
are key sustaining Spring Streamflow

16. • Key is Knowing Snow Line Elevation in your Basin –
make better use of MODIS snow cover area data
• Eastern Idaho: May 2010 ~1.5” in 24 hrs with snow on the valley floor produced
flood event
• TWICE in Payette Basin: Jan 1997 & May 2010: 3.0+” in 24 hrs is Key Indicator for
Brundage Resv SNOTEL nr McCall - led to major flooding when snow present

17. Climate Variability
Cuts from 2012 Idaho Water Supply Reports:
March 2012
Snowmelt started melting two weeks earlier than normal.
Warm storms produced record high March precipitation
records at 25 SNOTEL sites. Rain increased snowmelt at mid-
elevation stations across the state.
April 2012
Record April temperatures reached 90 F in valleys and 70 F in
the mountains… this heat wave was likely the hottest in April
since 1875.
Add 1-2 inches of rain on April 26 increased streams to
record high levels for this time of year.

18. 2012 Record starts 1911
2012

19. May
1
Jackson Peak SNOTEL Boise Basin 7070 feet
April 2013 Rain on Snow Event – snowmelt rates in Boise basin were at
record high levels for this time of year melting at an 1” per day in the large
snow covered areas up to ~8,500 feet.
For 5 days, April 21-26
- melt rate was 0.8 to 1.2”/day,
- normal melt rate is 0.3”/day
Apr
1

20. Looking into Salmon River Headwaters June 12, 2008
Better Use of MODIS Snow Covered Area
High elevation zone – produces late summer streamflows
Mid elevations – produces majority of annual streamflow
Lower elevations – populated valleys - often transient
snowpacks that are more influenced by rainfall

21. Oct 1, 2013 Event
3200 CFS from
3+ inches in 24 hrs
at Deadwood &
Banner SNOTEL sites
A non-event for total
water supply BUT helps
in other ways
Summer Rain Event

22. From Boise NWS: Southern Idaho August 5-6, 2014
24 Hour rainfall totals from 3 PM to 3 PM on

23. Wilson Creek SNOTEL
Magic Mountain
SNOTEL
Increased Soil Moisture to
Levels seen in Spring from
Snowmelt
• Winter Wheat planted in
some wettest levels ever.
• Spring 2015 – Spring Wheat
planted in very dry SM levels

24. 0
50
100
150
200
250
300
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
[mm]
Monthly Evapotranspiration at the Twin Falls Agriment Station
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010

26. 0
2,000
4,000
6,000
8,000
10,000
12,000
CFS
Adjusted Average Daily Flow at Snake River near Murphy
1981-2015
Minimum Streamflow at the Murphy Gaging Station
Unadjusted Average Daily Flow 2014
Minimum of Record (1981-2014)
10th Percentile (1981-2014)
30th Percentile (1981-2014)
Median (1981-2014)
3-day Average of the Adjusted Average Daily Flow (AADF)

27. Dry, Warm April has
produced Irrigation
Demand:
Over 300% of
Average

28. Southwest Owyhee
County 4/8/15

29. IDAHO SURFACE WATER SUPPLY INDEX (SWSI) April 1, 2015

32. April 2015 5 Exceedance Forecasts Volumes Compared to
Ag Threshold Shortages (KAF)

34. Estimated Surplus Threshold is 70 KAF

35. Boise R @ Glenwood flow > 6700 cfs
13 years since 1982
Flood stage is 7,000 cfs
Est Surplus
Threshold

36. Recreational
Users

37. 2011 had a 4 month
boating season on
the Owyhee with
flows over 1,000 CFS!

38. Similar Year
2014 & 1959
And pray for
more Snow &
Rain!
2014
1959

39. Rain is good but snow is
better.
Spring Precipitation can
make or break the
streamflow forecast
Questions/Comments