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

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 SeasonSki RacesSkier DaysPasses Sold

Combined March Temperature & Below Normal Precipitation

Deteriorated Idaho’s Snowpack

7-10 F

16%

Apr 1 Snow 4th Lowest Since 1961

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

2015 60% fell as snow 2015 92% fell as snow

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

2015 60% fell as snow 2015 84% fell as snow

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

2015 34% fell as snow 2015 46% fell as snow

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

• 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

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.

2012 Record starts 1911

2012

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

Looking into Salmon River Headwaters June 12, 2008Better 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

Oct 1, 2013 Event 3200 CFS from 3+ inches in 24 hrsat Deadwood & Banner SNOTEL sites

A non-event for total water supply BUT helps

in other ways

Summer Rain Event

From Boise NWS: Southern Idaho August 5-6, 201424 Hour rainfall totals from 3 PM to 3 PM on

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

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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

[mm

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Monthly Evapotranspiration at the Twin Falls Agriment Station

1991

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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)

Dry, Warm April has

produced Irrigation

Demand:

Over 300% of

Average

Southwest Owyhee

County 4/8/15

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

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

Estimated Surplus Threshold is 70 KAF

Boise R @ Glenwood flow > 6700 cfs

13 years since 1982

Flood stage is 7,000 cfs

Est Surplus Threshold

Recreational Users

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

Similar Year 2014 & 1959

And pray for more Snow & Rain!

20141959

Rain is good but snow is better.

Spring Precipitation can make or break the

streamflow forecast

Questions/Comments