• Modeled Snowmelt contributed between 0-23% of the total basin input during the top-10 extreme storms

• Dependent on Basin area shape, Forest cover, and the timing of the storm’s rain-snow transition.

How Important is SnowDuring Rain-on-snow Floods

over the Western U.S. Mountains?

Nic Wayand, University of Washington

1-year in the life of snow in the rain-snow transition zone

Snoqualmie Pass, Central Washington Cascades, USA.

“Typical” Storm

SNOWFALL

RAINFALLRUNOFF

RUNOFF

No runoff production

Elevation Z1AREA contributing overland runoff to stream

Photo credit: Flickr.com User: Lucas – K Lu

Slide by Mark Raleigh

RUNOFF

Rain-on-Snow Event

SNOWFALL

RUNOFFRUNOFFRUNOFF

Elevation Z2

Rain-on-Snow event produces Larger AREA contributing overland runoff to stream

Warmer Storm(1 week later)

Elevation Z1

ΔZ RAINFALL

Photo credit: Flickr.com User: Lucas – K Lu

Slide by Mark Raleigh

Snowcover exposed to warm, windy weather

Snow Depth

Elev

ation

More Snow at Higher Elevations

Potential melt

Snow depth

Maximizing Snowmelt

More Energy for melt at Lower Elevations

Sweet Spot for Melting Snow

Warmer Temperatures

Melt Energy

Using a Simplified basin modelRain-snow elevation Basin Shape Basin Forest Cover

Area of Melting Snow

Low Rain-snow transition

High Rain-snow transition

Area of Melting Snow

Photo credit: Flickr.com User: Lucas – K LuTop: http://cascadeclimbers.com/ User: off_the_hook

Bottom: http://thesnowtroopers.com/ User: Sting

Uniform Area Basin

“Fat” Area Basin

Lots of Forest

Clearings

Elev

ation

Elev

ation

SnowfallRainfall

Snowfall

Rainfall

Snow

mel

t Inp

ut (%

)

San Joaquin

basin, CA

Snoqualmie

basin, WA

E. North Fork Feather

basin, CA

Less

sno

wm

elt

Mor

e sn

owm

elt

High school Outreach: Rain-on-Snow Lesson

Video snap shot goes here

Link to materialhttp://tinyurl.com/oqo8ml7

Outreach videohttp://youtu.be/CWeR7_yu6H8