Details

• Date: 2013/12/29

• Observer: Spencer Logan
• Organization: Forecaster, CAIC

Location

• BC Zone: Front Range
• Area Description: Arapaho Lakes

Weather

• Ridgeline Wind Speed: 20-30 mph
• Ridgeline Wind Direction: W
• Wind Loading: Intense
• Temperature: 15 F
• Sky Cover: Scattered
• Depth of New Snow: 20 cm
• Depth of Total Snow: 120 cm

Snowpack

Snowpack Obsvervation Comments: NE-E-SE below treeline Average snowpack depth was 100 cm. In most places, upper portion of old snowpack was 4F and supportable. On very steep slopes, old snowpack was shallow and faceted, and full-depth loose avalanches were easy to trigger.

Snowpack Obsvervation Cracking: Shooting Collapsing: Rumbling Persistent Weak Layer: Yes Comments: NE-E-SE-E near treeline Intense wind loading near treeline. In the morning, slabs were 4F and 30 to 60 cm thick. Four hours later in the same location, slabs had stiffened to 1F without changing thickness. All wind slabs are sitting on low density storm snow. Wind slabs were very touchy, but would not avalanche very far on slopes less than 35 degrees. Below the storm snow, the old snowpack interface is either very slick, P to K-hard old wind slabs or a layer of near surface facets on top of 4F to 1F hard wind slabs. This could make for a very piece-meal, variable PWL once the storm snow settles. The old snowpack stratigraphy was basically one slab, ranging from 4F to K as above, and depth hoar. Typical of such a windy spot, snowpack depth and layer thickness varied considerably based on local wind patterns. HS ranged from 0 to 200 cm. Got some isolated, rumbling collapses in the depth hoar. Found one slope that collapsed naturally, but was not steep enough to avalanche. Followed cracks to the ground for over 100 meters, and it looked like they continued for another 100.

Avalanches

	Date	Location/Path	#	Elev	Asp	Type	Trig	SizeR	SizeD
	2013/12/29	East Portal	3	TL	E	SS	N	R1	D1.5
Date: 2013/12/29 Observer: Spencer Logan Organization: Forecaster, CAIC Area Description: Very steep slopes at the upper end of treeline elevation band Landmark: East Portal Average Slope Angle: 35 ° Sliding Surface: S - Within Storm Snow Weak Layer Grain Type: Precipitation Particles Average Crown: 30 cm Average Width: 10 m Maximum Width: 30 m Average Vertical: 100 ft Maximum Vertical: 200 ft Comments: these ran between 1100 and 1230
	2013/12/29  †	East Portal	1	>TL	SE	SS	N	R2	D2
Date: 2013/12/29 (Estimated) Observer: Spencer Logan Organization: Forecaster, CAIC Area Description: Arapaho Lakes, prominent path off SE ridge of Radiobeacon Landmark: East Portal Sliding Surface: I - New/Old Interface Average Crown: 30 cm Average Width: 150 m Average Vertical: 250 ft Comments: Dimensions estimated, crown drifted in