Observation: Public
Observation Details
Name:
Enji CooperObservation Date:
March 1, 2023Submitted:
March 1, 2023Zone or Region:
East CentralActivity:
XC Skiing/SnowshoeingLocation:
Tumwater Mountain (North and South)Triggered Avalanches
Did you trigger any avalanches?
YesWas it intentional?
NoAvalanche Type:
Soft SlabSize:
Size 1: Relatively harmless to peopleElevation:
3.75k’ and upAspect:
NComments:
Most of the soft slabs of note broke on the north side of Tumwater Mt (north peak). The characteristics appeared like surface layer wind slabs. I did a snowshoe cut and observed a dispersed resistant planar break (hand shear tests throughout the day confirmed this). The slab didn’t seem like it was strong enough yet to be of serious concern, but there was potentially enough to trigger a small D2 avalanche. It does however present a potential smaller “model” of wind distribution/strength in the area.Observed Avalanches
Did you observe any avalanches?
YesAvalanche Type:
Dry Loose (Sluff)Size:
Size 1: Relatively harmless to peopleElevation:
ATLAspect:
NComments:
Triggered D1 sluffing on descent. The issue wasn’t exclusively on northern aspects, but was influenced by solar input and where the wind transport had collected.Signs of Unstable Snow
Did you see shooting cracks?
Yes, IsolatedDid you experience collapsing or whumpfing?
NoObservations
Temp at arrival at 9:30 was 19 degrees; temp at departure at 6 was 38 degrees. Skies were mostly clear in morning, becoming broken/overcast as the day progressed.
Snow well below treeline and 3k’ was pencil hard at least. Crampons would have helped in this area. Snow above 3k’ and below treeline was small amounts of storm snow over at least pencil hard crust. Snow on sun exposed aspects (SE, etc) NTL/ATL was storm snow which was poorly bonded to at least pencil hard crust. Was up to 6” deep. Snow in shaded areas resembled consolidating wet loose. The fresh storm snow hid terrain traps (boulders, logs), so travel was slow. Due to the poor bond between the new and old layers, I had to use a combination of my snowshoes (which have less aggressive crampons) and my steel crampons. I found large facets in areas after I broke the stout surface layer with my crampons.
Wind fetch became very apparent NTL/ATL along the ridge in leeward areas. My snowshoe penetration was up to 1.5’, but by and large it seemed closer to 6” on average. A large wind event was taking place on the ridge in the early afternoon and large amounts of wind transport were present. I felt like I got sandblasted a few times by strong gusts with wind transport. Wind transport was predominantly moving from west side of ridge to east side of ridge.
Wind was stronger than forecast this morning per NOAA. It was 10+ mph sustained and there were gusts over 25mph (please refer to weather station on north summit for accurate measurements). Wind chill felt like it was in high single digits or low teens at its strongest.
Small surface and near surface facets were present and very visible in the morning. I didn’t see any surface hoar with my naked eye, but I wasn’t looking very closely.
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