Spring in the Sierra can mean warm sunny days one week and stormy weather the next. The whiplash can be painful.
After a period of above average temperatures and the melt-freeze cycle dominating our backcountry pursuits, a series of fast moving storms are beginning to affect the region once again. The last time we experienced any notable precipitation was March 5th when we received around 7” of cold winter snow and a typically strong southwest flow.
Since then, temperatures have climbed to the 50’s near 10,000’ and even into the 60’s below about 9,000’. Coupled with good re-freezing on most nights at most locations, the snow pack has gained strength and settled (and melted too). During the warm-up, solar aspects saw a significant loss of snow cover with some slopes becoming completely bare below ~8000’. Loose Wet avalanches were observed in the Low to Mid elevations, slowly creeping into the upper elevations as temperatures continued to rise into unseasonably warm territory this last week.
The bond between the melt-freeze crust from last week’s high pressure and the moist new snow varies by aspect and elevation. At lower and middle elevations, the wet storm snow seems to have bonded relatively well to the wet surface underneath. At higher elevations where the snow surface never quite warmed through, and where winds have been depositing heavy, moist slabs since Tuesday morning, we can expect this bond to be more tenuous. On leeward slopes of about 35 degrees or steeper, and around features that promote drifting and loading, watch for round, pillow shaped wind drifts, cornice formation, and blowing snow. Use these clues to guide your terrain choices. Be cautious and make your decisions conservatively. Drum-like, hollow sounding snow indicates that you’re already standing on a wind loaded slope. Cracks shooting out from your feet should set off alarm bells in your head.