Northern San Juan

Snowpack

Markus Beck · Jan 16, 2013 · Northern San Juan

Weather

Downright balmy after the freezer of the past few days! Overnight lows, despite a clear night, weren't that cold and day temps reached low-mid 20s; on S'erly slopes it was really comfy even without wearing the extra downie! Calm winds dominated below treeline, though moderate NW'ly winds at higher elevations produced minor wind loading.

Snowpack

Variable & Complex! Unusual weather is creating unusual snowpack and avalanche conditions. Recent winds transported the storm snow all over the mountain sides. The only pattern is that there is no pattern: wind loaded areas are spread around the entire compass around and above treeline. Generally, on S'ly slopes, the spx is thin (though it may look deeper from a distance due to the recent storm and wind deposited snow masking the thin spots). The deepest Hs is found around the top of RMP, the S side still a bit more than the N side. The recent strong winds have scraped bare of snow many slopes in the alpine and formed hard slabs in others. Soft snow can be found in wind sheltered and leeward areas, even above treeline to some extent in isolated areas. Below treeline, the entire spx consists of large facets. Around treeline wind and sun have affected the spx and a slab of varying hardness and thickness atop a faceted base is common. A snowpit on a small wind loaded slope (discernible on topo map: bump at 12,000ft, 24dgr, Hs 48-63cm, S aspect, directly below and W of Ohio Pk) showed: large dh, P faceted crust 1cm thick, 1F-F wind slabs ~30-50cm thick / CTsc on dh upon isolation (3), ECT-P7s(1). Approaching this slope, I caused 2 collapses that propagated est 50ft. Leaving this slope, I remote triggered from 20ft away an R4D1 on 24-30dgr adjacent slope (see pics). This spx structure - wind slab on top of dh - is widespread on all aspects around and above treeline though most pronounced around treeline. Slopes with this structure are very sensitive to human triggering and will propagate readily across full dimension. Slopes with this spx structure at 30+dgr should be avoided- even small pockets running into concave terrain features will be trouble! Below treeline especially on shaded slopes W-N-E, the spx consists of 3-5ft of fully faceted large dh. There, on very steep slopes, we created loose dry avalanches that packed a surprisingly good punch (enough to push a skier off his/her feet as experienced when we "surfed" such slopes up to 48dgr).