Turnagain Pass Avalanche Forecast

Yesterday there was evidence of the winds moving Monday’s snow around across the region. Scouring, anti-tracks and drifting were observed, especially along upper elevation ridges. A few small natural winds slabs from right after the storm were observed with the crowns mostly filled in.  There were no reports of human triggered winds slab avalanches in the advisory area but there was wind slab triggered in Summit Lake by a party skinning on the Tenderfoot ridge and a snowmachine triggered wind slab in Lost Lake. Northwest winds picked up in the evening and are forecast to remain strong throughout the day today. There is still some snow available for transport. Expect loading and slabs along ridgelines and look for pillowed or drifted snow. Northerly winds can funnel though Turnagain Pass from the South (especially at lower elevations) and there maybe loading on multiple aspects. Watch for shooting cracks and areas with stiffer snow. Steep, unsupported slopes that are loaded will be the most suspect. Slabs may be stiffer and harder to trigger today. They may be initially supportable and then fail above once out onto the slab. Look for blowing snow and pay attention to changing conditions.

Loose snow avalanches (sluffs): On steep slopes protected from the wind expect the new snow to sluff easily. These loose snow avalanches may be fast running and entrain snow quickly. 

Sunshine:  Remember that it is that time of year when we need to pay attention to the sun.  The sun can heat up Southerly aspects, and melt surface snow and cause small point releases in the loose new snow. This will be more of a concern if winds become calm this afternoon. This heating can also cause a slab sitting on a weak layer to become more reactive. Avoid steep solar aspect if you notice the surface snow becoming moist or you see roller balls or point releases under rocks. 

Wind effect on Eddies

Skier triggered sluff on Seattle Ridge

 Snowmachine triggered wInd slab Lost Lake. 

The overall snowpack structure across the advisory area is poor and it is important to keep in mind that larger slides breaking in persistent weak layers could still occur.  The new snow load Monday, combined with the winds over the past two days, has added to the overall weight/stress from the small storms last week. This incremental loading can slowly overload weak layers making them more prone to triggering. Furthermore, avalanches triggered in the upper layers of the snowpack, like a fresh wind slab, have the potential to step down to the buried weak layers. In the upper elevations a layer of buried surface hoar from Jan. 21st continues to show signs of reactivity and in the mid-elevations a layer of facets over a melt-freeze crust is suspect. Observers on Tincan noted finding both layers Monday in their snowpits. 

Deep Persistent Slabs:  At the high elevations above 3,000′, deeper persistent layers could ‘wake up’ if the wrong spot is found. Old weak layers of facets and buried surface hoar sit in the bottom half of the snowpack. This structure is most pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass, the Summit Lake area and Crow Pass.