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Valid until Monday 25 February, 2013.
Confidence: Fair. Uncertainty about precipitation amounts and wind strength.
Past Weather: The Island Alps saw between about 20 and 70cm of new snow since Wednesday with most of this coming in the storm that started early Friday with the greatest amounts on the west coast of the island. Winds were mostly moderate with perhaps some guests to strong in the alpine from the south east to south west. Freezing levels spiked to near tree line on the west and east island on Thursday but remained lower on the north island.
Main Concerns: (Avalanche problems)
Storm Slab - Storm slab from significant snow fall exists on all aspects and at all elevations. This slab can be triggered by humans on Saturday and will fail naturally on Sunday. Storm slabs could produce avalanches from small to at least large enough to bury, injure or kill a person.
Wind Slab - Significant quantities of snow (indeed near biblical on the west coast) combined with strong winds have created widespread wind slab on west through north to east aspects at tree line and in the alpine. These slabs can be triggered by humans on Saturday and will fail naturally on Sunday. Avalanches could be very large.
Persistent Slab - A weak layer of snow exists below our previous storm snow which fell early this week. This layer delivered easy test results on Friday. The layer exists at all elevations and on all aspects and could be easily triggered by humans on Saturday and may fail naturally on Sunday. Avalanches would likely be small below tree line but could be large to very large at tree line and above.
Overnight Friday to Saturday - 5 to 25cm snow left in the system. Winds moderate gusting to strong and mostly from the south west. Freezing level as low as 400m overnight rising to 800m Saturday.
Sunday - a significant system bringing 10 to 40cm of snow. Winds variable and up to strong likely focused on the south east in most areas. Freezing level likely 1000m or below in most areas.
Monday - At most a trace of precipitation. Winds moderate west to north west. Freezing level 800-900m.
Very limited observations due to low visibility. A natural avalanche cycle may have occurred in the alpine on Friday or may occur Friday night/Saturday.
20 to 70cm of storm snow overlies 15-30cm of previous storm snow from earlier this week. The previous storm snow sits on a crust of variable thickness. This interface produced easy, planar results in tests at Mount Cain on Friday afternoon including a Rutsch Block 2 result. Storm snow has been and will continue to be moved by moderate to strong winds at tree line and in the alpine forming wide spread wind slab on east through north to west aspects. Below the above mentioned weaknesses the island snowpack is generally well settled and strong.
Stay out of avalanche terrain this week end. Stick to low angled and/or well forested slopes.
Prepared by: Jan Neuspiel and The Cain Crew.
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