Winter is still hanging on in the alpine, with a fresh hit of snow arriving overnight. The new snow may be reactive in wind loaded features or where it sits over a crust. Check out our latest forecaster blog on managing these not-quite-yet-spring conditions.
Cornices become weak with daytime warming. Cornice falls are dangerous in their own right and they can also trigger slabs on slopes below. Their large mass can trigger deeper slabs on buried crusts in the upper snowpack that a single rider wouldn't trigger on their own.
New snow may be most reactive where it is wind affected or sits over a crust. In areas where the bulk of snow arrived overnight may see some wind effect most likely isolated to immediate lees of ridgecrests and roll-overs in wind exposed alpine terrain.
Light precipitation spreading north to south overnight Saturday into Sunday. Local enhancements of up to 20 cm may be found on southwest facing slopes along the western border of the region. Below the freezing level, precipitation will fall as light rain.
Saturday night: 5-10 cm in the north of the region. Moderate to strong southwest wind. Alpine temperatures around -3. Freezing level 2000 m.
Sunday: 5-10 cm in the south of the region. Light southwest wind shifting northwest over the day. Alpine high temperatures around -5. Freezing level 1800 m.
Monday: Sunny. Light to moderate northwest wind. Alpine high temperatures around -1. Freezing level 2100 m.
Tuesday: Sunny. Light to moderate south wind. Alpine high temperatures around -1. Freezing level 2300 m.
Cornices have been reactive to explosives, but have not been observed to trigger slabs on slopes below. A natural size 3 was reported on Thursday in the Dogtooth range. It was on a southeast aspect in the alpine and is suspected to have solar-triggered and run on the crust buried in mid-March.
Reports from Wednesday included small (size 1) wet loose point releases from steep solar aspects and explosive triggered wind slabs on north to east facing ridgetops.
Surface melt-freeze crusts exist on solar aspects and below about 2000 metres. Above this elevation, 15-40 cm of recent snow has otherwise seen some redistribution by southwest to northwest wind, and seems to be bonding well with underlying surfaces.
A widespread crust layer from the mid-March warm spell can be found 30-60 cm deep, and small surface hoar has been observed at this depth on some isolated north-facing slopes. Reports suggest the snow is generally well bonded to these layers but isolated instances of large solar-triggered slab avalanches running on the crust have been observed. Deeper layers are strong and have been unreactive over the past few weeks.
