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Avalanche Forecast

Archived

Dec 29th, 2014–Dec 30th, 2014

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Mt Hood.

More caution will be needed Monday at Mt Hood than the rest of the NWAC forecast area due to the heavy snowfall through Sunday.

Detailed Forecast

Northwest winds should change to northeast with an end to light snow showers and cool temperatures at Mt Hood on Monday. A stabilizing trend will start on Monday. But it will take longer at Mt Hood than the rest of the NWAC forecast area due to the heavy snowfall through Sunday.

Areas of lingering deep wind slab should be likely at Mt Hood on Monday. Watch for firmer wind transported snow on steep lee slopes.

Areas of lingering storm slab should also be possible on Monday. This could be pretty widespread at Mt Hood since most of Mt Hood received prolonged heavy snowfall.

Any hoar frost that survived the storm could increase the instability of wind or storm slab layers.

Instability should be limited to new snow and deeper instabilities in the snow pack are not currently expected at Mt Hood.

The sun should be out by later Monday but sun effects should be limited since we are barely past the solstice.

Note that northeast winds may increase Monday night and Tuesday so heads up for new wind slab potential on Tuesday.

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Snowpack Discussion

A cooler period with little precipitation was seen about Thursday to Friday. Some hoar frost is possible from Thursday night.

A cold front moved over the Northwest on Saturday and Saturday night. West winds changed to northwest, with moderate to heavy snow persisting at Mt Hood through today and a cooling trend. It has been dumping snow at Mt Hood today. NWAC sites at Timberline and Meadows indicate 1.5 feet of storm snow by this afternoon with at least a few more inches likely this evening and night.

NWAC observer CJ Svela called from Timberline to report heavy snow and heavy snow loading on this morning. The avalanche forecast for Mt Hood was changed to high for the above and near tree line zones.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.