Avalanche Forecast

Archived

Apr 23rd, 2014–Apr 24th, 2014

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Regions

Olympics.

Dangerous avalanche conditions at Hurricane and from Mt Baker to Snoqualmie on Thursday. Careful snowpack evaluation, cautious routefinding and conservative decisions should be essential.

Detailed Forecast

A warm front will move across the Northwest on Wednesday night followed by the cold front Thursday morning. This will cause southwest winds and further moderate to heavy rain and snow especially from Mt Rainier to Mt Hood. Snow levels should rise to the 4000 foot, 5000 foot and 6000 foot range in the north, central and south Cascades respectively on Wednesday night. Snowfall in the ATL and NTL zones for the 48 hours ending Thursday morning should be in the .5-1 foot range from Mt Baker to Snoqualmie and in the 2-3 foot range from Mt Rainier to Mt Hood. Less snowfall is likely east of the crest.

Southwest winds and moderate to heavy showers should be seen following the front on Thursday morning. Further southwest winds and generally moderate showers should be seen Thursday afternoon. Snow levels should lower a bit to about 4000 feet in the north and 5000 feet in the south following the cold front.

New snow will be very susceptible to strong spring solar effects and strong daytime warming! New or further building storm and wind slab will also be seen. These avalanche concerns will be especially where snowfall is expected to be heaviest from Mt Rainier to Mt Hood.

The avalanche concerns will be listed as very likely from Mt Rainier to Mt Hood, likely at Hurricane and from Mt Baker to Snoqualmie, and possible east of the crest.

Snowpack Discussion

It might be late April but Mother Nature isn't watching the calendar and more weather systems are moving across the Northwest this week.

Recent reports are few and far between. Yesterday the Chinook Pass DOT crew reported large natural and triggered wet loose avalanches on solar aspects. Wednesday morning Mt Hood Meadows ski patrol reported widespread triggered 6-10 inch storm slab avalanches. This afternoon the Mt Hood Meadows ski patrol reports widespread natural and triggered wet loose avalanches in their closed Heather Canyon area.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.