Avalanche Forecast

Archived

Jan 20th, 2015–Jan 21st, 2015

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Mt Hood.

If travelling into the near and above treeline elevation bands Wednesday, watch for lingering wind slab on lee aspects and loose wet avalanches on solar aspects.

Detailed Forecast

Freezing levels on Wednesday should continue the gradual rising trend that began on Tuesday. Increasing high and mid clouds should be seen in the afternoon.

Recent shallow storm snow should continue to settle, but filtered sunshine and increasing temperatures may activate loose wet avalanches predominately on steeper southerly slopes near and above treeline. There likely isn't enough snow on southerly aspects near and below treeline for significant wet loose danger.

Also, there may be pockets of sensitive wind slab mainly on N-SE aspects near and above treeline.

Snowpack Discussion

Strong southwest flow carried a warm and wet front across the PNW Saturday night. This front tapped subtropical moisture pushed snow levels pretty high on Mt. Hood and resulted in 3.5 - 4.5 inches of rain at NWAC sites. A cooling trend Sunday along with another inch of water ended as 4-5 inches of new snow between 5-6000 feet by Monday morning.

Mt. Hood pro-patrol reported wind transport Sunday night and Mon AM leading to a thin wind slab above treeline producing small but regular releases during control work on lee slopes around 7000 ft. West winds eased off more quickly than forecast Monday and new wind transport was likely insignificant. They also reported the storm snow was well bonded to the most recent rain crust.

Light winds and slowly rising freezing levels on Tuesday should have helped further stabilize the upper snowpack.

The mid and lower snowpack at Mt Hood should also mainly consist of melt-freeze crusts and stabilized rounded grain layers from warm stretches so far this winter.

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.