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Avalanche Forecast

Archived

Feb 9th, 2017–Feb 10th, 2017

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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.

A mixed bag of avalanche problems should be expected on Thursday. Back country travel in avalanche terrain is not recommended through Thursday morning.

Detailed Forecast

A strong wet warm front will lift north over the Olympics and Cascades on Wednesday night to Thursday morning. Plan on rapid warming Wednesday night and heavy rain or snow with higher snow levels through Thursday morning. This should cause an avalanche cycle in the Olympics and Cascades which should test the snowpack. Small avalanches may step to deeper layers during the cycle.

A mixed bag of avalanche problems should expected on Thursday at Mt Hood. Loose wet avalanche will be listed as very likely for the period to Thursday morning. New wind slab should be seen in the above treeline by end of the daylight hours.Back country travel in avalanche terrain is not recommended through Thursday morning.

Wet slab avalanches and cornice failures should also be likely in areas with heavy rain Wednesday night to Thursday morning.

The cold front should cross the Cascades Thursday late morning or midday. This should cause a change to showers and lowering snow levels. The avalanche danger should begin to decrease following the cold front Thursday afternoon.

  

Snowpack Discussion

Weather and Snowpack

A strong storm cycle was seen Friday through Monday with about 3-4 feet of snow recorded at the NWAC Mt Hood stations. Temperatures were mild through the weekend with strong southwest winds followed by cooling and lighter winds on Monday.

Light snowfall was seen at Mt Hood on Tuesday, depositing about 2-3 inches of new snow with fairly light winds. 

Recent Observations

The Meadows pro-patrol had a busy day on Saturday with sensitive but generally shallow storm slabs easily releasing during control on a density change in the storm snow. Wind loaded NE slopes between 5500-6500 feet ran well during control work with crowns locally up to 2 feet.  

On Sunday morning the Meadows pro-patrol found storm slabs on all aspects of about 1 foot that were especially sensitive below treeline. E-NE aspects were being continuously loaded near and above treeline throughout the day. 

By Tuesday, reports of settling storm snow made avalanche control work less exciting, as avalanches were very limited to isolated wind loaded pockets. This is a good indication of improving conditions, at least for Tuesday!

The Meadows pro-patrol closed their gates by midday Wednesday due to deteriorating weather. Ski tests were beginning to produce small loose wet avalanches. Cornices were reported to be large after the last storm cycle.

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.

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.