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Avalanche Forecast

Archived

Feb 16th, 2017–Feb 17th, 2017

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

Regions

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Fresh wind and storm slabs may be poorly bonded to the old snow surface or crust layer. Caution in steep open terrain near and above treeline. Watch for wet snow conditions at lower elevations.

Detailed Forecast

A continued cooling trend is expected Friday with diminishing winds and a few light snow showers possible. This should allow recent wind and storm slabs to slowly settle and improve in higher elevation terrain. The cooling should allow for wet snow at lower elevations to begin re-freezing and strengthening. 

Watch for any wet snow conditions at lower elevations, especially on steep unsupported terrain features.

Avoid steep wind loaded terrain Friday, mainly below ridges, near and above treeline. 

 

Snowpack Discussion

Weather and Snowpack

The 2/8 - 2/10 storm cycle deposited 2-3 feet of snow in the Washington Pass area. In the central-east and southeast zones a rain crust formed with shallow amounts of new snow following at the tail end of the cycle. This storm cycle was a great test for any Persistent Weak Layers buried deeper in the snowpack. There was no evidence of any deeper releases and as a result, we have removed Persistent Slab from the problem list.

High pressure Saturday to Tuesday brought increasing sunshine and warming temperatures. Temperatures reached the 30's and 40's in many areas along the Cascade east slopes. This caused snowpack settlement, some small loose wet avalanche activity and a decreasing avalanche danger.

Another atmospheric river impacted the PNW beginning on Wednesday.  Light to moderate snow with warmer temperatures and some high snow levels occurred along the east slopes of the Cascades with localized freezing rain along the lower east slopes. Above freezing temperatures occurred during precipitation with light rain likely in the southeast zone up to 7000 feet, 5000-6000 feet in the central-east and reports from the north-east zone of a thin freezing-rain crust to near treeline elevations at least. 

Recent Observations

North

A report via the NWAC Observations page indicates a shallow climax slab avalanche on a north slope on Mt Patterson near Winthrop on Sunday. There is likely to be shallow faceted snow in this low elevation area.

NWAC observer Jeff Ward was out Thursday, 2/16 and reported the recent about 10 inches of  moist storm snow was being transported and building wind slabs through the day. There was evidence of a few natural wind slab releases and a natural storm slab was noted releasing sometime Thursday. A thin freezing rain crust formed mid-storm cycle and was yet to form a good bond as of Thursday.  

Central

NWAC's Tom Curtis travelled in the Icicle Creek area near Cashmere Mountain Saturday 2/11. Tom did not get far as there was only a dusting of recent snow over a slick, firm crust. The greatest danger in this area was from uncontrolled falls on the slick crust as opposed to avalanches. 

Another report via the NWAC Observations page for Dirty Face Peak for Sunday indicates that wind slab was unreactive there on Sunday.

Reports from the Mission Ridge pro-patrol mostly indicate a breakable surface crust from late last week and poor ski conditions Sunday and Monday.

Thursday afternoon 2/16, warm temperatures had reached the lower east slopes and numerous wet snow avalanches had released, including in Tumwater Canyon.

South

No recent observations. 

Problems

Wet Slabs

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.

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.