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Avalanche Forecast

Archived

Apr 10th, 2017–Apr 11th, 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.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Lizard-Flathead.

The sun packs a punch these days - avoid south facing slopes on Tuesday if the sun comes out in full force. Limit your exposure to cornices when it's cloudy and completely avoid them when it's sunny.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Some sunny breaks are expected on Tuesday, and then we're back to unsettled weather for the remainder of the forecast period. TUESDAY: Flurries Monday overnight (5-10cm possible) and then cloudy with sunny periods on Tuesday. Light southerly ridgetop winds. Freezing level around 1800 m.WEDNESDAY: Flurries late morning into the afternoon (5-10cm). Moderate easterly ridgetop winds. Freezing level around 1700 m.THURSDAY: Snow continues Wednesday overnight with 10-25cm possible by Thursday afternoon. Moderate southwest ridgetop winds. Freezing level around 1700 m.

Avalanche Summary

On Monday, several storm slabs and cornice triggered slabs to Size 2.0 were reported on northerly aspects between 1750m and 2100m. Some small, loose wet avalanches to Size 1.5 were reported on south facing aspects near 1750m in the afternoon on Monday.

Snowpack Summary

Since Saturday morning, 10-25 cm of new snow has fallen at treeline and above. The sun on Monday made snow surfaces moist and should stabilize quickly after an overnight refreeze. This new snow sits on a very hard crust up to 1400m (on north aspects) and up to 1700m (on south aspects).Moderate southwesterly winds have created wind slabs on lee features below alpine ridgetops. Cornices are large, looming, and best avoided.The snowpack is well settled and continues to transition into a spring snowpack, becoming isothermal at treeline in some areas and below treeline in most areas.The December facets and November rain crust are buried deep, but these deep persistent weaknesses have not been reactive for several weeks. That said, rapid warming of the snowpack or a large trigger, like a cornice, could trigger this layer.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.