Avalanche Forecast

The upper ridge and warm air mass should further build over the US west coast on Sunday. This should cause light winds and mostly sunny weather in the Olympics and Cascades with further warming temperatures.

Sun and heat effects should be the main factors to consider on Sunday. From a couple of observations it seems like surface snow was probably pretty solidly refrozen in most areas on Saturday morning. But the refreeze may more limited Sunday morning due to warmer weather. If so then surface snow could get a better start on being available for loose wet snow avalanches.

Loose wet avalanches should remain possible Sunday on steeper slopes involving the recent snow. Watch for wet surface snow getting deeper than your boot tops. Triggered loose wet avalanches should be most likely on steep solar slopes but could be seen on any steep aspect in this warm weather. Avoid areas below steep gullies and run out zones that might be prone to natural loose wet avalanches.

The potential for cornice releases may increase through the warm weekend. Cornice releases are basically unpredictable so avoid areas below cornices and remember that cornices can break much further back than expected along ridges.

Although not listed as an avalanche problem, powerful glide avalanches can release unexpectedly so also avoid areas below steep unsupported slopes or rock faces especially if they are showing glide cracks. Glide cracks may be hidden by the recent snowfall.

Storm and winds slabs will not be listed as avalanche problems along the west slopes due to reports of good bonds of the recent snow to the 4/12 crust and fast stabilizing rates seen at this time of year. However, be aware of the potential for isolated slab avalanche layers involving the recent snow mainly on non-solar aspects of very high terrain.

Weather and Snowpack

We've had two big warm-ups and spring shed cycles since the end of March. Over this time period the snowpack has undergone significant settlement with lower elevation snow beginning to fade away and with an overall transition to a spring snowpack.

A front crossed the Northwest Tuesday afternoon and night. Then a cool upper and surface low pressure system moved east along the Washington-Oregon border on Wednesday and Thursday. NWAC sites at Mt Hood had 11-14 inches of late season snow in the 3 days ending Friday morning with 6-8 inches of that snow in just the 24 hours ending Friday morning.

Storms in March continued to build unusually large cornices along many ridges. The potential for low probability/high consequence encounters, such as cornice failures and glide avalanches from steep unsupported slopes and smooth rock faces, should continue for awhile this spring. 

The mid and lower snowpack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

NWAC observer Laura Green was in the Heather, White and Mitchell Canyon areas in low visibility on Thursday 4/14. She found new building wind slab of 20-30 cm by late morning with shooting cracks on N-NE slopes at 6600 feet. Ski cuts were giving easy, small wind slab releases on slopes steeper than 30 degrees.

The Meadows pro-patrol gave the NWAC an extensive report for Friday 4/15. In the above treeline explosive control produced extensive wind slab releases on N-E slopes up to 4 feet deep running on the 4/12 crust. It was felt that these releases could have been triggered by skiers. In the near to above treeline they found ski triggered 4-6 inch wind slab also on N-E slopes but more limited in extent and some small ski triggered and natural loose wet avalanches on E-S slopes.

By Saturday the Meadows pro-patrol reported only some limited small loose wet avalanches in steep terrain. Ski conditions were bad off piste in about 5 inches of wet snow.