Bollettino valanghe

Mt Hood

Jan 1 – 2, 2019Northwest Avalanche Center
Vedi sulla mappa
Archiviato · scaduto 8 years ago

Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
Apri la mappa completa

In sintesi

Recent wind slabs are becoming more difficult to trigger, however shifting winds have transported snow to a variety of slopes above treeline. You could still trigger a wind slab on steeper wind-loaded slopes, so continue to travel with caution at higher elevations. In exposed terrain, recent snow may be stripped to a strong rain crust.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1

    Wind slabs formed over the weekend are gaining strength, becoming more difficult to trigger. Backcountry travelers and local professionals reported finding wind slabs in unusual locations due to shifting wind directions. You may still trigger wind slabs on convex rollovers, near the sides of cross-loaded gullies, and on wind drifted snow below ridgelines. These wind slabs have formed over a very strong freezing rain crust formed last Saturday to at least 7300 ft. 

Discussion

Avalanche and Snowpack Discussion

Following rain and freezing rain Saturday, 10-12 inches of snow accumulated Saturday night and Sunday with strong WNW winds. Winds shifted to easterly and transported snow to a variety of aspects making wind slabs possible on all aspects. Mt. Hood Pro-patrol found fresh but stubborn wind slabs up to 2' deep near treeline. More importantly, wind slabs had developed on unusual aspects, cross-loaded slopes and formed on open slopes below treeline. Winds had scoured ridges to the most recent firm icy crust in many areas. We have no recent observations from above treeline due to the recent stormy conditions. 

Snowpack Discussion

December of 2018 was fun (from a forecasting perspective) with three pronounced avalanche cycles, a couple different persistent weak layers, some rain events, and a flurry of human triggered avalanches to ring in the New Year. Most importantly, it seems that we made it through the last days of 2018 without anyone getting seriously hurt by an avalanche.

The deep (Dec 9) layer responsible for many of the avalanches early in the month no longer seems to be a problem in the western zones. That said, it is still possible to trigger an avalanche on its counterpart (or basal facets) in the eastern areas.

A widespread layer of surface hoar formed around Christmas. Late December storms preserved this layer in areas above the rain line and we have numerous (more than a dozen) reports of people triggering avalanches on it in the last three days. At least 4 people were caught and carried during this period, but so far we have no reports of serious injury. Most of these avalanches were soft slabs, D1-D2+, but there were several harder wind slabs in the mix.

It appears that the layer is most reactive and/or prevalent in the Crystal Mountain backcountry and in the mountains around Leavenworth and west of Mazama.

Surface Hoar can be an especially tricky and persistent weak layer. Read more about it here.

Regioni coperte