Bulletin d’avalanche

Mt Hood

Mar 22 – 23, 2019Northwest Avalanche Center
Voir sur la carte
Archivé · expiré 8 years ago

Danger d’avalanche

Sun
Alpin
1 · Faible
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
Ouvrir la carte complète

Points saillants

A change in the weather to cooler and cloudier conditions has dramatically lowered the wet snow hazard. Continue to avoid very steep slopes that have wet snow deeper than your ankle where you can trigger a small but powerful loose wet avalanche.

Problèmes avalancheux

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1

    Cooler weather and mostly cloudy skies will limit the loose wet hazard on Saturday. Continue to be suspicious of very steep slopes that don’t see a firm refreeze Friday night.

    Monitor the surface snow and change your aspect and move to lower angled terrain if find wet surface snow deeper than 6”. Be especially cognizant of the consequences of even a small avalanche around terrain traps like gullies or cliff bands.

    We haven’t had any reports of Wet Slab avalanches in several days. The lack of observed slab avalanches plus the cooling have allowed us to remove Wet Slab from the problem list. If you see evidence of new wet slab avalanches, dial back your terrain use immediately to deal with the uncertainty surrounding this dangerous and hard to predict avalanche problem.

    Despite the cooler weather, avoid traveling on cornices as they often break back further than you anticipate. Limit your exposure if traveling on slopes below large overhanging cornices.

Discussion

After a week of widespread above freezing temperatures and a wet snow avalanche cycle that likely peaked last Sunday-Tuesday, we have turned the corner toward more typical cooler/showery spring-time weather. After a mild and sunny start to Friday, clouds moved in during the afternoon and light snow began falling.

New snowfall amounts Friday night are forecast to be light (2-4") and temperatures above treeline should cool and remain below freezing. This should help limit the loose wet potential to very steep solar (E-S-W) aspects near and below treeline.

If more new snow accumulates than forecast Friday night, anticipate a greater loose wet hazard and plan to avoid all steep sunny slopes in the afternoon.

Snowpack Discussion

March 22nd, 2019

Enter Spring

If you’ve been in the snow recently, the wintery conditions of early March may seem worlds away. You may be in for a surprise if it’s been a while since you were in the mountains. The weather has taken a turn towards spring in the last couple weeks and the Cascade snowpack the has undergone major changes. Unseasonably warm temperatures and strong sun followed a month-and-a-half of cold, winter storms. Mid-elevation weather stations stayed above freezing from March 15th-22nd with high temperatures reaching the upper 50’s to low 60’s. For an in-depth survey of the regional snowpack, we’ll divide the terrain up by aspect and elevation.

A graph showing temperatures between 4,000-5,000ft around the Cascades from the 16th-21st.

Aspects

Northerlies

Along with the warm temperatures, the spring sun has played a major role in warming snow surfaces. The result is a snowpack that varies by aspect. In most regions, shaded and northerly slopes remain relatively unchanged. Aside from some settlement and firmer or moist surfaces, the snow on north aspects is almost entirely dry. Even some low elevation north slopes are still holding snow.

Sunny slopes

The snowpack on east through south through west aspects is a different story. The strong March sun melted snow surfaces and drove melt-water into the snowpack. This is most dramatic on steep (over 35 degrees) southeast through southwest slopes below 5,000ft.  In some areas, you can find meltwater up to 3 feet below the snow surface with drainage channels well established. Between this warm period and rain events in the first half of the winter, the entire snowpack has transformed to melt forms. An important point to note is that as of the 22nd, these solar aspects remain unfrozen and weak. Cooler weather ahead may help strengthen moist to wet layers.

A glide avalanche (D2) released from a rock slab late on the 20th. Lichtenberg Mtn, 5,100ft, SE aspect. Other glide avalanches occurred on the 20th at Snoqualmie Pass and in Tumwater Canyon. Photo: Josh Hirshberg

Elevation

Low elevations

As you travel from low valleys to higher peaks, you’ll notice a major difference in the snowpack based on elevation. With all the low-elevation snow this winter, there are still some cold, shaded slopes holding pockets of snow down to 1,000ft, especially east of the Cascade Crest. However, most slopes below 3,000ft have lost much of their snow cover. Many low elevation, sun-exposed slopes are bare, especially in areas that previously held less than 3 feet of snow. The low elevation snowpack is no longer substantial enough to allow for easy travel over snow or widespread avalanches.

Loose wet avalanches on the south side of Table Mtn, near Mt Baker. 3/17. Photo: Pete Durr

Mid-elevations

At mid-elevations, around 3,000-5,000ft, the snowpack is still deep and layered. Many slopes at this elevation band near and west of the Cascade Crest are holding 6-10 feet of snow. This is also where you’ll find the most dramatic variation in the snowpack based on aspect.

High-elevations

Above 5,000ft you’ll encounter a snowpack similar to what you may have found around the 1st of March. Upper elevations have stayed mostly dry. The most sun-exposed slopes have surface crusts but have not seen much water or change to melt forms below the surface.

Régions couvertes