Avalanche Forecast Mt Hood

Date Issued: Valid Until:

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Avalanche Forecast

Wed Apr. 10th · 11:01AM

Alpine

Danger Ratings High

Treeline

Danger Ratings Considerable

Below Treeline

Danger Ratings Considerable
Wind Slabs Wind Slabs

Alpine

Danger Ratings High

Treeline

Danger Ratings Considerable

Below Treeline

Danger Ratings Considerable

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Very dangerous avalanche conditions continue to exist above treeline on Mt. Hood where very large wind slabs continue to release. These avalanches can travel multiple miles, thousands of feet of vertical, may destroy small trees, and avalanche paths that have already run may run again. During cycles like these, avoid all terrain where avalanches can start, stop, or run on Thursday!

Discussion

Snow and Avalanche Discussion

Very large avalanches continue to release off the slopes of Mt. Hood, daily! Mt. Hood will continue to receive heavy snow and moderate to strong wind transport continues to load already enormous wind slabs with westerly winds and intense snowfall. We expect that very large avalanches will continue to release and the same path may re-load and can run even farther the second time. It is not recommended to linger near the avalanche debris during a storm cycle.

Note that below treeline some locations may receive heavy wet snow that bonds firmly and securely without wind transport. In these locations, a considerable rating is driven by the hazard of very large avalanches descending from the alpine.

Here is some photographic evidence from the cycle:

Banana Hammock, Clarke Drainage, 04/10/19. HS-AA-D3-R3: Aspect ESE, 7400 ft. starting zone, ran an Unknown Distance. Crown Height estimated to be 2 X 10 ft step downs. Photo Credit: J.P. Bevilaqua

 

Super Bowl Slide, Clark Canyon, 04/09/19, HS-AA-D4-R4, ENE Aspect, 8800 ft. starting zone. Ran a total length of 14,157Ft., total Vertical of 3600 ft. Unknown Crown Size. Photo Credit: J.P. Bevilaqua

 

Basalts Slide, Heather Drainage, 04/09/19, HS-AA-D3.5-R4, E Aspect, 7500 ft staring zone.  Ran a total length of 5100Ft., total Vertical of 2000 ft. Unknown Crown Size. Photo Credit: J.P. Bevilaqua

At least two more very large natural avalanches released over the weekend or on Monday.

Snowpack Discussion

April 9th, 2019

Spring Conditions

The snowpack and weather have shifted solidly to spring-like conditions. A major warm-up started in mid-March with a prolonged period of strong sun and warm temperatures. This created a major difference between the snowpack on sunny slopes and that on shaded aspects. More recently, warm, wet, and sometimes weak spring storms have brought more rain than snow. The bulk of the precipitation with these storms focused on the southern forecast zones. Even so, mid-elevation rain established a dramatic snow line (about 4-4,500ft) below which the snowpack is minimal to non-existent in most zones. Going into the second week in April, intense snow and wind drove a prolonged period of High danger at Mt Hood.

A crown of a very large avalanche (D3+) above Mt. Hood Meadows resort. 04/08/2019. Photo Credit: Peter Moore.

Challenging Weather Forecasts

The Cascades have been experiencing unsettled spring weather with rain to many low and mid-elevation slopes and snow at upper elevations. Spring weather forecasts in the Cascades are notoriously challenging. With these storms, the weather models have been inconsistent and the accuracy has been limited to 12-24 hours, at best. A trend has been significant precipitation amounts for the Mount Hood area and other south-central Cascade volcanoes. 

Very bare southeast aspects of Rock Mtn/Nason Ridge. April 2nd. Photo: Josh Hirshberg

Shrinking Snowpack

From the peak height of snow in mid to late February through early April, mountain weather stations in the 4,000-5,000ft range showed an average of 27% decrease in height of snow. The percentage decrease ranged from 22-29%. This year's spring snowmelt is much earlier than normal. If you’re traveling in the mountains, the loss of snow coverage is most noticeable on southerly, sun-exposed slopes and below 4,000ft. On northerly aspects and slopes above 5,500ft, the snowpack has seen less dramatic changes and has even maintained some dry layers. On upper elevation shaded slopes there’s still potential for large wet slab avalanches with prolonged warm temperatures or high elevation rain events.

A natural loose wet avalanche (D1), Lichtenberg Mtn, N, 4,850ft. 4/7/2019. Photo: Will Govus

Spring avalanche considerations

As you head into the mountains there are a few questions to ask yourself common to spring avalanche conditions:

  1. Can you trigger avalanches due to new snow?

    1. If so, would they be storm slabs or wind slabs? And where?

  2. Can you trigger avalanches due to warming or rain?

    1. Will recent snow be warmed enough to result in loose wet avalanches?

    2. Will these avalanches be predictable point releases or more destructive wet slabs or gouging loose wet avalanches?

    3. What are the recent high and low temperatures and the forecasted temperatures during the time you’ll be in the mountains?

    4. How is the cloud cover contributing to the melting or freezing of surface snow? Did clear skies allow for a sufficient overnight freeze? Will the sun be strong enough to weaken surface layers?

Debris from a natural loose wet avalanche (D2), Lichtenberg Mtn, SW, 5,000ft. 4/7/2019. Photo: Josh Hirshberg

Other Considerations

In addition to daily avalanche hazard, the early snowmelt has created other travel considerations. Some roads and lower elevation slopes may not have enough continuous snow coverage for travel on snow machines. Holes melted around rocks, trees, and creeks could create a fall hazard. When nighttime temperatures and cloud cover allow for surface freezes, bring appropriate equipment to mitigate slip and fall hazard on steep slopes.

The last daily avalanche forecast for all zones will be issued for April 14th. Statewide mountain weather forecast and weekly avalanche condition advisories will continue through May. The weather station data is available year round. Keep checking the advisories and help us out by submitting observations when you are in the mountains.

Glide avalanches and holes opening up in rocky terrain on an east aspect of Mount Herman. 4/3/19 Photo: Andrew Kiefer

Problems

Wind Slabs

Wind Slabs

Continue to avoid all areas where avalanches can start, stop, and run from above treeline terrain on Mt. Hood. Strong winds and heavy snowfall will continue to produce very large, powerful that are releasing daily on the upper slopes of Mt. Hood and traveling into terrain in all elevation bands. Near treeline and below, wind-affected slopes may still be reactive. Avoid all open slopes greater than 35 degrees. Wind drifts and slopes stripped down to old crusts are indications of the degree of recent wind transport. Punchy snow and shooting cracks tell you that there is instability in your terrain.

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.

 

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..

 

Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.

 

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

very likely

Expected Size

1 - 2