You may be able to trigger lingering small loose wet avalanches on steep slopes or small wind slabs on Wednesday. Minor amounts of moisture will spill over into the East South zone Wednesday afternoon. Watch for low snow coverage and weak, wet snow below 5000 ft with open creeks and exposed rocks.
Snow and Avalanche Discussion
We think that most of the snow fell near and west of the Cascade Crest on Tuesday, with little spillover and we think Wednesday will generally repeat that scenario with a slight chance to build very shallow wind slabs at upper elevations near the Cascade Crest.
In locations that did see fresh snow on Tuesday, you can trigger small loose wet avalanches in the recent snow on steep slopes. If the sun comes out, you may see natural avalanches on sun-exposed slopes. Most loose wet avalanches will be small and predictable, involving only surface snow. Look for soft, moist surface snow and use small test slopes to check the bond of recent snow. Stop and regroup in safer areas, out from under slopes that are being traveled on. If you find wet, unsupportive snow, avoid
Avoid triggering a wet loose avalanche near a terrain trap such as cliff bands, open creeks, exposed or barely covered rocks and trees, etc, that would amplify the consequences of even a small wet loose avalanche. On many southerly aspects, the new snow will be covering previously bare ground. If you find wet snow deeper than your ankle, make the easy call to stick to lower angled terrain.
Be sure to consider all the hazards that come with spring in the mountains. Factor in a good margin for error as hard to predict events like cornice fall, glide avalanches, icefall, rockfall, and a general “shed cycle.” When surfaces freeze and become firm, bring the right equipment to mitigate the hazard of sliding down icy slopes.
Forecast Schedule and No Rating
At this time, we do not have enough specific snowpack information to issue an avalanche hazard rating for the East Slopes South zone. However, even when No Rating is applied, applicable avalanche conditions and backcountry travel advice will be provided throughout the season. When weather systems produce very dangerous avalanche conditions in adjacent zones, NWAC will issue an avalanche warning for this zone as well.
April 9th, 2019
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
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:
Can you trigger avalanches due to new snow?
If so, would they be storm slabs or wind slabs? And where?
Can you trigger avalanches due to warming or rain?
Will recent snow be warmed enough to result in loose wet avalanches?
Will these avalanches be predictable point releases or more destructive wet slabs or gouging loose wet avalanches?
What are the recent high and low temperatures and the forecasted temperatures during the time you’ll be in the mountains?
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
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