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RegisterApr 9th, 2019–Apr 10th, 2019
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More snow than rain will come during the day Wednesday with cooler temperatures and strong southwesterly winds. Use caution at upper elevations around recently wind loaded slopes 35 degrees and steeper. Wet loose avalanches could occur within new snow by the afternoon.
In the past 24 hours, the Heather Meadows weather station reported .50in of water, bringing the total water we have received in the past week up to 4.5in. This precipitation has come as almost all rain below 4000ft causing our low elevation snowpack to quickly disappear. Between 4000-5500ft, about 1ft of wet snow accumulated this past weekend, but was rained on and then re-froze Monday and Tuesday making for nasty travel conditions. Above 5500ft, winter is hanging on with deep drifts of dry snow and blustery conditions.
The coolest temperatures we have seen in several days are expected Wednesday, with snow levels set for 3000ft and another .50-.75in of water arriving during the day. Expect a refresh of new snow near and above treeline and increasing avalanche danger as the snow accumulates throughout the day. Strong WSW winds will drift the new snow into shallow wind slabs, and thicken older wind slabs that formed over the weekend.
The only avalanche activity in the past week has been isolated and small loose wet slides (D1) on slopes 40 degrees and steeper. Poor visibility has limited observations above treeline where uncertainty exists regarding the sensitivity of the wind slab problem. Keep in mind that melting cornices, widening glide cracks, and opening creeks continue to pose a hazard during this spring transition. Give these a wide berth and be heads up as the recent snow may hide these and other obstacles.
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:
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
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