Avalanche forecast

Mt Hood

Apr 4 – 5, 2019Northwest Avalanche Center
View on map
Archived · expired 7 years ago

Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
Open full map

Highlights

The avalanche danger will peak late in the day as a series of storms bring snow and wind to Mt. Hood. Wind slabs will grow larger and more dangerous throughout the day. Steer away from wind-affected slopes greater than 35 degrees.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    An initial wave of precipitation will bring snow to areas above 6000 ft, with wind slabs building above this elevation. Wind slabs will increase throughout the day and peak in the afternoon as a second shortwave feature brings in moderate precipitation with moderate to strong winds in the afternoon. Wind slabs will build into the near treeline band and may become large at higher elevations. As the day wears on, choose more conservative terrain in wind-sheltered areas and avoid wind-loaded slopes greater than 35 degrees.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    While we think that the snowpack has transitioned enough to generally handle 1” of rain in 24 hours, there may be isolated exceptions to that rule. If you encounter wet snow and sink in deeper than your ankle, choose terrain less than 35 degrees.

Discussion

Snow and Avalanche Discussion

Mt. Hood could see an inch of water equivalent by the end of the day Friday and this will bring a drastic increase in slab avalanche danger. The new snow will force you to adjust your travel patterns that you’ve become used to during the recent spring diurnal cycle. It will also increase loose wet avalanche danger in steeper terrain below treeline.

Weather models are struggling with the shortwave features slated to arrive late Thursday night and late afternoon/evening on Friday. Thus, you will need to use your own observations to determine whether the avalanche conditions line up with the forecast. If they don’t, adjust your travel plans to choose more conservative and lower-elevation terrain.

Mt. Hood saw light rain and snow on Thursday with no snow at Mt. Hood base, but 3” of new at 6600 ft, drifting 4-5” in places. The new snow as bonding well and very stubborn to trigger. A larger storm system brought between 0.50" - 1.00" of precipitation to Mt. Hood Tuesday night and Wednesday. Unfortunately, most of this fell in liquid form below 6500'-6000'. Above this elevation, several inches of snow fell.

Snow cover below 4000' is disappearing quickly and south facing terrain near ridgelines are melting out as well. The mountains are still experiencing their spring transition. Creeks are opening up with snow bridges collapsing. Glide cracks are evident and may release in generally predictable locations, but without warning. Sagging cornices may fail when stressed by the warmth of the sunshine or the weight of a person. Use caution if you travel near these features.

Snowpack Discussion

April 3rd, 2019

Spring snowmelt

The snowpack in much of the Cascades has changed dramatically in the past two weeks. The weather has shifted solidly to spring-like patterns. The spring warm-up started in mid-March with a prolonged period of relatively clear skies and warm temperatures. Moving into April, we’re seeing periods of unsettled spring weather bringing rain to many low and mid-elevation slopes and snow to upper elevations.

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

Since the peak height of snow in mid to late February, mountain weather stations in the 4,000-5,000ft range show an average of 27% decrease in height of snow. Looking at weather stations in nearly every zone, the percentage decrease ranged from 22-29%. This year's spring snowmelt is much earlier than normal. 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.

NWAC climatological snow depth data from April 1st. You can view it on our website here.

Spring avalanche considerations

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

  1. Is there any recent snow accumulation that could cause avalanches? If so, what kind of avalanches could you trigger? And where?

  2. What are the high and low temperatures of the past 24 hours as well as the forecasted temperatures during the time you’ll be in the mountains? Could these create weak, wet snow surfaces?

  3. 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?

Glide avalanches and holes opening up in rocky terrain near Mount Herman. Photo: Andrew Kiefer

Other considerations

In addition to daily avalanche hazard, the early snowmelt is creating some 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.

We are approaching the end of our daily avalanche forecasting season. The mountain weather forecast will continue into the spring, and the weather station data is available year round. Keep checking the forecast for conditions updates on the end of season information.

Regions covered