The Bottom Line: High freezing levels, light winds, and sunshine are likely to soften snow on steeper, sunny slopes, but multiple crust layers near the top of the snowpack should limit the potential for Loose Wet avalanche activity. Depending on your aspect and timing, you may encounter difficult travel with slide for life conditions a possibility.
Snow and Avalanche Discussion
A thick, supportable ice crust exists on all elevations and aspects and broke down on Saturday and Sunday with very warm temperatures and sunshine, however a cool east wind limited surface melt on Monday. Winds decreased on Tuesday and 1-5” of melted snow developed on southerly slopes steeper than 20 degrees, creating pleasant riding conditions. The depth of the melt was limited by additional crusts in the snowpack, limiting avalanche concern. We expect similar conditions to play out again on Wednesday with warm temperatures, sunny skies, and light winds in the forecast once again.
However, if you do find wet snow deeper than your ankles or roller ball activity, adjust your aspect to find safer, firmer snow. Elsewhere, hard surface crusts make for hazardous conditions from uncontrolled falls. These fall and slide conditions should continue Wednesday so use caution when traversing steep slopes with consequences below.
Recent cornices have been evident in the terrain. You are most likely to find them overhanging northerly slopes or on the edge of gully features. Don’t linger below these cornices on Wednesday as the sun begins to warm them.
Wed 30th Jan 14:19 - Dennis D'Amico
Weather Synopsis for Wednesday night through Friday
Upper level ridging positioned upstream of the PNW will keep the fair weather going through Thursday. High and mid clouds streaming overhead in NW flow aloft should remain mostly focused from Stevens Pass to the Canadian border through tomorrow with clearer skies expected for the south Washington Cascades and Mt. Hood area.
Temperature inversions will remain in place in the Cascade Passes due to cool and light east flow and also along the east slopes of the Cascades, with much colder air sitting along the lower slopes and valleys. Mild temperatures in the 40s and even a few 50s will continue through tomorrow for higher elevation stations and the general south Washington Cascades and Mt. Hood area.
An approaching weather system will start to lower the freezing level gradually Thursday afternoon with precipitation beginning early in the evening for the north Cascades and Olympics. The front will begin to stand up and become more north-south oriented as a new low pressure system develops along the frontal boundary off the California coast Thursday night. This will slow the onset of precipitation for the south and central Cascades. Snow levels won't lower enough with this system to keep rain out of the forecast for lower elevation sites. Easterly flow through the Passes is not expected to play a significant role in precipitation type.
Tue 29th Jan 09:00
January, 29, 2019
Well, here we are towards the end of January and deep into a week-long high pressure ridge. The snowpack survived extremely warm temperatures and sunny skies over the weekend with minimal new wet avalanche activity reported. This break in the weather allowed for avalanche danger to steadily decline in all regions. At this moment, avalanche hazard is limited in all zones.
We’ve been hearing a variety of tales from backcountry travelers over the past week. We’ve heard reports of extremely firm slopes creating slide-for-life conditions. Others reported perfect spring like snow. Some encountered difficult breakable crust. And, for a lucky few, softer, drier, mid-winter snow has been found.
So, what do we make of all this? Well, we can use a few ideas to sum up the current state of the snowpack. I’d like to call it: North, South, East, West.
While a high elevation rain event, towards the end of the last storm, formed surface crust in many regions, it’s the constant melt-freeze cycles from the past week, that caused a divergence in the Northerly and Southerly snowpacks.
South: On sunny aspects, the sun drove warming and melting of surface snow. Most days, the snow surface softened on steep, southerly slopes receiving direct sunshine. Long, cool, winter nights allowed for the surface to freeze again. This repeating melt-freeze pattern created a thicker, firmer, and more supportable surface. Any weak surface snow, such as near surface facets or surface hoar, melted during the day limiting its development. For the fortunate, well timed travelers, this cycle resulted in some great spring like snow conditions. For those unfortunate enough to be traveling too early in the day, or on days where clouds and cooler temperatures delayed the snow surface thawing, very firm travel conditions were encountered.
North: On shady slopes, things haven’t exactly been soft. The crust formed at the end of the last storm extends to high elevations (Mt. Hood 7000+ft, South Cascades 6500 ft, Passes and Central Cascades 6000 ft. and West-North 5500 ft.). Only areas in the East Cascades seemed to escape the wrath of this breakable crust. Without the help of the sun, shady slopes haven’t been softening even during this period of warm weather. Instead, the surface crust underwent some weakening. Observations found faceting on top of and below this crust. In some locations, this caused the crust to begin to degrade, becoming less supportive. NSFs Jan 28 2019.jpg tell, but this is a good time to get out and see where those potential weak layers exist.
It’s not uncommon for our east-side forecast zones to experience lingering persistent weak layers (PWL’s). This season, we’ve also seen several different PWL’s in our western zones. By in large, this break in the weather gave the snowpack time to gain strength in all zones.
West: While you may find some weak snow in the upper few inches of the snowpack, the mid and lower snowpack has been found to be quite strong. Firm rounded grains, stout crust, and strong frozen melt-forms make up the majority of the snowpack at this time.
East: The east-side snowpack continues to be highly variable. You may find deep strong snowpacks closer to the crest or you could encounter shallow weak snowpacks areas further east. While there are number of potentially weak interfaces, there are two more common layers we’ve got our eyes on.
- January 22nd surface hoar and small facets. You can find these just under the recent storm snow, about a foot down. .
- December 26th surface hoar. This layer can be found from 16” to 40” down and is still producing clean, planar shears with tests.
You are most likely to find these layers to be preserved on wind sheltered, shady, and open slopes above 5,500ft. These layers are likely to be more reactive further east, where the snowpack is less than 4 feet deep and variable especially east of highway 97. What’s the future of these buried PWL’s? How long will they hang around? Often, persistent weak layers go “dormant” during periods of high pressure such as this. They may or may not become reactive with the next storm. It’s tough to say at this point. We’ll have to keep tracking them and gaining information to round out our understanding of these layers.
Weather forecasts suggest that this high pressure ridge is coming to an end later this week. As the weather changes, expect avalanche conditions to change too. Make sure to check the forecast if you are planning on getting out this weekend.