Avalanche Forecast Snoqualmie Pass
Wednesday 30th January 2019
Forecaster: Dallas Glass
The Bottom Line: Mild temperatures and a little sunshine will continue the weather pattern we’ve been experiencing for the past week. You may not see the snow surface soften, except in areas where you find fewer clouds. The greatest hazard you face may come from difficult travel conditions such as icy slopes and breakable crust.
Snow and Avalanche Discussion
Multiple freezing levels Thursday, with a slight return of the east flow, may keep you changing layers as you travel. Despite the differences in temperature, there won’t be enough change in the weather to increase the avalanche danger. If the sun comes out, you may see the snow on southerly slope soften. If you find wet snow deeper than your ankle, it’s time to change to less sun effected slopes. Thursday will be the last quiet day of this high-pressure pattern. Today’s surface is tomorrow’s interface. Do you see weak snow that may get buried during this next storm? This is your chance to track the weak snow while it's still on the surface.
Difficult travel conditions may pose the greatest risk to backcountry travelers Thursday. You may encounter very firm, icy surfaces, breakable crust, or old wind-blown snow as you travel.
Thu 31st Jan 14:26 - Dennis D'Amico
Weather Synopsis for Thursday night through Saturday
An approaching frontal system has blanketed the north and central Cascades in a high overcast this afternoon. Areas further south will begin to fill in tonight as the system approaches the coast.
Precipitation should begin for the Olympics and Mt. Baker area later this evening, but precipitation won't make much progress inland as the front becomes more north-south oriented and slows. Locally moderate to even heavy precipitation is expected in the Mt. Baker area on Friday, with a secondary bullseye for the Paradise/Crystal area.
Snow levels will lower late tonight but won't cool further until the front slowly kicks east of the Cascades Friday night. Snow levels look rather unimpressive (mild) with this system. Easterly flow may initially drag down snow levels to 4000-4500 feet for Stevens and Snoqualmie early Friday morning, but snow levels are expected to quickly settle above all the major Pass levels on Friday.
The frontal boundary will split and shear as it passes inland Friday evening with showers quickly diminishing toward Saturday morning. The Pacific Northwest will be in the weather equivalent of no man's land on Saturday with westerly (zonal) flow over the area and storm systems located to our north and south. Snow/freezing levels for the Cascades will stay constant on Saturday in the 4000-5000 ft range.
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.