Avalanche Forecast
Dec 19th, 2018–Dec 21st, 2018
Alpine
3:
Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2:
Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2:
Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3:
Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2:
Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2:
Moderate
The avalanche danger rating below treeline will be moderate
Regions: Stevens Pass.
The Bottom Line: New snow, strong winds, and warming temperatures will increase your chances of triggering an avalanche on any open slope greater than 35 degrees. Older weak snow still exists deep in the snowpack. You may trigger very large and deep avalanches from thinner spots in the snowpack or with larger triggers.
Snow and Avalanche Discussion
Our hydrologic winter began in earnest on December 9th, when the storm track started pointing at the Pacific Northwest. The first week in December, little snow was on the ground, but temperatures were cold and the skies were clear. This formed a layer of surface hoar and/or facets on the surface of our then shallow snowpack. This is widespread throughout the Cascades. Nearly continuous storms have amounted to approximately 5 feet of snow over the top of this layer in the Stevens Pass area. Recent avalanches have failed on this layer at Crystal Mountain, where a natural cycle and controlled releases were observed. On December 18th, a ski patroller was caught and carried, but remarkably sustained very little injuries. The avalanche was large relative to the path, and large enough to bury several buildings. It occurred on a Northwest aspect at 6600ft.
Regional Synopsis
Why has the avalanche danger been so high for so long? Two reasons: A very active and wet weather pattern and widespread persistent weak layer.
For perspective, the approximate snow totals from 12/9-12/18 are:
In many areas, a layer of buried surface hoar and/or weak sugary facets was buried on December 9th. This layer has been the cause in numerous natural, explosive, and skier triggered avalanches. As this layer gets deeper it gets harder to assess … in short, the scenario is tricky and getting more dangerous by the day.
Higher snow totals along the Hwy 542 corridor /Mt Baker area have driven several avalanche cycles during this period. Loading from recent storms has been more incremental to the east and south and we have not yet experienced a widespread cycle …
When will we reach the breaking point? It’s hard to say. What we do know is we have a deep weak layer, reports of very large explosives triggered slides at Mission Ridge and Crystal Mountain, and more storms on the way.
Be patient and continue to stick to lower angle slopes with nothing above you. This is a good time to avoid areas where avalanches can start, run, and stop.
We’d like to thank all of you who have sent NWAC your observations. If you are out in the mountains, let us know what you see.
For perspective, the approximate snow totals from 12/9-12/18 are:
- Mt Baker: 102â€
- Washington Pass: 55â€
- Stevens Pass: 76†mid-mountain
- Snoqualmie Pass: 68†mid-mountain
- Crystal Mountain 70†Green Valley
- Paradise: 78â€
- Mt Hood Meadows: 44†mid-mountain
- Olympics: 48â€
In many areas, a layer of buried surface hoar and/or weak sugary facets was buried on December 9th. This layer has been the cause in numerous natural, explosive, and skier triggered avalanches. As this layer gets deeper it gets harder to assess … in short, the scenario is tricky and getting more dangerous by the day.
Higher snow totals along the Hwy 542 corridor /Mt Baker area have driven several avalanche cycles during this period. Loading from recent storms has been more incremental to the east and south and we have not yet experienced a widespread cycle …
When will we reach the breaking point? It’s hard to say. What we do know is we have a deep weak layer, reports of very large explosives triggered slides at Mission Ridge and Crystal Mountain, and more storms on the way.
Be patient and continue to stick to lower angle slopes with nothing above you. This is a good time to avoid areas where avalanches can start, run, and stop.
We’d like to thank all of you who have sent NWAC your observations. If you are out in the mountains, let us know what you see.
Weather Synopsis
A strong warm front lifting over the area this morning is directing heavier precipitation into the Olympics and north Cascades. Precipitation will fill in for areas further south later this morning and the trailing cold front should swing through the Washington Cascades around 1 PM. This storm system will bring heavier precipitation amounts to the volcanoes and Crystal Mt, and less precipitation for the Cascade Passes. Easterly flow will suppress snow levels in the Passes early this morning, but warmer air should push snow levels above Pass level for Snoqualmie and White Passes by late morning.
With the frontal passage strong winds aloft may mix down, creating very windy conditions in the afternoon. Snow level will lower rapidly late afternoon and overnight as colder air is advected into the region. Light to moderate snow should accumulate along the west slopes of the Cascades and Mt. Hood overnight. Westerly post-frontal winds should be blusterly overnight and ease off during the day on Friday.
Shortwave ridging will build over the area on Friday representing a relative break in the action, but there will still be a chance of showers for the mountains with lingering instability and weak onshore flow.
With the frontal passage strong winds aloft may mix down, creating very windy conditions in the afternoon. Snow level will lower rapidly late afternoon and overnight as colder air is advected into the region. Light to moderate snow should accumulate along the west slopes of the Cascades and Mt. Hood overnight. Westerly post-frontal winds should be blusterly overnight and ease off during the day on Friday.
Shortwave ridging will build over the area on Friday representing a relative break in the action, but there will still be a chance of showers for the mountains with lingering instability and weak onshore flow.