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Avalanche Forecast

Archived

Jan 13th, 2019–Jan 14th, 2019

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Snoqualmie Pass.

The bottom line: The avalanche danger will rise as the day warms up. The surface crust will begin to break down and weaken in the sun. If you see rollerballs or find wet snow on the surface, it’s time to start avoiding similar slopes. Loose wet avalanche debris is heavy, and can pack a punch. Don't these slides ruin your day. 

Regional Synopsis

January 10, 2019

We’re about a month into our avalanche forecasting season, and what a wild month it has been. We’ve seen the snowpack grow from near non-existent to over a 100 inches deep at Mt Baker. We’ve seen avalanche warnings blanket our coverage area, had several widespread large natural avalanche cycles, and seen persistent weak layers plague nearly every zone. While the active weather pattern has been a welcomed sight, it’s hard to catch your breath.

It looks like this weekend, and extending into next week, we are entering a calm period in the weather. High pressure over Idaho and Montana will keep Pacific storms at bay for at least the short term. As we enter this period of nice weather, there are a few things on our mind here at the avalanche center.

Old Persistent Weak Layers

A high elevation rain event on January 3rd did us a favor in many locations. Besides heavily stressing old weaklayers, the rain created a very strong met-freeze crust, making it extremely difficult to trigger deep avalanches.

There are a few exceptions, and they can be found mainly in the eastern forecast zones. The East-North zone around the Methow Valley and WA Pass did not experience significant rain above 5500 ft, potentially leaving some older weak layers in tact. Areas further east including, but not limited to, Icicle Creek and the Wenatchee Mountains did not receive enough rain to form a strong thick crust. In all of these area, older persistent weak layers are still suspect.

Higher Elevations and Remote Trailheads
Stormy weather over the last month has been keeping most of us closer to common trailheads and recreating at near and below treeline. With nice weather on tap, some of you may be thinking about heading into higher elevation terrain and exploring around more remote trailheads. If you are heading out, take time to consider a few key pieces of information.

  • At higher elevations the snowpack is very deep and wintery. This stands in stark contrast to the lack of snow at lower elevations. The snowpack you’ve seen on previous outings this winter, doesn’t represent what you will encounter at higher elevations.

  • We have not received much information about the above treeline nor remote location snowpacks. That means we have a high degree of uncertainty in these areas.

  • You will need to make observations as you travel to confirm if the avalanche forecast is applicable the the area where you are traveling. When observations lineup with the information in a forecast, its valid. If you see observations that don’t lineup, it’s time to take a step-back.

  • If you are heading into our regions highest alpine terrain, remember, NWAC forecast apply to areas below the main Cascade crest, or about 8000 ft. So, if you plan to travel to higher elevations on Mt Baker, Mt Shuksan, Mt Rainier, Mt Hood, or similar areas, you will need the skills and information to evaluate the terrain and snowpack.

If you’re heading into higher elevation terrain, remember we don’t have much information about these snowpacks, and therefore have a higher degree of uncertainty. Photo: SimonTrautman

We’d like to thank our NWAC Community for all the wonderful public observation this year. If you are heading out into the mountains, we appreciate you taking the time to let us know what you saw. This is a great way to contribute to the creation of your avalanche forecast. You can submit observations here.

Enjoy the sunshine!

Weather Forecast

Weather Synopsis for Monday night through Wednesday

Strong upper-level high pressure is centered over the Intermountain West, extending across the Pacific Northwest. This pattern is blocking Pacific storms and providing fair weather along with unseasonably high freezing levels. 

A low-pressure system is centered near the central California coast on Monday afternoon.

Freezing levels remain near 10,000 ft Monday afternoon with several NWAC stations reaching the 50's in areas away from the cooling effects of the easterly winds.

Low-level offshore flow is maintaining strong temperatures inversions with sub-freezing temperatures in the passes and lower elevations east of the crest.

The upper ridge will maintain dry conditions through Tuesday before some moisture begins to lift northward across the area late Tuesday.

Freezing levels will lower Tuesday and high clouds begin spreading northward Tuesday afternoon as the ridge begins weakening.

The low-pressure system currently off the California coast weakens and lifts northward Tuesday night and Wednesday, spreading light precipitation over the area at lowering freezing levels. The initial precipitation should remain light and generally favor the volcanoes.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.