Avalanche Forecast
Issued: Jan 13th, 2019 6:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet, Wind Slabs and Persistent Slabs.
Matt Primomo,
The Bottom Line: The avalanche danger will rise as the day warms up. Get off of steep, sunny slopes if you see rollerballs or find wet snow on the surface. Loose wet avalanche debris is heavy, and can pack a punch. Don't these slides ruin your day. There still remains an isolated chance of triggering a deeper slab on older weak layers.
Summary
Snow and Avalanche Discussion
Folks should realize that there is a fair amount of uncertainty with our snowpack and how the warming will influence it, particularly above 6,000ft. There is also a lot of variability within the zone. The current snow surface is a mixed bag. On sunny aspects, it is likely crusted over early in the morning, and becoming wet and heavy by mid day. The snow has been remaining cold and dry above 5,000ft on shaded aspects, and small surface hoar growth has been observed. The storm snow from January 8th and 9th sits over a crust from January 3rd. A thin layer of weaker snow has been found just above this crust, and is worth checking out how these are bonding. A round of control at Mission Ridge on the 10th pulled out a number of large wind slabs. One of these on a Northwest aspect at 6300ft broke through the crust and ran on weaker snow near the ground, exposing rocks. On steep southerly aspects, a number of loose wet avalanches have been observed.
Weather Forecast
Mon 14th Jan 13:36 - Kenny Kramer
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.
Regional Synopsis
Thu 10th Jan 09:00
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.
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!
Problems
Loose Wet
With balmy temperatures on the mountain tops, and sun in the forecast, loose wet avalanche danger will increase as the day progresses. Steep slopes that face the sun are the most likely places these will happen. If you see roller balls, notice the surface crust is melting and becoming wet and heavy, or see small loose slides that begin entraining snow on any aspect, get off of steep slopes. These will be more of a concern above the cold air that is pooled at lower elevations.
Aspects: South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Be mindful of thin windslabs at the uppermost elevations where the wind may have drifted cold, dry snow into small wind slabs here and there. There are still some bigger slabs that were built during the east wind event on the 8th and 9th, but these are becoming more difficult to initiate. If you were to find one of these, it would likely be in more radical terrain. Be especially careful of steep, unsupported, and rocky slopes. Use visual clues, like snow surface texture to help you find where these areas may be. Wind slabs will often feel more firm than in non wind affected areas, and they may feel hollow underfoot. Ease into avalanche terrain by using smaller, inconsequential slopes first. Only expose one person at a time to any one particular slope.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Deeper avalanches in old snow have become less and less likely. However, the consequences are still high. Obvious clues to danger like shooting cracks and whumphs probably won’t be observed, although a weak snowpack structure still exists in some locations. These weak layers are slowly adjusting, but rapidly rising freezing levels and the sun are something to consider in that it may influence the reactivity of the slabs. In any case, slides on these deeper weak layers would be very large and surprising. You can minimize your risk by using lower angle, and well supported slopes, and staying out of radical terrain. Shallow, shaded, and rocky slopes are also good places to avoid.
Two primary layers of concern in the snowpack are:
A layer of buried surface hoar found 1-3 ft below the snow surface. This is mainly a concern above 6000ft. Be suspicious of this layer the higher you go. Documented avalanches have been on North through Southeast aspects. Snowpack tests continue to reveal sudden results in some areas on this layer.
A layer of weak, sugary facets can be found near the ground in the Wenatchee Mountains, and other areas on the eastern edge of the forecast zone. If an avalanche failed on this layer, it could be more than 4 feet deep. Use caution if you are traveling in areas where the snowpack is thinner, and where any stiff snow overlies weak snow.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 14th, 2019 5:00PM
