Avalanche Forecast
Issued: Jan 14th, 2019 6:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet and Persistent Slabs.
Josh Hirshberg,
The Bottom Line: Expect one more day of warm temperatures. Use caution on steep, sunny slopes if you see rollerballs or find wet snow on the surface. Loose wet avalanches can be dangerous if they push you into trees, rocks, or off of cliffs. There is still an isolated chance of triggering a deeper slab on older weak layers.
Summary
Snow and Avalanche Discussion
There is a lot of variability of snowpack structure within the zone. The current snow surface is a mixed bag. On sunny aspects, it is likely crusted over, softening as the day warms. 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 avalanches in wind loaded terrain. 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
Tue 15th Jan 15:00 - Kenny Kramer
Weather Synopsis for Tuesday night through Thursday
Tuesday has quickly transitioned from blue bird high pressure to a mostly cloudy afternoon as high pressure departs to the east and the region begins seeing the effects of the west coast trough. Moisture has spread northward through the day from a trough that extends to southern California. Most of the energy associated with the trough has been spent in California and the PNW will only see occasional light showers in bands rotating northward through Wednesday afternoon.
Freezing levels have lowered substantially by Tuesday with many NWAC sites 10-20 degrees cooler than yesterday at the same time!
Strong easterly winds persist across the Cascades and through the passes keeping sub-freezing air in the lower elevations.
Some light precipitation will spread northward Wednesday but amounts will be very light as the main energy moves inland well south of the area.
A stronger low-pressure system will approach the offshore waters late Wednesday and move NE offshore Thursday. More significant precipitation should rotate across the area Wednesday night with wi little break between bands during the day Thursday.
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
The concern for wet loose avalanches is being maintained by warm temperatures Monday night and sun in the first half of Tuesday. Otherwise, these avalanches have mostly run their course. You could still encounter them on steep slopes that face the sun. On Tuesday, southeasterly aspects may be the most avalanche prone. A project a cooling trend and building clouds should limit avalanches by the afternoon.
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, use caution on steep slopes and near terrain traps. You can find these avalanches around gullies, cliffs, and rocky slopes. These features can increase the consequences of an avalanche.
Aspects: South East, South, South West.
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. Recent wind loading at upper elevations, warm temperatures, strong sun, and potential melt-water in the snowpack all raise uncertainty about the likelihood of triggering a persistent slab. An avalanches in 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 extreme 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 15th, 2019 5:00PM
