Avalanche Forecast
Issued: Jan 12th, 2019 6:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Persistent Slabs and Loose Wet.
Matt Primomo,
The Bottom Line: We are in a low probability, but high consequence scenario for avalanches that could break into old snow layers. Upper elevations are the main concern for these, and for shallow, wind slabs that may build from light winds. Loose avalanches will become possible with strong sun and warming temperatures during the middle of the day.
Summary
Snow and Avalanche Discussion
Folks looking to get into the high mountains should realize that there is a fair amount of uncertainty with our snowpack above 6,000ft, with the warming, and there is a lot of variability within the zone. A common structure to be found out there will be storm snow (with or without a wind slab) over a crust from January 3rd. The storm snow from January 8/9 may not be bonding very well to the crust at upper elevations, where a thin layer of weaker snow has been found just above this crust. Recent wind slab avalanches ran on the crust at Mission Ridge and were from 6" to 16" deep and from 60' to 125' wide. One started on a Northwest aspect at 6300ft and broke through the crust into weak snow near the ground. At low elevations and on southerly aspects, a number of loose wet avalanches have been observed.
Weather Forecast
Sun 13th Jan 14:16 - Dennis D'Amico
Weather Synopsis for Sunday night through Tuesday
Strong high pressure will remain anchored over the Inland NW, blocking weather systems from reaching the area through at least Tuesday.
High freezing levels and mostly clear skies will continue through Monday afternoon with a few important caveats. Constant light to moderate easterly flow will cause locally cooler temperatures in and around the Cascade Passes. Temperature inversions like the one seen this afternoon at Washington Pass stations with temperatures near 40 degrees at ridgetop (6700 ft) and a chilly 25 degrees at Pass level (5400 ft) will be common. Temperatures for areas further west of the Cascade crest like Paradise, Mt. Baker and Hurricane Ridge will continue in the 40s to even 50s through Monday. Areas of low clouds should be confined to the lower slopes on the east side of the Cascades.
The ridge will begin to shift east and be undercut by an open trough entering central California Monday night and Tuesday. This should allow for freezing levels to first begin lowering in the south Washington Cascades and Mt. Hood area late Monday afternoon. High clouds will spread northward Monday night, with a mix of high and mid clouds and steadily decreasing freezing levels for all areas on Tuesday.
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
Wind Slabs
It has been a number days since the big east wind event, but at the higher elevations the wind has been drifting the low density snow surface into thin wind slabs here and there. The recent east winds formed slabs in some unusual locations like well below ridgelines, on the sides of gullies, and in places that are often scoured. Other locations have no wind slabs at all. Use visual clues of the snow surface texture to help you find where these areas may be. Wind slabs often feel firm, and hollow underfoot. Approach steep slopes with caution, and be especially careful of steep, unsupported, and rocky slopes. Ease into avalanche terrain by using smaller, less consequential slopes first. You can stay safe by traveling on ridges, and low angle and well supported slopes.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
We are in a low probability, but still high consequence timeframe for deeper avalanches in old snow. Obvious clues to danger like shooting cracks, or whumphs may not be observed. This is why persistent slabs are difficult to assess and predict. We still have a weak snowpack structure in some locations and there is plenty of snow over these layers to act as a slab. The snowpack is slowly adjusting to the new load, but rapidly rising freezing levels and the sun are something to consider in that it may influence the reactivity of these slabs. In any case, slides on these deeper weak layers could be very large and life threatening. You can choose to minimize your risk by using low angle, and well supported slopes, and staying out of radical terrain.
There are two primary layers of concern in the snowpack:
A layer of buried surface hoar may be 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, particularly in the eastern edge of the forecast zone such as Mission Ridge and Blewett Pass. 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.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
With sky rocketing freezing levels for the upper elevations, and sun in the forecast, loose wet avalanches may become common. Steep slopes that face the sun are the most likely places these will happen. If you see roller balls, notice the snow surface is becoming wet and sticky, or see small loose slides that begin entraining snow on any aspect, get off of steep slopes.
Aspects: South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 13th, 2019 5:00PM
