The Bottom Line: There is still a chance of triggering a large avalanche on older weak layers. Use caution on slopes over 35 degrees and where avalanches can start. Stop and regroup out of avalanche terrain.
Summary
Weather Forecast
Wed 16th Jan 14:52
- Robert Hahn
Weather Synopsis for Wednesday night through Friday
A strong closed low slowly weakening and filling off the California coast is beginning to veer northward while it sends a chunk of energy directly into California. Wednesday night, a weakening band of moisture will lift northward and spread moderate snowfall to Mt. Hood and the east slopes of the southern WA Cascades with lighter snowfall for other areas.
On Thursday, expect increasing S then SW flow as the low tracks about 250 miles off our coastline, with continued cool easterly flow through the passes. Periods of light snow are expected with higher snow levels west of the Cascade crest. The main energy with the low will arrive from the SW late Thursday, bringing moderate rain and snow throughout the region into Thursday night. A wind shift late Thursday night is likely to change Snoqualmie pass to rain, but slightly higher elevations will remain snow.
On Friday, rain and snow showers will decrease as the initial low departs, but a second low tracking to our NW, well offshore, will spread increasing moisture to our coastal regions late in the day as snow levels rise.
Regional Synopsis
Tue 15th Jan 09:00
January 15, 2019
We’re about a month into our avalanche season and well into the heart of winter. In the past month, the snowpack has grown from near non-existent to over a 100 inches deep at Mt Baker. Remote weather stations show most snow depths across the region are at 62-77% of normal with Mt Baker and Crystal Mountain at 93% and 90% respectively. Check out the latest climatological snow depths for more details.
Much of the last month has been filled with elevated avalanche danger, numerous avalanche warnings, and several widespread large natural avalanche cycles. While the active weather patterns and growing snowpack have been a welcomed sight, it’s been hard to catch our breath. Quieter weather in the middle of January has offered a break in the non-stop storms and allowed avalanche danger to drop in all zones. Looking forward to more unsettled weather, there are a few things on our mind here at the avalanche center.
Calm weather in mid-January
A period of calm weather heading into the middle of the month shaped a variety of snow surfaces. As of January 15th, you could find a range of wind transported snow, crusts (both thin/breakable and thick/supportive), rime, surface hoar, and weak, dry snow on the snow surface. This will determine our next interface to track, as storm snow accumulates. The big take-away is that you should track surface conditions from the 16/17th and how that interface changes based on aspect and elevation.
There were a few interesting weather factors during the mid-January calm weather that contributed to surface variations. While clear skies and warm temperatures were the norm in many locations (especially west of the Cascade Crest), temperature inversions and cold east flow cooled valleys and passes. The sun is still low in the sky and hasn't been strong enough to drive significant melting of snow surfaces. Hence, many slopes developed only thin crusts. Additionally, fog limited both the effects of the sun and surface hoar growth at lower elevations and in valleys.
Old Persistent Weak Layers
A high elevation rain event on January 3rd did us a favor in many locations. Besides heavily stressing old weak layers, the rain created a very strong melt-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 intact. 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 areas, older persistent weak layers are still suspect.
An avalanche on a persistent weak layer in the East-Central zone. Photo: Matt Primomo
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 to the area where you are traveling. When observations lineup with the information in a forecast, it's 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 forecasts 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: Simon Trautman
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.
Problems
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.
