The Bottom Line: Avalanche problems should be confined to specific terrain features Friday. Recently formed wind slabs may still be lingering on steep lee slopes above treeline. Think about the increasing potential for loose wet avalanches on steep southerly facing slopes during expected warm sunny weather Friday. Remember, we don't have any specific snowpack observations from the Hurricane Ridge area during the government shutdown, so you will need to account for the extra uncertainty before entering avalanche terrain.
Snow and Avalanche Discussion
Look for lingering wind slabs above the most recent rain-line on steep unsupported slopes at higher elevations. Approach steep unsupported slopes with wind-drifted snow cautiously, feeling for firm or hollow sounding snow as a sign that wind slabs may be present. Be aware that potential afternoon sunshine will increase the odds for loose wet avalanches. These avalanches are most likely to release from steep, rocky, sunny slopes as the day progresses. Monitor changes in the upper snowpack, looking for natural pinwheels or small loose wet avalanches as clear signs of increasing danger. Avoid terrain traps like gullies where even a small avalanche can bury you.
We received another recent observation from the Olympic mountains. Low snow coverage below 4000' and evidence of many strong crusts throughout the snowpack told the story of multiple rain events in this area, as well as recent avalanches on lee slopes at higher elevations.
Right now we are forecasting without specific snowpack and avalanche observations from the Hurricane Ridge area due to the government shutdown. If you travel to the Olympic Mountains, please help your local forecast by submitting an observation.
Fri 25th Jan 16:19 - Robert Hahn
Weather Synopsis for Friday night through Sunday
The high-amplitude upper-level ridge offshore pushes slightly further into the region with temperatures aloft warming further tonight into tomorrow, giving us the warmest temperatures we've experienced since November over our mountains by late Saturday into Sunday. Weak systems are spilling over the top of the ridge into SE Alaska and are dropping south through the Rocky Mountains, leaving our region largely unimpacted. Low-level moisture is generally decreasing, so clouds should be mostly clearing out on Saturday. Low-level inversions and fog or freezing fog are likely in some locations. Saturday will be the warmest day for our mountains since November 19th, with freezing levels pushing 11000 ft. On Sunday, a trough moving east along the Rockies will knock back temperatures slightly in our region, but it will remain unseasonably mild.
Sun 20th Jan 09:00
January 20, 2019
The recent weather pattern of lower accumulation storms (by NW standards) and longer stretches of calm weather should continue as we move into late January. Since January 17th, incremental snow accumulations punctuated with rising freezing levels favored the south and eastern parts of the region. Storm instabilities have risen with storms and gradually subsided.
New Snow Problems
New Snow Problems
Storms over the past week have brought a range of layers from rain crusts, to heavy moist snow, to stiff drifts, to light dry powder. Some storm days, like the 18-19th, saw reactive, but very short-lived avalanches caused by heavy precipitation and wind. Even the longer-lasting avalanche problems, wind slabs, haven't persisted for more than a few days. Where the recent snow is stressing underlying weak layers, more dangerous avalanche conditions have prevailed.
Old Snow Problems
Old Snow Problems
Persistent weak layers (PWLs) have been a constant in the eastern zones of the Cascades this winter. As usual, they have been much less problematic at the Passes and west of the Cascade Crest. The latest PWL is a layer of surface hoar, buried around January 17th and found generally east of the Cascade Crest. Buried surface hoar is an active weak layer in the eastern zones and can be found to a limited extent on the eastern edge of the Stevens and Snoqualmie Pass zones. There few, if any, avalanches have been reported on the buried surface hoar. It may be most problematic in open, wind-sheltered terrain, especially well above the valley floor.
You are most likely to find other layers of old weak snow the further you move east from the Cascade crest. Here snowpacks are shallower, more variable, and generally weaker. In some locations, weak snow near the ground can still be found. These basal facets have hung around all season. Digging profiles and using snowpack tests is the best way to gain information about these old persistent weak layers. However, snowpack tests are just one piece of the puzzle. Your terrain decisions shouldn't hinge on any given test result. Because of the size of our forecast zones and the variability in the snowpack, it's important to make snow observations as you travel. We’ll keep watching these old layers, but let us know what you see while you are in the mountains.