Special Avalanche Conditions
Generally increased avalanche danger mid-late Wednesday into the Memorial Day weekend…
Past: Recent cooler and wetter than normal spring weather conditions have mostly allowed for slow snowpack settlement and consolidation. However, increased daytime warming in late May combined with intermittent sun breaks have produced isolated cornice collapses and some natural slide activity that has included both significant wet loose and wet slab slide releases (such as reported in various posts on TAY and from WSDOT avalanche crews at both Chinook and Washington Passes). As a result, while it is almost June (which is often considered summer in some states) any steeper terrain that has not experienced at least some natural slide activity should be approached with extreme caution from an avalanche standpoint, especially during periods of sunshine or warm temperatures when the potential for further slide releases should be greatest.
Current: A moderate frontal system should spread increasing rain or snow northward over the region Wednesday into early Thursday, along with lowering freezing levels and increasing ridgetop winds. Forecast models indicate
* up to an inch or more of water equivalent during the next 24-30 hours ending mid-day Thursday
* heaviest amounts along the Cascade east slopes and near the volcanoes,
* most of the precipitation occurring as rain below 4000 feet, a mix of rain and snow from 4 to 5000 feet, and mostly snow above 5 to 6000 feet
* increasing and shifting winds at higher elevations which should mostly load west to northwest exposures Wednesday and north thru east exposures Wednesday night into Thursday morning
Future: After briefly decreasing and more showery precipitation mid-day Thursday, a second though weaker front should send renewed light rain or snow northward over the area later Thursday into early Friday at continued relatively low freezing levels and further moderate ridgetop winds. This should deposit smaller but not insignificant amounts of snow to most mountain locations above 4 to 5000 feet, with intermittent snow down to around 3500 to 4000 ft. As a result, up to a foot or more of new snow is possible from Wednesday into early Friday above 5 to 6000 feet with lesser amounts down to around 4000 feet and up to a few inches around the 3500 ft level. While relatively cool conditions should persist Friday into Saturday morning with only limited partial clearing, any sun breaks that do occur should rapidly warm, melt and weaken surface snow and produce an increasing likelihood for both natural and human triggered avalanche releases.
Slow warming and more sun breaks likely Saturday afternoon and Sunday should allow for dangerous avalanche conditions thru further warming, melt and weakening of recent snow or newly formed cornices, and travel in steeper sun exposed terrain is not recommended during the heat of the day. Careful snowpack evaluation, cautious routefinding, and conservative decision making should be essential to help ensure safe travel. Note that many avalanche paths have filled in recently from previous avalanching. As a result, new avalanches involving the most recent snow may travel long distances and extend into terrain below the snow line.
Climbers or other recreationalists venturing into higher terrain on the volcanoes (>7000 ft) should be aware that winterlike snowpack and weather conditions likely during the rest of the week should slowly moderate over the weekend. However, this moderation will likely result in greater danger due to rising freezing levels and greater sunshine effects…especially mid-late Saturday and Sunday…when recently deposited wind slabs or cornices should be more likely to release.
This is not the time to be complacent about the snowpack. It is the time to make objective decisions and to focus on the snowpack and weather, neither of which should be particularly pleasant or safe for the remainder of the week ahead.