Today strong outflow winds will be transporting 3-4” of new snow that fell overnight. Expect Northwest winds to increase this morning to 20-30’s mph along ridges. Taller, more exposed ridgetops and channeled terrain may see gusts in the 40’s or 50’s. Blowing snow will be your first clue wind slabs are forming. Wind slabs could be a few inches thick or up to 1-2’ if they break into a older snow buried this past weekend. Two days ago we observed a similar situation where a period of strong NW winds initiated a handful of natural wind slabs and several people triggered wind slabs in steep terrain.
Keep in mind a Northwest wind direction creates unusual wind loading patterns opposite our normal Easterly storm track direction. Sunburst weather station doesn’t often reflect the full extend of NW winds and sometimes a South or SW wind direction is observed. Smooth, pillowed surfaces on steep leeward terrain will be most suspect. Wind slabs could be small and isolated or large enough to bury a person if one releases in older snow. Although its becoming less likely in Turnagain Pass, the MLK buried surface hoar is widespread and sits 1.5-3’ below the surface. More on this below.
Cornices are large and strong winds today will be adding additional stress. Give them extra space as they can break farther back onto a ridge than expected.
NW winds from two days ago (2/19) observered on Taylor Pass. A similar if not stronger wind event is expected today. Blowing snow is an obvious sign of instability. Photo by Ray Koleser
Wind slab in Placer Valley Tuesday was likely triggered by snowmachiners along the ridge during a period of active windloading. Overnight we’ve recieved a few more inches of new snow and additional loading is expected today. Photo by Graham Predeger.
Several persistent weak layers exist within the snowpack across our region, including near surface facets buried on Saturday (2/16.) This is the most likely layer to be initiated today under 1-2’ of snow. In the periphery zones of Summit Lake and Johnson Pass an overall poor snowpack structure with a variety of weak layers are lurking including the MLK (Martin Luther King day) buried surface hoar and facets mid-pack. The MLK layer has been documented throughout the entire advisory region and was responsible for a number of large human triggered avalanches in late-January and early-February. Although these deeper persistent weak layers have not been reactive lately, additional loading from recent snow and strong winds today may start to tip the balance. It is good to keep in mind that triggering an avalanche today could to step down into old weak layers and initiate a larger more dangerous slide. This is more likely in and around Summit Lake where a thin and weak snowpack is more vulnerable.
Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. New glide cracks are opening up around our region and the most recent glide crack to avalanche was a few days ago on the south side of Goat mountain in Girdwood Valley. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks.
Yesterday: Skies were overcast becoming obscured as snow started falling mid-day. 2-4″ of new snow fell (0.2 -0.4″ SWE) overnight. Easterly winds increased later afternoon to 10-15mph with gusts in the mid-20s mph. Temperatures were in the teens (F) at ridge tops and upper-20s (F) near sea level. All precipitation remained as snow.
Today: Snow will taper off this morning and skies will start to clear by this afternoon. Northwest outflow winds will increase this morning in channeled terrain and along ridgetops. Expect strong winds 25-35mph with gusts in the 40-50’s to last through the day before decreasing this evening to moderate. Temperatures will be in the teens (F) at ridge tops and low-20s (F) at lower elevations.
Tomorrow: Clear skies and sun are on tap for Southcentral this weekend and into next week as high pressure sets up over mainland, Alaska. Outflow winds will dissipate by tomorrow morning. Temperatures could dip into the single digits (F), but are expected to be more in the teens to low 20F’s. Expect inverted temperatures, cooler temperatures associated with valley bottoms and warmer temps in the Alpine. Valley fog is likely.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||24||4||.4||62|
|Summit Lake (1400′)||23||3||.2||32|
|Alyeska Mid (1700′)||23||3||.15||61|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||21||SE||9||19|