After two weeks of high pressure the jet stream has shifted and the first of two big storms is here. Overnight 1-3“ of snow fell, favoring Girdwood so far, and an additional 6-10” is expect today across the region. Strong Easterly ridgetop winds 30-40mph will continue all day. Sunburst has already seen gusts in the 50s mph. Temperatures have also risen and rain/snow line should reach 1000’ by mid-day. As snow and winds continue storm slabs and wind slabs will be growing in size. Monitor slab depths and avoid slope angles greater than 35 degrees. Leeward aspects could have deeper more connected slabs due to strong winds transporting snow. Also don’t forget about the weak surface conditions this new snow is falling on. Surface hoar and near surface facets are sitting on hard surfaces (sun crusts and wind-packed snow.) Basically this set-up does not bode well for future bonding. As we get more snow and wind this weekend and slabs grow thicker the avalanche hazard will continue to increase.
Wet Snow – Below 1000’ where rain is falling on dry snow on Northern aspects, triggering a loose-wet avalanche will be possible. In Portage Valley where precipitation amounts will be greater, natural avalanches are possible in steep channeled terrain and may entrain wet snow into the lower elevations. Avoid traveling on trails or terrain directly under steep avalanche paths.
South of Turnagain in the Summit Lake and Silvertip zones: Similar surface conditions to Turnagain Pass exist and any new snow that falls today is not expected to bond well. In addition a variety of old weak layers (facets and buried surface hoar) sit in the mid and base of the snowpack and wind loading and new snow will be adding more stress to these layers. Although less snow is expected to fall in this zone today keep in mind uncertainty exists for triggering a deeper more dangerous avalanche.
Surface hoar was present on all elevations and aspects prior to todays storm and was capped by a trace of new snow a few days ago.
Surface hoar sits on a sun crust on Southerly aspects (photo on left) and near surface facets exist on shaded aspects (photo on right.) In addition facets have been found under sun crusts and under thin wind slabs. We have plenty of weak surface snow issues to be concerned about.
These types of avalanches are highly unpredictable and not associated with human triggers. A number of cracks are located in popular terrain like Magnum’s SW face, Corn Biscuit, Lipps, and Repeat Offender on Seattle Ridge. The last glide avalanches to release naturally were a week ago on Seattle Ridge and in Girdwood Valley on Penguin, Goat, and Raggedtop. The best way to manage this problem is to watch for and limit exposure time under glide cracks.
On the left a glide avalanche released on Seattle Ridge on March 1st. On the right a glide crack continues to open on Repeat Offender. Photos courtesy of Allen Dahl.
Yesterday: Skies were overcast. Easterly ridge top winds increased from light to moderate (15-25 mph) by the afternoon. Winds increased overnight with several gusts in the 50s mph this morning. Temperatures at ridge tops were in the low to mid-20s F and temperatures at sea level were in the mid-30s. Light flurries were observed late afternoon. Precipitation increased overnight and Alyeska midway station has seen 3 €œ new snow (.39″ SWE) and 1″ of new snow was recorded at Center Ridge. Temperatures at sea level this morning are 37F and rain is falling to ~500′.
Today: Stormy weather will continue today and overnight. An additional 6-10 €œ of new snow (~0.5 € SWE) is expected above 1000′ and will fall as rain at lower elevations. Portage will see higher precip totals due to its coastal location. Winds will be strong 30-40mph from the East with gusts in the 50s mph. Temperatures will increase throughout the day with a high of 40F at sea level. Rain/snow line could reach 1000′. Overnight another 4-8″ of snow (.43″ SWE) is possible.
Tomorrow: A second storm is tracking towards the Gulf of Alaska from the South and will arrive Saturday. This storm looks to have stronger winds, warmer temperatures and higher precip totals. Another 1-2′ of snow is expected in the upper elevations and rain below 1500′. Rain, snow and strong winds are expected to taper off Sunday afternoon.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||31||1||.1||57|
|Summit Lake (1400′)||31||0||0||27|
|Alyeska Mid (1700′)||31||3||.39||53|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||26||SE||14||32|