ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Thursday March 7th, 2019
Posted by Heather Thamm on 03/07/19 at 7:00 am.
The Bottom Line
Low Avalanche Danger
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

LOW avalanche danger is expected today, but if  more snow falls than forecasted, the danger may rise to  MODERATE.    Pay attention to changing weather. Watch for shallow wind slabs forming in the afternoon with 1-2″ of new snow and increasing winds. Avoid travel under glide cracks and give cornices a wide berth.

Good travel habits, such as exposing one person at a time, watching your partners and re-grouping in safe zones are key ways to minimize risk.

1. Low
Alpine
/ Above 2,500'
Avalanche risk
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1. Low
Treeline
/ 1,000'-2,500'
Avalanche risk
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1. Low
Below Treeline
/ Below 1,000'
Avalanche risk
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Special Announcements

  • Don’t miss an evening with renowned snow scientist Ed Adams tonight, March 7th!! The American Society of Mechanical Engineers is hosting an evening lecture delving into snow micro-structure and how it relates to the white stuff we love to play on. More details HERE.
  • Heading to Hatcher Pass? Be sure to check out the Hatcher Pass Avalanche Center mid-week snow and avalanche summary HERE.  
Avalanche Problem 1
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
  • TYPE
    Wind Slabs
  • Size
    Historic
    Very Large
    Large
    Small

Following a two-week stretch of sunny skies and spring-like conditions we await a weather pattern shift. Several storms are on tap tomorrow and into the weekend. Winds will be the first thing to change today. Expect light Easterly winds to build to Moderate (10-25mph) by the late afternoon and 1-2” of new snow possible. Shallow wind slabs may form on leeward features, but we don’t expect the avalanche danger to rise until tomorrow with more snow. However, pay attention to changing conditions and if more snow falls anticipate thicker wind slabs.

The storm tomorrow could produce up to a foot of snow and more is on the way Saturday into Sunday. In anticipation of this weather shift, we have been closely mapping surface conditions. Surface hoar has been observed from valley bottoms to the Alpine and is resting on a variety of a sun crusts on Southerly facing slopes. On shaded aspects surface hoar and 4-8” or so of soft near surface facets sit over a firmer base. Along ridgelines and areas affected by the NW wind a few weeks ago, there is hard sastrugi, wind crusts and/or rime crust. This set-up does not bode well for future bonding and will be our next concerning layers once buried.

Things to keep in mind if you are headed into the backcountry today:

  • Wind slabs – Look for drifting snow on leeward features this afternoon and pay attention to slab thickness. Older loose snow is available for transport, in addition to a few inches of new snow today. Adjust your plans if you see shooting cracks and slabs thicker than 6” — evidence the avalanche danger is increasing.
  • Glide avalanches – These types of avalanches are highly unpredictable and not associated with human triggers. It’s always best to watch for and limit exposure under glide cracks.
  • Dry-loose sluffs – Watch your sluff on steep Northerly slopes where a sun crust doesn’t exist.
  • Cornice fall – As always, give cornices a wide berth.
  • An outlier slab avalanche – Although it is unlikely a person could trigger a slab avalanche, the mountains can harbor surprises, especially in thin snowpack areas. South of Turnagain in the Summit Lake and Silvertip zones there is a shallow snowpack with a generally poor structure. A variety of old weak layers (facets and buried surface hoar) sit in the mid and base of the snowpack. The most suspect place to trigger an avalanche is steep terrain with old, hard wind slabs sitting on weak snow. Increased winds may add more stress to these old layers in Summit Lake area and Johnson Pass.

Surface hoar sits on a variety of surfaces: loose snow, firm sun crusts, and hard wind board. Our current surface conditions will become our next layer of concern with more snow tomorrow through the weekend.  

Mountain Weather

Yesterday: Skies were partly cloudy. Temperatures were in the 20s F to low 30s. At lower elevations temps bumped into the mid-30s F during the day. Ridge tops winds were light from the West shifting to the East overnight. No precipitation fell.

Today: Expect overcast skies and winds to increase this afternoon. Ridge tops winds from the East will start out light 5-15mph and increase into the 20s mph by the afternoon. 1-2″ (0.12″ SWE) of new snow is possible today and 2-6″ new snow overnight. Temperatures in the upper elevations will be in the 20s F. Sea level temps will increase into the 30s F and rain/snow line may reach 500′.

Tomorrow: Snow showers are expected to increase tomorrow morning and into the afternoon with 4-8″ of new snow possible. Easterly ridge top wind will be in the 30s mph with gusts in the 40s mph. Temperatures will be in the 20s F in the upper elevations and 30s F near sea level. Expect snow to transition to rain at lower elevations.. A more powerful storm is expected Saturday into Sunday with another shot of snow accumulation, stronger winds and warmer temps.

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  30 0   0   57  
Summit Lake (1400′) 28   0   0   27  
Alyeska Mid (1700′) 31    0 0   52  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22   W –> E 5   14  
Seattle Ridge (2400′) 27   SW –> SE   3   9