Hatcher Pass

Since receiving 10″ of snow and 1″ of snow water equivalent on April 4th, Hatcher Pass has seen some of the best skiing and riding conditions of the season with a largely rightside up snowpack, cold, dry snow and intermittent good visibility. On 4/7, we had blue skies for most of the day and recreators explored a substantial amount of skiable terrain within the pass. Several reported it as “the best day of the season.”

We also got some feedback on the March persistent weak layer which got buried by both the 3/31 Easter Storm and recent 4/4 cycle. Depending on aspect, this layer is either melt freeze crusts or old, buried wind slabs with weak, sugary snow (facets) above and below. Several noteworthy skier triggered/remote skier triggered avalanches occurred on 4/7 and failed on the same PWL.

4/7 Remotely triggered persistent slab on Stairstep WNW 4000′. SS-ASr-D2-O. While last week’s avalanches have been small, terrain traps (seen here) could act as consequence magnifiers if caught and carried.

Reported April Remote Rider/Skier Trigger Avalanches:

Colder overnight temps have loosened some of these buried crusts and we have had several days of no reported skier triggered avalanches. However, it is still possible to find this weak layer in isolated terrain features. We are also still seeing signs of instability in snowpit tests (see 4/9 and 4/10 forecaster observations).

Skiers and riders have been maximizing the winter reset.

The powder has been excellent and the pass shows it. While cold daytime (20s) and overnight temps (teens) in the mid and upper elevation have kept snow conditions light and fluffy on northerly aspects, we did see a short lived warming/wet loose cycle on southerlies on the 7th and again on the 10th. We now have new crusts on these aspects which in addition to impacting current ski quality will likely be a new layer of interest with incoming precipitation Thursday afternoon into Friday morning. Other observed and reported avalanches include small dry loose sluffs on north facing terrain.

4/10 Natural Loose Wet Avalanches on South Aspects at 4200 feet

4/10-4/11 Storm Cycle: 

With another April storm, Hatcher Pass will receive up to 20″ of snow by end of day on Friday. Expect another change in paradigm as we experience another loading event. South shifting Southeast to Southwest winds are expected to begin the storm.

Thursday Storm Totals. NWS 4/11 0400AM

Friday Storm Totals. NWS 4/11 0400AM

The 30″+ of storm snow from the Easter Storm and 4/4 (National Burrito Day) storm cycles has gently settled. Persistent slabs 8-24″ thick will be possible to human trigger on W-N-E aspects, at all elevations, on slopes 30º and steeper.

4/7 Remote skier triggered avalanche on the Women’s Run 3,600′ NW. SS-ASr-D2-O.

Hatcher Pass has seen at least 6 remote skier triggered avalanches last week, with 4/7 being the single most reported day.  With temperatures remaining below freezing, we have not had the spring warmup conditions necessary to fully “heal” this problem. Possible locations to trigger a persistent slab include any aspect where more cohesive slabs are sitting over weak sugary snow on firm crusts.  The good news is the continuity of the weak layer does not exist everywhere so finding a slab/weak layer combo will be challenging and less likely. The bad news is if you do find a location where this recipe exists, triggering a large avalanche will be possible.  Shallower spots in the snowpack or areas previously scoured down to old melt freeze crusts by the wind prior to the last two storms will be more likely locations to trigger a slab.

Remotely triggered avalanches will be possible from below, above, or adjacent to slopes.  This type of avalanche problem often gives unreliable feedback. Cracking and whumping may or may not occur prior to triggering an avalanche. Pole/probe tests and formal stability tests will help you identify stiffer snow over weaker snow and where this problem exists.

TRAVEL ADVICE: 

While skiers and riders have explored lots of the available terrain in the forecast area, tracks on a slope does not mean it is safe. 

Travel protocols will be essential today. We will be choosing to travel one at a time and spacing out through avalanche terrain, paying close attention to utilizing safe zones well out of the way of the potential runout of avalanches, avoiding crowded slopes, and be digging test pits to improve the accuracy of our slope scale assessments and go-no-go decision making. Evaluate snow and terrain carefully avoiding the largest and broadest slopes and avoiding terrain traps.

Red flags:

• Our primary red flag to look for today is upside-down snow. This indicates a flaw in the snowpack that should be completely avoided. Simple probe testing or pole testing can easily reveal stiffer snow overlying weaker snow. Areas with a right-side-up snowpack exist, and if found harvest it.
• April has returned winter to us with ample new snow.  Our human desire to recreate in these conditions is a strong lure. Curbing your desire with a heightened approach will be key to your safety.
• Recent avalanches shooting cracks and collapsing may not be present prior to triggering an avalanche.
• It may take multiple riders to trigger an avalanche and this may mislead you in your safety assessment.

The incoming storm is forecasted to come in with moderate gusting strong (40+mph) south winds. As the storm builds, winds will shift S>SE>SW. With plenty of existing low density snow available for transport, expect to see wind slabs building on NW-N-NE aspects throughout the day. These will be small (D1-D2) but possible and reactive to human trigger by the afternoon.

Observe signs of active wind loading such as pluming or blowing snow and make terrain selection choices accordingly. For surface clues, look for textured wind efffect  and tell tale red flag signs of instability like whumphing and shooting cracks.

4/11 wind directions and speeds. 4/11 0403 AM National Weather Service AVG