Hatcher Pass

8″ of new snow with 0.8″SWE @Frostbite at 2700′ and 10″ of new snow with 1″ SWE@IM at 3550′ were reported in the most recent April 4th storm. These totals finally surpassed the 5′ mark for snowpack height on the Marmot lodge snowstake! Due to the mostly right-side-up snowfall combined with light winds, we observed few recent avalanches in the field on Friday. One large persistent slab was observed up the Valley of Sin on the Ripper’s Delight on a NW aspect at 4200′ that occurred on 4/4. This avalanche likely failed on weak sugary snow sitting on a firm and smooth bed surface (as seen in photo below). Several small dry loose sluffs were observed on Friday. One human triggered persistent slab was triggered on the NW aspect of lower Microdot at 4000′. This avalanche sympathetically triggered two other slab avalanches (see photo under problem 1). 

4/4 Natural avalanche on Ripper’s Delight up the Valley of Sin NW 4200′

4/5 Recent small dry loose avalanches on The Knob above Goldmint parking lot. A few appear to be dry loose that transition at the bottom into wet loose. W 2400′

Persistent slabs 8-30″ thick will be possible to human trigger on all aspects, at all elevation, on slopes 30º and steeper.  Over 30″ of new snow has been recorded from the last two storms on 3/30-31 and 4/4.  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.

Three remotely triggered avalanches occurred on 4/1 and 4/2 followed by another storm that deposited 10″ on 4/4.  On 4/5 a large human triggered slab avalanche occurred on lower Microdot that sympathetically triggered two other avalanches (photo below). Obs here. The slab thickness will vary depending on aspect and elevation. Expect thicker slabs up to 30″ at upper elevation or on leeward (northerly) aspects and thinner slabs 4-8″ thick at low elevation or on windward (southerly) aspects.

4/5 Human triggered persistent slab that sympathetically triggered two other slab avalanches. No one was caught and carried. Lower Microdot, WNW 4000′ SS-ASy-D2-O

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 amble 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.

Dry loose avalanches (sluffs ) will be possible to human trigger on the northern half of the compass, west through east aspects (clockwise) at all elevations on steep convexities and rollovers in terrain 40º and steeper.  They are most hazardous if you are caught and carried into a terrain trap such as a gully, cliff, or couloir.  While most sluffs will be small, getting caught in steep terrain that funnels into any terrain trap has the potential to increase the size, risk and consequence of an avalanche.

Cooler overnight temperatures will keep snow surfaces dry and loose through most of the day on true north.  On aspects where dry unconsolidated snow sits on firm bed surfaces, sluffs will be more likely to trigger and result in a larger volume of debris. It will be possible to get caught and carried, injured, or tweek a knee in this terrain. Sluff management and mitigating a sluff may be challenging today due to the slow nature of the snow and inability to get enough speed to ski or ride fast enough to avoid or outrun debris.

WET AVALANCHES

With the combination of green-housing and/or sunshine in the forecast expect wet loose avalanches to be possible to human trigger in the afternoon on terrain 40º and steeper on the southern half of the compass, southeast through southwest aspects (clockwise). Slight shifts in aspect will determine whether a sluff is dry or wet and might start dry and end wet.  Timing your assents and descents will make all the difference for quality of skiing or riding today.