Valley temperatures have remained at or above freezing for the last 72 hours with  rain on snow expected to occur as high as 2000′ today.  An additional .5-1″ of SWE is forecasted today that will favor the maritime climate zone.  As rain is able to saturate the upper snowpack and above freezing temps push deeper into the snow the likelihood and size of wet loose avalanche activity will be on the rise.  In the intermountain zone on 4/28 the top 3 feet of the snowpack was wet with moist snow beneath up to 3000′.  Human triggered wet loose avalanches are likely in terrain steeper than 35° where the surface snow is wet and ski penetration is greater than 6 inches due to unfrozen snow.  The size of wet loose activity will directly correlate with the vertical relief of the slope involved and the depth of unfrozen snow.  

Avoid being exposed to or traveling on slopes steeper than 35° where the surface of the snow is wet or ski penetration is greater than 6 inches due to unfrozen snow.  The hazard for this problem is on the increase as heavy rain on snow is occurring with high temperatures on the increase region wide.  Wet loose activity may be able to step down to deeper layers in the snowpack creating more destructive avalanches.

Precipitation has been increasing in intensity over the last 4 days.  8-16 inches of new snow since the 25th is likely to exist above ~4000′ by the end of today.  Lower amounts exist at mid elevations due to temps at or above freezing preventing more than a few inches of moist snow from accumulating.  At low elevations rain is falling with temperatures remaining above freezing.

 Temperatures have been steadily increasing along with snowfall intensity since the 25th. This is creating upside down storm slabs (denser snow at the surface) that will be reactive to human triggers up to 2 feet in depth on terrain steeper than 32° above 4000′.  Pay attention to new snow amounts and watch for signs of instability such as shooting cracks, collapsing or recent avalanche activity.

Storm slabs will be more sensitive where they overlie a layer surface hoar that was buried on 4/22(see problem 3).  This layer is very specific, and exists at upper elevations on protected north aspects.  This layer is less likely to exist in areas that are in close proximity to wind channeled terrain.  

Moderate to heavy precipitation is expected today with snow lines rising to 2000′ and an additional .5-1″ of SWE expected.  This will translate to top heavy storm slabs up high putting pressure on the 4/22 buried surface hoar layer in specific locations, and rain down low increasing the likelihood for wet loose activity.

Triggering a persistent slab avalanche up to 2 feet in depth is likely today in specific locations at upper elevations.  Storm totals are unclear but are likely in the 8-16 inch range above 5000′ by the end of today.   This new snow will be building an upside down storm slab atop a layer of buried surface hoar that exists at high elevations on protected north aspects.  The sensitivity of this layer will likely vary greatly from one location to another.  Sensitivity will be affected by depth of new snow and the presence, or lack of buried surface hoar.   Slope by slope assesment is encouraged if traveling in steep and/or consequential terrain of mid-upper elevations.  It is recommended to avoid slopes steeper than 32° where buried surface hoar is identified with a cohesive slab above.

Surface hoar found on 4/21 prior to being buried on a north aspect at 5500′ just north of Hippie Ridge.  This is a potentially dangerous weak layer at upper elevations as incremental snowfall increases stress on a layer that is notoriously weak in shear and can persist for long periods.

The likelihood of deep slab avalanche activity occurring, is slowly increasing as the overnight freezing line climbs in elevation.  As our snowpack makes the transition from a winter pack to a spring one, deep slab avalanches become increasingly possible.  The most likely trigger to this avalanche problem would include significant wet loose activity or cornice fall.  It is highly recommended to avoid traveling on or exposing yourself to cornices, and steep solar aspects where the surface is saturated.  As the season progresses and temperatures continue to rise, so does the possibility for deep slab avalanches to occur.

Weak snow exists at the base of our snowpack.  On 4/15 our area saw the first deep slab activity occur since late February.  This occurred on Meteorite (see avalanche activity section) and was a cornice fall that triggered a series of step down avalanches that eventually stepped down to the ground.  This is a clear indication that large triggers can have an affect on depth hoar.  Increasing temperatures are expected to produce more significant activity later in the season while our snowpack is undergoing a transition from a winter snowpack to a spring one.  

This problem is very difficult to assess due its depth and the fact that signs of instability will likely not be present.  You can stack the odds in your favor by avoiding steep terrain that is undergoing rapid changes such as strong solar and avoiding exposure to large triggers such as cornices.  

Large natural avalanche on Meteorite triggered by cornice fall on 4/15.