Despite the warm and sunny spring weather this week, with highs for the last two days of +10°C at the Juneau airport, the snowpack has just begun the transition to spring conditions. The greatest changes came on the 6th, the first warm sunny day, which was preceded by a warm night.

Slab avalanche activity was reported on the south side of the Mt Juneau - Mt Olds ridge in the afternoon, and a possibly fresh 30 - 50 cm deep by 300 m wide slab was observed on the north face of Mt Juneau. Sunballs, cinnamon rolls, and small wet sluffs were widespread.

The 7th was preceded by a colder night, and the snow surface at mid elevations stayed mostly frozen except on the sunniest aspects. High on Mt Stewart, we found that the surface snow on the shadier aspects remained dry and cold, mostly shallow powder with high variability due to wind, thaw, and rime crusts.

On sunny aspects and at lower elevations, the top 10 cm has turned to melt freeze snow that thaws to slush in the afternoon sun. The skiing was good, but we triggered fast moving wet sluffs on steep sunny slopes alongside the natural ones from the heat of the previous day.

The March 31 graupel layer remains weak, and may be stressed as the surface layers thaw and creep downhill at an accelerated rate. Though test values now are fairly strong on that layer, increased creep could increase the stress to the critical level for slab release.

Other than that, the wet sluffs deserve caution. Fast wet sluffs are powerful and can become quite large. As the snowpack wets out and adjusts to the warmer spring weather, it is likely to go through a period of instability, with sluffs likely and slabs possible.

The slower the thaw, the smaller the slides will be, and the harder they will be to trigger. Activity will be most pronounced with rapid warming.

The natural world often fails to conform to our classification schemes, and it is well to remember that the truth is the snow out there on the mountainside, not the artificial constructs we form about it in our heads or read in our textbooks.

The AK Block sizing table is in our Research section, along with a preliminary research paper on its development as of last fall. The final version for general use will be much simpler. It will probably be sized in round 10 cm increments and 20 Kg weight classes. We are maintaining higher precision for the research stage, until we establish just how how big the size tolerance is.

The purpose of the CAK Block is to determine the effect of the cut back on test values for otherwise identical blocks. The Rutschblock serves as a standard test to compare with the still-nonstandard AK Block tests we are developing.

Whenever we have light, midweight, and heavy testers available at a site, the current phase of research will also compare AK Block results for each tester to see if our sizing table is correcting properly for weight.

In this test block set on a 39° slope, the March 31 graupel layer at 67 cm (25 cm deep) fractured at Quality 2 (average shear) on multiple hard jumps on the Rutschblock (RB6 Q2) and Cutback AK Blocks (CAK6 Q2), and more easily on the second, harder jump on the AK Block (AK5 Q2). As is usual in our tests, none of the cutback blocks broke at the cut. The fracture of the non-cutback AK comparison block was actually easier than that for the cutback CAK block.

The second fracture at 43 cm (49 cm deep) on the March 27 - 28 snow required additional jumps on the Rutschblock and Cutback AK Block tests, but came out as a secondary fracture on the second, harder jump on the AK Block test. All fractures were irregular, so they scored RB6 Q3, CAK6 Q3, and AK5 Q3.