The avalanche danger is generally LOW today. Expect firm spring snow conditions this morning with mid day softening. Watch for wet avalanche activity as the sun heats up the slopes especially around rocks and places where the snow coverage is thin. As usual, you should get out early and get home early.

 

The following is the spring snowpack conditions statement.

Avalanche Concern #1 Wet Snow Instability:

Wet snow avalanches can occur anytime during the spring and early summer. This time of year the sun is close to its maximum strength. If night time low temperatures are above freezing, the snow warms up rapidly. If skies are cloudy overnight, you can expect wet snow avalanche conditions by mid morning. If the snow gets a good refreeze, avalanche conditions can occur later in the day. You can use the Mammoth Mountain Ski Patrol site, http://patrol.mammothmountain.com/OtherWxStations.html or

http://www.wrh.noaa.gov/mesowest/mwmap.php?map=hnx

to monitor air temperatures throughout the forecast area.

Boot-top deep wet snow, significant roller ball activity, or any wet snow avalanche results from small test slopes all indicate that wet snow instabilities can occur. Moving to a different aspect with less sun exposure, terrain less than 25 degrees in slope angle without steeper terrain above it, or simply heading over to the local crag all represent great choices at this point.

Avalanche Concern #2 Deep Wet Slabs:

Deep wet slab avalanches represent the second spring avalanche concern. A deeply buried persistent weak layer still exists on some NW-N-NE aspects. In some areas melt water may percolate through the snowpack and form melt channels through the layers or the melt water may percolate through the snowpack and form melt channels through the layers or the melt water may simply weaken this layer and cause it to lose strength and fail. There is no way to know where this snow structure exists unless you probe or dig and take a look. If you see large wet slab avalanches that have gone to the ground, suspect slopes with similar elevations and aspects probably have a similar structure. The large wet snow avalanche that occurred on an east- southeast aspect below Mt Baldwin in McGee Canyon (easily seen from highway 395) is a good example of the size and destructive potential of a full depth avalanche.

Slopes where free water has not yet percolated to this layer will hold the best potential for these avalanches. The time period when free water percolates into the deeper layers of the snowpack and drainage channels id not well defined though the heat wave near the end of April caused water to drain out of the bottom of the pack, producing the spring runoff for the year. One might expect the possibility of deep wet slab type avalanches is over with the heat wave, but take a look at the large slide under Mt Baldwin. The best rule of thumb in the avalanche forecasting business is that there are NORULESOF THUMB.

Areas where the snowpack rests on top of granite slabs are good places for glide avalanche and wet slab avalanches to occur. The domes in Tuolumne Meadows have wet slab and glide avalanches every spring. The Sonora Pass area also has glide and wet slab avalanches each spring. These events are very difficult to predict and can result in large, destructive avalanches.

Avalanche Concern #3 Storm Slabs and Wind slabs:

The third major concern involves avalanche activity that may occur during and after any late season storms. Expect a period of snowpack instability during the storm itself, then a second cycle of avalanche activity as rapid warming occurs post storm. During the storm, watch for recent avalanche activity, wind loading, collapse, audible whumpfing sounds, and/or shooting cracks. As soon as the sun comes out, new snow will be very sensitive to rapid warming and direct sunlight. New snow will lose strength rapidly as the day progresses causing a significant increase in avalanche danger.

Other hazards such as cornice collapse, moats, glide cracks, and open creeks exist. Stay well back from abrupt edges along ridgelines as human triggered cornice collapse will remain possible during the spring.

Stay out from under cornice areas that are not well frozen, especially if you can see water dripping from the cornice. Areas of weak snow around rocks, vegetation, and along the base of cliff bands exist. Move carefully around these features as the thin bridges of snow could collapse under body weight allowing you to fall into a melted hole next to the feature. Exercise caution when traveling near or attempting to cross creeks as wet snow along the banks can collapse under the weight of a person.

The weekend will be cool with highs in the Mammoth area reaching the low 50’s. Elevations above 10,000 ft will be very cool with highs in the mid 30’s and light northeast winds in the 10-15 mph. Nights at the high elevations will continue to be cold, in the low to mid 20’s.

A warming trend begins on Monday with temperatures expected to reach the upper 60’s in the Mammoth area and low 50’s at higher elevations. Enjoy Spring!!

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Please note that the avalanche danger rating in this advisory expires in 24 hours. This advisory is our best interpretation of snow pack conditions and NWS forecasts issued today. Backcountry travelers should be aware that elevation and geographic distinctions are approximate and that a transition zone exists between upper and lower elevations. Avalanches do not happen by accident and most human involvement is a matter of choice not chance. Most avalanche accidents are caused by slab avalanches that are triggered by the victim of member of the victim's party. Even small slides can be dangerous. Always practice route finding skills and carry avalanche rescue gear. Remember that avalanche danger ratings are only general guidelines. Distinctions between geographic areas, elevations, slope aspects and slope angles should be made.