Snow began falling in the Leavitt Lake area yesterday –this morning there is 10 inches of snow at Leavitt Lake. Snowfall is picking up over the forecast area with 4 inches of snow recorded on the Mammoth Pass snow pillow and two inches of new snow at the June Mountain weather plot. The storm is just now reaching the area and heavy snowfall is expected later this morning.
As new snow accumulates later today, the primary avalanche concern is storm slab avalanches. Winds are from the west southwest this morning but be aware that northeast winds are blowing on the north facing slopes at the top of Mammoth.
Storm slabs are soft cohesive layers of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems will last through Friday. Storm slabs are most dangerous on slopes with terrain traps – gullies, couloirs, over cliffs or other terrain features that make it difficult for a rider to escape off the side. The most sensible way to reduce your exposure to avalanche risk is waiting a day or two after a storm before venturing into steep terrain. Of course most people do not wait so it’s up to you to be alert for nature’s warning signs- cracking, whumpfing, wind loaded slopes, recent avalanches and on going wind loading.
The second avalanche problem is the weak, lousy snow structure that will get stressed today as the storm intensifies. I do not know if there will be widespread instability within this old layer but avalanches triggered on the old weak snow could be large. Areas to watch out for are thin rocky areas adjacent to thick denser wind loaded snow and where shaded sub alpine slopes roll over abruptly- the places where it’s easy to get some air. If you are traveling on flat ground in meadows and whumpfing occurs, treat slopes above you with great caution.