Variable spring weather continues with warm periods interrupted by fast moving, colder storms. The most recent disturbance to pass through our area deposited almost a foot of new snow at upper elevations around the Mammoth area, and around 6” at middle elevations. Strong to moderate SW winds were blowing and soft wind slabs were observed on Monday afternoon. The new snow was very soft and unconsolidated sitting atop a thick, hard melt-freeze layer from earlier in the month. The new snow has not yet bonded well to the underlying crust and loose sluffs were easy to trigger throughout the storm. Temperatures in the low teens and single digits Monday night will have slowed the bonding process for both wind slabs and the loose storm snow.
Quiet weather on Tuesday may allow wind slabs in the upper elevations to slowly heal, but the intense spring sunshine and warmer temps may initially make wind slabs more sensitive. That same warming trend Tuesday may melt some of the loose surface snow and create a loose wet avalanche hazard as well by the warmest part of the day. By Wednesday, with increasing cloud cover and renewed winds, the loose wet problem may improve. However, if there is still loose snow available for transport, new wind slabs my form by Wednesday afternoon.
These periods of frequent change make forecasting challenging over a 48 hour period. The important thing to remember is what to look for in terms of instability. For wind slabs: steep slopes with recently drifted snow near and above treeline are suspect. These drifts can look rounded or pillow-shaped and will most likely be found below ridgelines and on the sidewalls of gullies. Denser snow that cracks around you is a direct sign of instability. For thawing problems: wet snow at the surface heralded by rollerballs or small sluffs is a good clue. Slopes receiving the most solar radiation, especially at middle and lower elevations near rocky or vegetated areas will be of most concern. Since the warming follows the sun across the sky, from E-S-W facing slopes, you can time your day to avoid loose wet avalanches. By the time the surface snow is saturated you should move to shadier, less steep slopes.
