One phrase has come to mind over the past week (besides “Hawaiian shirt” and “flip flops”): “Melt-Freeze.” Temperatures have been trending ever warmer in the Sierra and turning our former powder into creamy corn snow by mid day on most slopes. The melt-freeze process – with the spring sun warming the snow throughout the day and cold nights refreezing it – generally makes the snowpack more stable over time. Prolonged warming, however, can start to weaken the snowpack on a deeper level. On slopes with tree cover and in rocky gullies where solar radiation doesn’t dissipate as readily as on open slopes, melt water has been saturating the snow down to a foot deep or more. As snow temperatures stay warmer, and water content is higher, loose wet and wet slab avalanches become more likely. Tuesday, South and East aspects warmed early. Surfaces became wet by 11am at elevations up to about 11500’. Slopes also warmed up to alpine elevations. Skiers triggered some small wet slabs at 13000’ on Mt. Tom yesterday. As skies become cloudy this afternoon and into this evening, solar radiation will have an even harder time escaping. Loose wet avalanches may become more widespread and larger, especially near rocks, cliffs, and on slopes with forest cover. Small point releases and roller balls indicate that wet snow is becoming unstable.
Light winds from the south have been cooling the snow at upper elevations. Firm wind board can be dangerous in it’s own way since a slip and fall on steep terrain could make for a long slide down and have higher consequences. Winds are set to be stronger from the southwest today through Thursday morning. This could result in slopes taking longer to soften.
