Spring has been in full swing in the Sierra. The snowpack has mostly consolidated and is characterized by Melt-Freeze crusts separated by rounds or decomposing grains closer to the snow surface. A minor disturbance raced through the northern half of the forecast zone on Sunday night with rain levels up to almost 9,000’ for a short period. Low temperatures were exceptionally mild overnight and the snowpack warmed quickly on Monday. Lows in the 20s Monday night helped set up a good freeze going into the daily melting cycle on Tuesday.
Wednesday, temperatures are forecast to reach well above average. Rocky outcrops, trees, and mostly cloudy skies will trap the heat and reflect in back down onto the snow, elevating the hazard of loose wet avalanches. Large pinwheels or ski penetration of boot top or greater are signs the snow is loosing strength and becoming unstable. Starting early and being out of steep, rocky terrain before things get too warm is the best strategy for avoiding loose wet avalanches.
Winds will be moderate and gusty as the ridge that has been dominating our weather pattern for the past several days begins to push east. On Thursday, winds will increase with southwest flow aloft as an unusually late Atmospheric River storm makes its way towards the California coast. Small Wind Slab avalanches may become possible Thursday evening depending on the timing of an incoming storm. 1-3” of snow are forecast overnight on Thursday with most accumulation expected after midnight. Predicting the timing and snow levels for spring storms can be tricky, so pay attention to changes and trends if you plan to be out after dark.
Wednesday and Thursday morning, and as winds cool the snow surface during the day, firm, slide-for-life conditions will exist. Be careful of your exposure to a slip and fall on steep terrain where consequences are high.
