Snow surface melt and potential wet slab setup on Donner Pk/Mt. Judah.

We went to Donner Pk/Mt. Judah today to look at both snow surface warming and concerns for a potential wet slab avalanche problem on the remains of the March 24 surface hoar layer.

A strong snow surface refreeze occurred in this area last night. The top 5 to 6 inches of the snow surface had refrozen overnight with below freezing air temperatures and clear skies. Stronger than forecast NE winds were creating significant convective cooling on the ridgetops with little to no snow surface melt occurring there. However, just below the ridgetops, significant snow surface melt was occurring. Even with below average air temperatures, the strong April sun did its work today. On Mt. Judah, wind protected areas on E-SE aspects held deep almost unsupportable wet snow at 8,000' around 11 am (photo 2) with the surface crust fully melted away. Conditions were conducive for loose wet avalanches in steep wind protected terrain from midday onwards. Large chunks of fallen cornice debris, likely from Apr 10 or 11 were present on the E face of Mt. Judah (photo 1).

We dug a snowpit between Donner Pk and Mt. Judah at 7,580' on a N aspect in the vicinity of a snowpit from a few weeks ago where instability associated with the March 24 buried surface hoar (SH) layer had been observed. We found the Mar 24 SH layer about 2 feet below the snow surface. The wetted front of melt water moving down through the snowpack had reached through the top 1 foot of the snowpack with about 1 foot more to go to reach the SH layer. This SH layer is located deeper in the snowpack here than in other areas. Snowpit tests on the SH layer gave results of ECTP 22 & 30. This provides additional concern for a potential impending wet slab problem once free water reaches down to the SH layer.