Avalanche Science Weekly News
Snow refresh this weekend!
It has been two weeks since the last significant precipitation event in our area. A rain even left us with a widespread rain crust at most elevations. Fortunately, another storm precipitated 10-15 centimeters of snow that enable very sweet turns last weekend at Mores Creek shady aspects.
Last Sunday warm temperatures produced a "cruel" melt crust at all aspects with solar radiation. Skiing took turns from instructional to a "fear-factor" quality reality show if you dared to seek sunny slopes.
Diurnal cycles with the incursions into temperatures significantly above 0-Deg-C, not only facilitated crust formation, but has also favored sintering and settlement of the snowpack while destroying gardens of “near-surface facets” and “surface hoar”. Diurnal cycles with the incursion into the temperatures significantly above 0-Deg-C, not only facilitated crust formation, but has also favored sintering and settlement of the snowpack while destroying gardens of “near-surface facets” and “surface hoar”.
By last weekend no evidence of instability could be found at mid to bottom snowpack structures. Moderately reactive rounded facets sandwiched between the crust and melt-freeze layers can be found at the 30-35 cm depth.
The great news is that tonite we are entering a storm cycle that promises to cover Mores Creek Summit with 30+ cm of snow by early next week. Snow amounts for Saturday are in the 5-10 cm, but by Saturday night the precipitation intensity increases with a potential of 25 cm by Sunday morning. Winds reach moderate level (> 7 m/s) by Sunday morning.
Saturday planning should incorporate the selection of ski terrain where isolated pockets of the persistent slab at the 35 cm depth are avoided. The use of quick pits are the best tools to identify their presence of these persistence slabs distributed at isolated and protected deep north aspects. If precipitations totals by Saturday remain below the 10 cm, it is unlikely to observe dry-loose or storm-slab reactivity from new snow.
By Sunday, the avalanche risk landscape changes. The significant new snow and moderate winds forecasted at Mores Creek Summit will require the ski touring plans to incorporate wind-slab and storm slab avalanche.
This weekend storm is characterized as a ”warm storm”, with snow levels between 5,500-6500 feet. It is possible that snow transported snow will be limited, particularly considering the topography of Mores Creek Summit, thus the wind slab avalanche problem will be limited to higher elevations and ridge tops between the 7600 and 8100 feet.
Warm storm favors the formation of cohesive slabs. The bonding of Saturday’s storm snow with the old, crusty, complex heat basked surface will be critical for Sundays Storm avalanche problem sensitivity. If Saturday’s snow fails to bond to the old snow surface, the elements of an avalanche instability cycle will be in place with a slab undermined by precipitation particles resting in a melt-freeze slick surface.
Check AVYSCIENCE.COM blog for an update on Mores Creek Summit this next Saturday, February 2, 2019.
Author: Chago Rodriguez