Deep persistent slab avalanches are capable of destroying infrastructure and are usually unsurvivable for those who are caught. Formation of a snowpack conducive to deep persistent slab avalanches is typically driven by meteorological conditions occurring in the beginning weeks to months of the winter season, and yet the avalanche event may not occur for several weeks to months later. While predicting the exact timing of the release of deep persistent slab avalanches is difficult, onset of avalanche activity is commonly preceded by rapid warming, heavy precipitation, or high winds. This work investigates the synoptic drivers of deep persistent slab avalanches at three sites in the western USA with long records: Bridger Bowl, Montana; Jackson, Wyoming; and Mammoth Mountain, California. We use self-organizing maps to generate 20 synoptic types that summarize 5899 daily 500 mbar geopotential height maps for the winters (November–March) of 1979/80–2017/18. For each of the three locations, we identify major and minor deep persistent slab avalanche seasons and analyze the number of days represented by each synoptic type during the beginning (November–January) of the major and minor seasons. We also examine the number of days assigned to each synoptic type during the 72 h preceding deep persistent slab avalanche activity for both dry and wet slab events. Each of the three sites exhibits a unique distribution of the number of days assigned to each synoptic type during November–January of major and minor seasons and for the 72 h period preceding deep persistent slab avalanche activity. This work identifies the synoptic-scale atmospheric circulation patterns contributing to deep persistent slab instabilities and the patterns that commonly precede deep persistent slab avalanche activity. By identifying these patterns, we provide an improved understanding of deep persistent slab avalanches and an additional tool to anticipate the timing of these difficult-to-predict events.

中文翻译：

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美国西部与深部持续平板雪崩有关的天气大气环流模式

深深的永久性平板雪崩能够破坏基础设施，通常对于那些被俘的人来说是无法生存的。通常在冬季开始的几周到几个月内发生的气象条件会导致形成有利于深部持续性平板雪崩的积雪，但是雪崩事件可能要在几周到几个月后才会发生。虽然很难预测释放深层持续性平板雪崩的确切时机，但雪崩活动的发生通常先于快速变暖，强降水或强风。这项工作调查了美国西部三个地点的深部持续性板状雪崩的天气成因，这些记录已有很长的记录：蒙大拿州的布里奇·鲍尔；怀俄明州杰克逊；和加利福尼亚的猛Ma山。 毫巴1979 / 80–2017 / 18年冬季（11月至3月）的地理高度图。对于这三个位置中的每一个，我们确定主要和次要的深层持续平板雪崩季节，并分析主要和次要季节开始（11月至1月）期间每种天气类型代表的天数。我们还检查了对于干板和湿板事件，在深部持续平板雪崩活动发生之前的72小时内分配给每种天气类型的天数。这三个站点中的每个站点在主要和次要季节的11月至1月以及深度持续平板雪崩活动之前的72 h期间内，分配给每种天气类型的天数都有独特的分布。这项工作确定了天气尺度的大气环流模式，这些模式导致了深部持久性板坯的不稳定性，以及通常在深部持久性板坯雪崩活动之前发生的模式。通过识别这些模式，我们可以更好地了解深部持久性平板雪崩，并提供了一种额外工具来预测这些难以预测的事件的发生时间。