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Rain on Snow (ROS) events occur when rain falls onto an existing snowpack and freezes, forming an ice crust that can have severe consequences to wildlife, infrastructure, and communities. As the Arctic continues warms faster than ever before, it is predicted that ROS events will become more severe and frequent.

Rain on Snow Events

Rain on snow events occur when rain falls on top of existing snow cover. This phenomenon can create a glaze layer of ice, leading to various environmental and safety impacts. Understanding these events is crucial for mitigating their effects on both human activities and wildlife.

What Are Rain on Snow Events?

Rain on snow events happen when warm, moist air moves over a snow-covered surface, causing rain to fall. When the rain contacts the cold snow, it can freeze, forming a layer of ice. This glaze layer can vary in thickness and extent, depending on the intensity and duration of the rain, as well as the temperature of the snow and air.

How Do Rain on Snow Events Happen?

Several factors contribute to the occurrence of rain on snow events:

  1. Weather Patterns: Warm fronts or atmospheric rivers can bring moist, warm air over cold, snow-covered regions.
  2. Temperature: The air temperature must be above freezing to produce rain, but the snow surface temperature must be below freezing to allow the rain to freeze upon contact.
  3. Snowpack Condition: The existing snowpack's temperature and structure influence how the rain interacts with the snow.

Impacts of Rain on Snow Events

Rain on snow events can have significant impacts on both human activities and wildlife:

Safety Impacts

  • Slippery Roads: The glaze layer of ice can make roads extremely slippery, increasing the risk of accidents.
  • Infrastructure Damage: The weight of the ice can damage power lines, trees, and buildings.

Environmental Impacts

  • Wildlife: Animals such as caribou and reindeer can struggle to feed, as the ice layer prevents them from accessing the vegetation beneath the snow.
  • Hydrology: The ice layer can alter the natural melting process of the snowpack, affecting water runoff and potentially leading to flooding.

Rain on snow events are complex phenomena with far-reaching impacts. By understanding the conditions that lead to these events and their potential consequences, we can better prepare and respond to mitigate their effects on both human and ecological systems.

ROS ice layers among reindeer. Image courtesy of the National Snow and Ice Data Center (image credit to Florian Stammler). This image shows multiple ice layers formed as a result of two ROS events in November 2007 on the Yamal Peninsula in Siberia, Russia.
Florian Stammler