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The Pacific Northwest is preparing for a significant storm system predicted to sweep through the region this week, bringing with it strong winds, substantial rainfall, and mountain snow. According to the National Weather Service, this event marks the first major storm of the season. This storm is notable due to the presence of an atmospheric river and a bomb cyclone, both of which are key to its intensity. But what exactly do these terms entail?
Understanding Atmospheric Rivers
Atmospheric rivers (ARs) are familiar phenomena in the western United States, particularly during the fall and winter months. These are long, narrow corridors of moisture that migrate outside of tropical areas.
Atmospheric rivers play a crucial role in generating heavy precipitation, particularly when they encounter mountain ranges like the Cascades and Sierra Nevada. A well-known example of an atmospheric river is the “Pineapple Express,” which draws moisture from the Hawaiian Islands.
Powerful atmospheric rivers can carry water vapor equivalent to 7.5 to 15 times the typical flow of the Mississippi River. In fact, it is estimated that 30% to 50% of the annual precipitation on the West Coast originates from just a handful of these atmospheric river events.
The Mechanics of Bomb Cyclones
Bomb cyclones are a type of low-pressure weather system that undergo rapid intensification through a process known as “bombogenesis.” This phenomenon occurs when a midlatitude cyclone experiences a significant drop in atmospheric pressure within a 24-hour period.
Specifically, a storm is classified as a bomb cyclone when the atmospheric pressure declines by at least 24 millibars within that same time frame. These storms typically arise from the interaction of cold air masses with warm air masses, often leading to the development of severe winter storms.
The convergence of an atmospheric river with a bomb cyclone results in a significant weather event. The atmospheric river contributes the necessary moisture, while the bomb cyclone injects intensity and heightened winds into the system.
This week’s anticipated storm is projected to generate rainfall amounts exceeding 10 to 20 inches in various locations, with mountain snow accumulations expected to surpass one foot in many areas. In higher elevations, totals could escalate to between 2 to 3 feet.
Additional Insights
As meteorologists closely monitor this developing weather situation, the widespread impacts of such a storm highlight the importance of preparedness, particularly for those in vulnerable regions. Understanding the interplay between atmospheric rivers and bomb cyclones is crucial for anticipating potential hazards associated with extreme weather events.
Source
www.cbsnews.com