The Northwest is bracing for a powerful storm system this week that will bring high winds, heavy rain and mountain snow. The National Weather Service says this is the first major hurricane of this season. One atmospheric river And bomb cyclone What makes this storm so powerful – but what do those words mean?
What is an atmospheric river?
atmospheric rivers Snowdrops are no stranger to the western US, especially during the fall and winter months. Atmospheric rivers, or “ARs”, are long, narrow areas of moisture that travel outside tropical regions.
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They are responsible for producing heavy rain and snow, especially when pushed against mountain ranges like the Cascades and Sierra Nevada. A famous type of atmospheric river is called the “Pineapple Express” because it flows through the Hawaiian Islands.
Strong ARs transport water vapor equivalent to about 7.5 to 15 times the average flow of the Mississippi River. Annually, 30% to 50% of the west coast's rainfall occurs with only a few atmospheric river events.
What is a bomb cyclone?
Bomb cyclones are low pressure systems that occur in what meteorologists call “bombogenesis”. Bombogenesis occurs when a mid-latitude cyclone (“mid-latitude” meaning the region between the tropical and polar regions) rapidly intensifies over a 24-hour period.
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In most areas, if the atmospheric pressure drops by at least 24 millibars within 24 hours, it is considered a bomb cyclone.
Bomb cyclones can occur when a cold air mass collides with a warm air mass, causing some significant winter storms.
When an atmospheric river and a bomb cyclone arrive at the same time, a major weather event is expected. Atmospheric rivers provide moisture, and the bomb provides cyclone intensity and increased winds.
This week's major event has brought more than 10-20 inches of rainfall in some places. Mountain snowfall is expected to exceed a foot in most areas; The tall height can go up to 2 to 3 feet.