California’s deadly storms have devastated the state in recent weeks, claiming at least 17 lives and placing tens of millions of people on flood watch.
Since Christmas, parts of the state have received up to a meter of rain and more than 10 meters of snow.
Over the past month, the Sierra Nevada mountains have reached the average amount of snow they receive in a year. This is the most snow the region has seen in such a short time since the winter of 1982-83.
So what causes this historic rain?
extended jet stream
Blame an extremely long jet stream over the Pacific Ocean, stretching from Southeast Asia around Thailand to California.
A jet stream is a column of air blowing at 100 to 250 miles per hour in the upper atmosphere, 4 to 8 miles above the earth’s surface.
MORE: More than 33,000 without electricity when storm hits California
Jet stream helps develop and transport storm systems and water vapor around the world.
This jet stream has been positioned this way for the last 3 weeks.
“The Pacific Jet is unusually south this winter, between 30 and 40 degrees latitude, rather than 40 to 50 degrees latitude,” said Alex Tardy, a coordinating meteorologist with the San Diego National Weather Service.
Additionally, the water temperature is currently 1-2 degrees Fahrenheit above normal just north of Hawaii. This means that there is more latent heat release from the ocean, more water evaporation.
As the jet stream passes over this warmer water, it picks up and carries these extra water molecules to the west coast of the United States, possibly helping to generate extra precipitation, said climate scientist Daniel Swain of the University of California, Los Angeles.
Effect on precipitation
Due to the warming climate, the warmer atmosphere can hold more water vapor (moisture). The more water vapor in the atmosphere, the heavier the precipitation can be when it falls to the earth in the form of rain or snow.
In fact, “Global water vapor increased 10% in extreme precipitation events, which doubled the probability of flooding per century, which occurs every 50 years,” he said.
California storms wreak havoc: How does an extended jet stream affect deadly weather? Originally published on abcnews.go.com