A so-called atmospheric river is bringing massive amounts of tropical moisture to California, prompting weather forecasters to issue alerts for higher risks of flooding.
Atmospheric rivers are channels that form in Earth’s atmosphere And water vapor funnels from typically moist tropical regions into dry regions away from the equator. These channels can transport huge amounts of water within a short period of time, causing deluges when they make landfall.
The type of atmospheric river that threatened California on Wednesday and Thursday (Jan. 4 and Jan. 5) is a phenomenon that appears regularly. It is sometimes called the Pineapple Express, usually in reference to the fruit grown in Hawaii where this river originates.
The current atmospheric river has combined with an area of low pressure that circulates over the Pacific Ocean, together forming a powerful storm that threatens usually sunny conditions.
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Satellites of the US National Oceanic and Atmospheric Administration (NOAA) are monitoring the weather system, revealing various aspects of it including wind speed and expected amount of rain.
NOAA Weather Prediction Center (WPC) has issued a Medium Risk Alert For extreme rain over portions of the California coast Wednesday and Thursday morning.
“The associated heavy rains will create many areas of flash flooding,” the WPC said in a statement. Statement (opens in new tab), “In addition, multiple streams could cause flooding, potentially affecting larger rivers.”
The WPC said that in areas of higher elevation, such as in the Sierra Nevada Mountains, the rain will turn into heavy snow.
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this is not the first Atmospheric river to hit California recently. On the last day of December, a similar channel dropped a record-breaking 5.46 inches (14 cm) of rain over downtown San Francisco.
The WPC said the current storm system threatens to dump more than 1 inch (2.5 cm) of water per hour on already-soaked ground, raising concerns that mudslides could occur in the mountainous landscape in the area.
according to Washington Post (opens in new tab)San Francisco received more than 11.6 inches (29 cm) of rain in December. That’s more than double the December average for the city, which is 4.76 inches (12 cm).
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