Thursday, December 2, 2021

Was the cyclone of bombs in California the Big Impact?

The two storms that recently hit Northern California and the Pacific Northwest were extraordinary in strength and historical rainfall. They were also unique because they happened at the very beginning of the season.

But how rare are they? Not surprisingly, in a state known for its extreme weather conditions, California has experienced similar events before. For example, Alex Tardy of the National Weather Service office in San Diego quotes the Columbus Day storm of 1962, also sometimes referred to as the “Big Bang.”

This storm brought torrential rain and strong winds to Northern California. The sixth game of the 1962 World Series on October 11 at Candlestick Park between the San Francisco Giants and the New York Yankees had to be postponed due to heavy rain.

Both storms this month brought heavy rain and strong winds. Both qualify as “bomb cyclones” due to the rapid intensification of low pressure systems, with atmospheric pressure dropping by at least 24 millibars (a measure of pressure) in 24 hours. Generally speaking, the lower the atmospheric pressure, the stronger the storm.

The first storm hit Northern California and the Pacific Northwest on October 21. A second, more powerful storm hit California on Sunday and Monday with a central pressure of 942 mbar, the equivalent of a Category 4 hurricane. The Saffir-Simpson Scale classifies hurricanes based on wind speed and central pressure.

On November 26, 2019, another bomb cyclone caused the lowest pressure recorded in California, 973.6 mbar, in Crescent City. This storm caused a 75-foot wave off Cape Mendocino.

The 1962 storm began in the central Pacific Ocean and escalated into Typhoon Fred off Wake Island on October 3. It proceeded northeast towards the Aleutian Islands and on October 9 lost its typhoon status over cooler waters. The system merged with the cold front to the north. The Pacific Ocean and turned into a so-called mid-latitude cyclone, winding to the southeast, and then rushing to the Pacific Northwest and British Columbia.

Mid latitudes or extratropical cyclones are low pressure systems that typically occur between 30 and 60 degrees latitude in the Northern Hemisphere.

By the time the storm struck off the coast of Oregon and Washington, its central pressure had dropped to 958 mbar. At that moment, the storm was the equivalent of a Category 3 hurricane.

An unusually deep low pressure system and atmospheric river as seen from space on Sunday afternoon.

(NOAA and Los Angeles Times)

The October storms also had a tropical connection, using moisture from the remnants of Typhoon Namteun in the Pacific Ocean northwest of Hawaii. Namtheum scattered west of the international October 19 date line, and was less active than Fred, according to Ian Null, an experienced meteorologist at the Golden Gate Weather Service in the San Francisco Bay Area.

While some experts believe the impact of the former typhoon was small, from October 16 to October 18, it actually contributed to the increase in moisture that entered the atmospheric river, Tardy said. The atmospheric river has reached the fifth level, the strongest.

The 1962 storm was also associated with an atmospheric river, a phenomenon that accounts for up to 50% of rainfall in the western United States. Atmospheric rivers are channels or corridors of water vapor, usually in the lowest layers of the atmosphere at 10,000 feet. They are on average 300 to 400 miles wide and can transport water at the equivalent of 25 Mississippi rivers or 2.5 Amazon rivers per second, according to Marty Ralph, an expert at the Scripps Oceanographic Institute.

A plume of moisture in the atmospheric river rises over the coastal mountains and the Sierra Nevada.

Such plumes of moisture account for up to 50% of rain and snow in the western United States.

(Paul Duginski / Los Angeles Times) #

Atmospheric rivers are sometimes referred to as the “pineapple express”. However, while “all pineapple expresses are atmospheric rivers, not all atmospheric rivers are expressions of pineapples,” said Drew Peterson, a meteorologist for the National Weather Service in Monterey. Pineapple express trains are warm, atmospheric rivers that originate in the Pacific Ocean near Hawaii.

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The recent storms were the result of unusually deep low pressure off the Pacific Northwest coast. “Low levels are the driving force for the strengthening of the atmospheric river,” said Tardy, a San Diego-based meteorologist. “The two things you need are deep moisture in the water vapor in the atmosphere, and you need a strong wind field to form a significant atmospheric river,” he said. “An atmospheric river needs wind transport in the Pacific Ocean; otherwise it’s just moisture. “

The pressure gradient – the difference between high and low pressure areas – also drives the winds.

Tardy explained that there is a lot of moisture in the South Pacific, and the remnants of a typhoon are not necessarily needed to cause heavy rains, atmospheric rivers, or a version of them called the pineapple express. The cyclone with bombs in the Pacific Northwest was also not required for heavy rain, he said, but when it all adds up, this is what happens.

All of this is very unusual to see at this latitude at this time of year, according to Tardy.

Strong winds hit the far side of low cities on California’s northern coast on Sunday, according to Ryan Aylward, a meteorologist at the National Weather Service’s Eureka office. Counterclockwise circulation around the low pressure system means that as a storm such as this one off the coast moves, winds change from south to west and then northwest. Many trees and supports have been felled on the northern coast of California, Aylward said. Sunday’s heavy storm hit the shore, 200 miles west of Seattle, but he said the 1962 storm was much closer to the coast, and its winds did much more damage. Eventually, the storm came ashore on Vancouver Island.

The 1962 storm also caused severe flooding and landslides, especially in the San Francisco Bay Area. Oakland received 4.52 inches of rain in one day and 3.77 inches in Sacramento. Wind damage was widespread from Oregon to British Columbia.

During Sunday’s storm, downtown Sacramento scored a record 5.44 inches in 24 hours, breaking the record set in 1880, according to the National Weather Service. The Blue Canyon off Interstate 80 in the Sierra Nevada northeast of Sacramento received 10.4 inches of rain, also breaking the record.

This year’s storms were unusual for October, but they were providential as well. Because the land was so dry due to the prolonged drought, it soaked up sediment like a dry sponge. Reservoirs have sufficient sediment trapping capacity. “If this were not the case, there would have been a larger flood,” said Aylward. “We’re lucky it happened in October.”

Nation World News Desk
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