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Rivers in the atmosphere, big waves in the ocean

In terms of weather, this has been the first real week of winter we've had so far this season. But finally we're getting some action from an atmospheric river, and it is bringing both much-needed rain and the threat of mudslides in mountain regions that were badly burnt just a few months ago.

Graphic showing what atmospheric rivers are and how they affect precipitation

During an El Niño event, the probability of higher-than-average rainfall in California is usually due to what are called Pineapple Express storms. These warm, wet storms occur when the atmospheric river is to the south and picks up and transports water from the tropics. La Niña, which is the counterpart to El Niño, typically results in drier-than-average conditions in California, but when the atmospheric river does come into play it comes from the north and is cold.

We are currently at the mercy of La Niña, and weather forecasters predict these conditions will continue through February and then begin to wane through the early spring. This means that the storms we've had over the past several days have been cold. According to our weather station, on Monday 18 January the high temperature was 24ºC (75ºF), and a week later on Monday 25 January the high was 12ºC (53ºF). It has continued to be chilly throughout the week. Today, Friday 29 January, we're getting a break between storm systems and it's beautifully sunny. Because of the sun it feels warmer, but the actual air temperature probably won't get much higher than it has been already this week.

Yesterday we were hit by what was probably the strongest of the storms in this particular atmospheric river. At the marine lab the waves were routinely splashing up and over the cliffs. When that much water crashes into solid land, the pounding is felt as much as it is heard. After doing my chores I wandered over to Younger Lagoon to see what was going on. I wanted to see if the lagoon had broken through the sand bar.

I spent some time watching the ocean, and this is what I saw:

Storm waves at Younger Lagoon
2021-01-28

That sand bar forms as sand accumulates on the beach during the summer, following the typical sand cycle along the California coast. Younger Lagoon does not drain a river, so there is not a constant flow of fresh water down to the ocean. There is some run-off from the surrounding agriculture fields, but the vast majority of water flowing through the lagoon is run-off from rain. It's that heavy flow of fresh water that sometimes breaches the sand bar and allows water from the ocean to mix with water in the lagoon.

Given how much rain we'd had, I thought it likely that the lagoon would have breached. But as you can see from the video above, it had not. Clearly, there hasn't yet been enough fresh water flow through the lagoon to break through the sandbar.

So we're still waiting for that event. I suspect that once it does, we'll know because of the smell.

In the meantime, the ocean continued to pound the coast. I was wearing my foul weather gear so I went to Natural Bridges to watch the waves slam against the rock formations. That was a fun excursion! The big swells were coming in so fast that the deep BOOM-BOOM-BOOM was almost continuous. Close to shore the water was a constant froth of movement.

Storm waves at Natural Bridges
2021-01-28

You can see how high the waves were hitting against the cliff. The mist blew quite far across the parking lot, and I went home with saltwater drying in my hair. Fortunately I got to spend the rest of the day indoors, drinking tea and keeping dry. Winter storms are great fun, as long as you don't have to be out in them!

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