Rain and lightning in the Bay Area forecast: Is this normal?


A major monsoon wave will bring a mix of wet and dry thunderstorms to California this week, increasing the risk of wildfires at a time when several large flames are already torn across a parched landscape.

While there is a high chance of thunderstorms in the Sierra Nevada, the probability of the San Francisco Bay Area is slight even if the risk is high, the National Weather Service said.

“It takes just a spark to start a wildfire,” said Geri Diaz, a forecaster with the weather service.

The highest chance for storm activity in the Bay Area is Monday afternoon through Tuesday morning.


The moisture plume brought a rampage of thunderstorm activity over Las Vegas Sunday night and brought down over Southern California Monday morning, the weather service said. Today, he will rotate north in a clockwise motion, move along the coast and then push back inside.

“It’s still a bit of a chance,” Diaz said. “It nails down to how much of that moisture makes it up north. It can also be hard to predict since we have a marine layer today. The marine layer brings in that low fog … the infamous San Francisco fog. It is a very stable air mass It helps protect the area against thunder There is the opposition that if you have enough moisture then it can override the sea layer.Storms would form above the sea layer. that’s what we mean when we talk about high convection, thunderstorms that are high in the atmosphere. “

Lightning in the summer can often strike without any rain, and dry lightning is particularly concerned, as it increases the risk of fire fires starting. This incoming system has a lot of humidity associated with it and rain occasionally is possible.

“It may be initially dry lightning and it seems that we may have enough moisture too for some rain to fall later on,” Bingaman said. “Another thing to consider is even if we have wet storms, lightning can hit several miles away where the rain is falling. That’s another situation where it could be lightning dry.”

There may also be scattered throughout the day on Monday ahead of reaching feather moisture.

“We have enough moisture in the air that we could get a few cells to develop ahead of the moisture pen,” Diaz said.

Monsoon refers to a seasonal reversal of wind patterns over a region and the summer monsoon is associated with an increase in thunderstorm activity and in North America wind pulls moisture from the Pacific Ocean and the Gulf of Mexico and transports it to the Southwestern United States.

“The summer monsoon is indeed a normal, if somewhat sporadic, feature of California’s summer climate (especially mountains and deserts),” Daniel Swain, wrote on Twitter. “It’s more pronounced in the southwestern interior, like Arizona and New Mexico, where heavy summer rains occur every year.”

Sometimes the humidity pushes north of California.

In the past year, awareness around summer monsoon rides and storms has increased due to the August 2020 lightning event that sparked thousands of fires and led to a record-setting year of wildfires in California.

Weather service forecaster Roger Gass said the number of major wildfires started with those affected by them in 2020 and recent years have left people “more worried and anxious” when storms enter the forecast. Has it led people to wonder if storms are becoming more common?

Gass said the data on lightning activity is lacking, but he has a general sense of what is typical based on his local knowledge and experience.

“Overall, lightning is less common in all Bay areas given much of our defined weather in the marine environment that does not have enough instability to produce thunder,” he said. “We typically need a strong cold front, winter system, and or all the right components to align for thunderstorms during the summer months. The August 2020 event was uncommon to provide the amount and widespread protection of lightning strikes. However, not completely unusual in .All the right ingredients must be aligned for such an event and therefore occur much less frequently / infrequently. In addition, there is no indication that events like these are becoming more frequent at this time. “

Lightning is most common in the Sierra Nevada due to the lack of marine layers and mountainous terrain where air masses are forced to rise, intensifying storms.

This week’s lightning event is expected to be far less extreme than the one in 2020.

“The August 2020 event also had tropical humidity,” Brooke Bingaman, a meteorologist with the weather service, said. “We were dealing with monsoon moisture and the remnants of a tropical hurricane in 2020. We don’t see that this time.”

While the Bay Area weather service office posted on Twitter that the biggest chance of thunderstorms in the Bay Area is in North Bay, Bingaman said the entire region should be prepared.

“Personally, I feel like in these situations the main thing to remember is the ingredients seem to be coming from the Bay Area,” he said. “If it was me, I’d want everyone on the alert.”

He added: “These types of forecasts are difficult. The monsoon moisture can enter our area and we don’t know whether it will stay more sea or or come ashore. Plus, we have our marine layer that would “It’s a … low-probability situation, but big impact if it happens.”

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