Fires, heat waves, thunder and lightning. What’s going on with California’s weather?

Multiple wildfires are burning across the state, and some are inducing tornadoes. There’s record heat and rolling blackouts. And everyone is stuck at home because of the COVID-19 crisis.

KCRW talks with UCLA climate scientist Daniel Swain about why this extreme weather is happening, and whether this kind of heat and humidity should be expected every summer in Southern California. 

KCRW: What’s going on in California? 

Daniel Swain: “It really is a confluence of multiple extreme events occurring simultaneously throughout the state. The backdrop is essentially a record-breaking prolonged heat wave that's been going on now for over a week in some places, and has broken a number of long-standing temperature records, both in Northern and Southern California near the coast and even in the inland deserts. 

Death Valley hit 130 degrees this weekend. So the backdrop of all of this is extreme heat over a relatively prolonged period. What happened next was over the weekend, a very unusual system of thunderstorms brought thousands of lightning strikes to Northern California, centered actually on the San Francisco Bay Area in particular. 

And since that time, dozens – if not more — of brand new wildfires have sprung up in the wake of that lightning storm. Some of these fires last night made really unbelievably large runs in the Santa Cruz Mountains in the hills east of Napa, and are now threatening populated areas really in almost every corner of the Bay Area.”

Did these storms come with rain, and why didn't that help abate some fires? 

“The big problem with the lightning that occurred this weekend in Northern California is that much of it was dry lightning. Dry lightning just means that you have a thunderstorm with cloud-to-ground lightning that can spark fires, co-occurring with either very little or no precipitation at all. 

There were some thunderstorms in Northern California that produced wind, lightning, even heat bursts, but very little precipitation. In some of the places that did see a couple of downpours from those thunderstorms, it was so hot before and after the storms rolled through that some of the smoldering underbrush that otherwise might have been extinguished by more significant rainfall managed to spring to life when the winds picked up, and became full-fledged fires.”

We saw incredible images near Reno of what is being described as a firenado. What is a firenado? 

“That event occurred even before this weekend's thunderstorms in the Bay Area, but I think it was fair to call it a firenado or a pyro tornado. It was a result of a very intense pyrocumulus cloud, which is really a fire plume that takes on the characteristics of a regular old thunderstorm. It's sort of like a hybrid type of cloud that only occurs when there's a strong heating source near the surface. So a big fire can serve as that heating source. 

And in the case of a large fire vortex like we saw on the Loyalton Fire up by Reno, essentially what you need is a tall pyrocumulus cloud that has a very strong updraft from the heat in the fire. [It] begins to rotate either because the ambient wind conditions are favorable, or because the local topography forces that cloud to rotate a bit. As it begins to spin, it can elongate, and sometimes that spin can come back down all the way to the ground in the form of a large fire vortex.”

The air quality in Southern California is the worst it's been in more than 10 years. Are the fires and humid heat contributing to this?

“Yes, it absolutely is. In general, you need two things for really bad air quality in Southern California. You need [a] strong high pressure system, which sort of keeps a lid on the atmosphere, and prevents all the pollutants near the ground level from mixing out and blowing away. You also need a lot of sunlight and heat. Unfortunately, this kind of weather pattern is conducive for both of those things to be greatly elevated. So throughout California, air quality is quite poor right now. In Northern California, it's mainly poor because of the fires. In Southern California, it's a combination of the heat wave and some smoke.”

Why is this a humid heat wave? 

“This past weekend there was a plume of atmospheric moisture that got sheared off of a decaying tropical storm in the eastern Pacific Ocean. That got caught up in southerly flow over the ocean, [and] that essentially provided a direct pipeline for this moisture to California. That's why we've been seeing the mountain, desert, and even coastal thunderstorms in some parts of the state. It's also the reason things have been so incredibly humid. There's that moisture moving in from the south and east.”

Is this hot and humid weather something we should begin to expect every summer in Southern California? 

“There are two components to it. One is that yes, we know that the frequency and intensity of heat waves in California — and elsewhere — is increasing due to global warming. So the rising temperatures and the increasingly extreme temperatures during heat waves are consistent with that. The humidity question is a little bit different, and I don't have an immediate answer to it right now. It's a plausible hypothesis, but I think it's something we're going to have to take a closer look at.”

When do you expect this heat wave to abate?

“I think there may be a little bit of relief as early as today and tomorrow. The next couple of days will be probably cooler than the past few before it. But then there's hints that next week it's going to heat right back up again, maybe not quite to the levels we just saw ... but quite hot and well above average nonetheless. And that's not great news from a wildfire or air quality perspective in California. Really there's no major relief on the horizons. Next heat wave next week may even be another humid one, which is pretty unusual to have two back-to-back heat waves like that in California.”

— Written by Erin Senne and Amy Ta, produced by Brian Hardzinski and Nihar Patel