Coastal California Sees Less Lightning Than Almost Anywhere Else In The US. Here's Why
I love weather. I love thunderstorms. I love them both in spite of, and because of, the thrilling terror that only a Midwestern tornado siren can inspire.
I love them because, in elementary school, after my first time watching Twister, a (perfect) film about a fictional tornado outbreak, my friends and I had to retreat into the basement — to shelter from a real storm, right outside our window.
So after nearly a decade living on the West Coast, I’ve trained myself against getting my hopes up for Real Weather: That rumble outside my window is likely just a dumpster rolling downhill, a firework booming across town or the sound of my dreams collapsing like an oil drum under a tank.
On Wednesday, to my glee, I was wrong: a series of storms rolled through Southern California, bringing actual thunder and lightning to my adopted home. I was so excited that I more-than-half-seriously pitched my editors a story entitled, “So You’ve Never Heard Thunder Before. Don’t Worry — I’m From A Place With Real Weather, And I’m Here To Help.”
They nixed the headline, but they were curious too: Why do we get so little lightning and thunder in L.A.?
Less Lightning Than ‘Almost Any Place On Earth’
I pulled the numbers, and was surprised at how rare these phenomena are here. Within a 10-mile radius of LAX, the National Oceanic and Atmospheric Administration has recorded a grand total of approximately 1,200 cloud-to-ground lightning flashes over the nearly three decades between 1988 and 2017.
By contrast, in Florida — a lightning hotspot — Orlando sees 14,000 strikes in an average year.
“Coastal California sees some of the least lightning of almost any place on earth, actually — and certainly in the U.S.,” said Daniel Swain, a climate scientist with UCLA’s Institute of the Environment and Sustainability, who also has a background in meteorology.
The vast majority of the time, Southern California lacks the ingredients for the storms that spawn thunder and lightning. The clouds that spawn thunder and lightning are the product of warm, moist air rising to soaring heights; most thunderstorm clouds are 20,000 or 30,000 feet tall.
But during the warmest months of the year, Swain explained that air in Southern California’s atmosphere tends to flow downward; it’s the result of high pressure. That’s why instead of June thunderstorms, L.A. gets “June Gloom,” a thin layer of clouds that you can often see from the top of Mount Baldy at nearly 4,200 feet above sea level — well short of the heights these clouds would need to rise to form thunderstorms.
The high pressure “is like putting a lid on a pot,” Swain explained. “You really can’t get that vertical growth of clouds you need to generate summer precipitation like you do elsewhere — because fundamentally, what builds clouds is upward vertical motion, and in California we tend to have downward vertical motion.”
The link between upward motion and storm formation helps explain why scientists record most lightning strikes in L.A. County at higher elevations — in the Angeles National Forest, in the Santa Clarita Valley or the Antelope Valley.
But even the approximately 16,000 strikes recorded in the Santa Clarita Valley over the past three decades pales in comparison with the 201,000 strikes observed near Wakita, Oklahoma — the heart of Tornado Alley, and the spiritual home to some of Bill Paxton’s finest work.
So Why Did LA Hear Thunder On Wednesday?
There were several difference-makers in the air over L.A. on Wednesday. First, a somewhat-unusual flow of monsoonal moisture. Normally, this pipeline feeds summer storms over Arizona, Colorado, New Mexico and Nevada — but on Wednesday morning, the moisture seeped into California.
“It’s rare, but it’s not as unusual as it might seem,” said José Martínez-Claros, a postdoctoral researcher in atmospheric sciences at UC San Diego’s Scripps Institution of Oceanography.
The second ingredient? In Swain's terms, the “lid” came off the “pot” — instead of high pressure, a weak low pressure system set up off the coast. Low pressure favors upward motion in the atmosphere. With upward motion came tall clouds — tall clouds that became storm clouds. With storm clouds came lightning and thunder.
Across the U.S., climate change is likely to produce more extreme weather — including more violent and destructive thunderstorms in the American Heartland. One study even projects that lightning strikes will increase by about 12% for every degree Celsius of global warming.
It’s not exactly clear whether climate change will mean more lightning and thunder in L.A., though.
For the most part, Swain said many of the fundamentals in California’s climate — cold ocean temperatures, high pressure to keep the “lid” on in the summer — will continue to suppress many thunderstorms here. But Swain also said it’s difficult to predict how climate change will affect the region, and even marginal differences could have huge ramifications.
“There are a lot of fires that have been sparked by lightning,” Swain observed, “especially if you go farther north into Central California and the Southern Sierra, where it’s much drier lightning — there’s not much rain falling. In that context, could it matter if we see small incremental increases in lightning during the dry season? It could matter — if it’s true.”
Martínez-Claros said the concern is that climate change will cause more extreme weather events in California, including extreme droughts. Extreme droughts, he said, are often followed by drastic snap-back storms in which a region will get a single year’s worth of moisture in perhaps as little as a single day.
“That means more violent storms concentrated into shorter windows of time,” he said, “which is likely to bring more lightning.”
In other words: It's the extreme.