2022 United States

Lightning Report

As Californians awaited the first day of summer, they were also bracing for a significant storm system to roll through the state, fueled partly by monsoonal moisture and partly by a disturbance in the jet stream moving across the region. Although the thunderstorms in the forecast were expected to produce very little rain, meteorologists warned they could still produce dangerous lightning.

While there is no such thing as safe lightning, so-called “dry lightning” (i.e., lightning accompanied by rain that evaporates before it hits the ground) is especially dangerous because it brings heightened wildfire risk. And, in drought-stricken California, that risk is already high enough without lightning.

When the storm system finally hit, from June 22 to June 23, it produced more than 208,000 total lightning pulses across the state, including more than 33,000 cloud-to-ground pulses. It was the most lightning the state had seen in a single day in nearly five years.

Wildfire Today reported that the storm did, in fact, ignite a number of small fires. The largest of these was the Thunder Fire, which burned about 2,500 acres before being fully contained. Fortunately, firefighters were able to contain most of the fires without too much difficulty, limiting the total burn area to less than 4,000 acres.

While no amount of destruction is ever good, Californians were fortunate that this incredible amount of lightning did not produce a more incredible amount of fire. For comparison, in August 2020, a similar “dry lightning” storm ignited more than 650 wildfires across northern California, including the August Complex Fire, which became the largest fire in state history. Together, those fires burned an estimated 1.5-2.1 million acres (about the area of Connecticut).

Three factors combined to prevent the outcome of the June 2022 lightning storm from being much worse:

1. Rain is thought to have reached the ground along with some of the strikes, especially at higher elevations.
2. The active North American Monsoon winds brought high relative humidity to the region, making fuels less receptive to ignition.
3. June is still early in the fire season, before fuel moisture drops to critically low levels.

After striking the Florida coastline on September 28, Hurricane Ian took the lives of more than 100 Floridians, making it the deadliest tropical storm to hit the state since the Great Labor Day Hurricane of 1935.

The devastation was made worse by the fact that Ian went through a period of rapid intensification only hours before hitting the coastline. Over a three-hour period, Ian’s wind speeds increased from 120 mph to 155 mph as measured by AEM’s weather network – leaving it only a few miles per hour short of the most dangerous Category 5 classification on the Saffir-Simpson scale.

Ian was unusual in other ways too. Hurricanes typically don’t produce prolonged lightning activity in and around their eyewalls. Ian did. As the storm approached and struck Florida, AEM’s network of weather stations and lightning sensors recorded no less than 98,176 lightning flashes and 839,858 lightning pulses over 48 hours.

There’s an interesting connection between Ian’s unusual lightning activity and its exceptional strength. Both are tied to a process called eyewall replacement.

It’s a natural part of the hurricane lifecycle for the eyewall to weaken over time. As this happens, a new ring of wind and rain will sometimes contract inward and surge upward to replace the old eyewall. This upward surge can enable the clouds to get tall enough at a fast enough rate to temporarily develop ice crystals in them, and those colliding crystals can generate the static charge needed to produce lightning. Unfortunately, this inward and upward movement also causes the new eyewall to spin even faster (like a figure skater pulling their arms inward).

As a result, surges in lightning activity in the storm’s inner core and eyewall tend to be associated with periods of rapid intensification. And that’s exactly what we saw happen with Hurricane Ian. Just before the storm made landfall in Florida, we saw a spike in lightning activity accompanied by a period of rapid intensification.

On the afternoon of November 17, residents of northwestern New York found themselves pummeled by snowfall – at some points, more than three inches per hour. By the time the clouds finally cleared on November 18, some areas had been blanketed with more than six feet. The city of Buffalo more than doubled its previous record for maximum snowfall in a day, and the town of Orchard Park broke the state record for most snowfall in a 24-hour period.

But this storm delivered more than just record-breaking snowfall. It delivered a rare lightshow of more than 1,000 lightning pulses in 24 hours.

Thundersnow, as it is called, is a relatively rare occurrence. It’s been estimated that thundersnow accounts for less than 0.1% of all U.S. snowstorms. The reason for the rarity is that lightning and snowstorms are generally caused by very different atmospheric conditions.

Lightning is caused by conditions of atmospheric instability in which warm air rises rapidly into the cooler air above it. In contrast, most snowfall is generated under conditions that tend to produce atmospheric stability, namely, the air near the ground being almost as cold as the air above it. For comparison, a typical thunderstorm has air rising at more than ten miles per hour, while the most severe snow bands tend to have air rising at only two miles per hour.

However, some snowstorms, such as lake effect snowstorms, can form when cold air near the surface is heated while moving over relatively warm waters. If the air above the surface is cold enough, the newly warmed layer of air can rise rapidly, producing a tall column that looks more like a thunderstorm cloud than a flat snow cloud. That same scenario can produce the atmospheric instability needed to generate lightning; that’s when our snowstorm becomes thundersnow.

Unfortunately, the same atmospheric instability that gives rise to thundersnow also tends to result in heavier snow and higher snowfall rates. Wherever you see thundersnow, there’s a high probability for significant snow accumulation – just as they experienced in northwestern New York.