There were seven confirmed tornadoes across the Phoenix area in 2019, the most since 1972, according to the National Weather Service in Phoenix.

"That’s something I would say is a once-in-a-generation sort of thing," Marvin Percha, a weather service meteorologist, told The Arizona Republic on Tuesday. The data goes back to 1950.

The weather service shared the information Tuesday as an update to the news that three tornadoes touched down in metro Phoenix one Friday morning in November.

Why doesn't Phoenix usually have tornadoes, and why did we in 2019?

Tornadoes are a rare event in the Phoenix area because the area doesn't generally have both of the ingredients required to whip up a tornado: unstable air mass and wind shear, which occurs when the wind's speed or direction or both change with height.

"It's tough to get that around here. In the summer we have instability but we don’t have wind shear. In the winter we have kind of opposite, strong winds but don’t have the instability. It's something that has to come together and in our part of the country that doesn’t happen very often," Percha said.

While it is not clear why so many happened in 2019, Percha said climate change did not play a role.

"Climate change is kind of a long term thing; this is kind of what we call ‘weather,’ a short term thing. Historical data says it has happened before so it really – at this point, to speculate global warming would be really completely incorrect," Percha said.

2019 tornadoes were all weak

All of the tornadoes that hit metro Phoenix in 2019 were considered weak, ranking as either F0 or F1 on the Fujita scale, which is used to rate tornado intensity.

"Most tornadoes drop down in open desert, maybe pull a tree down, take some roofs off, but the vast majority of them here are quite weak," Percha said.

The record still sits with 1972 and 2019 is in second place, but here are the other years metro Phoenix has seen the most tornadoes since 1950:

Five tornadoes in 1992.

Five tornadoes in 1993.

Four tornadoes in 1971.

Percha said the Phoenix area likely won't see as many tornadoes in 2020.

"Statistically, it would be highly unlikely that it would repeat again this year," he said. "It takes such a rare combination of things for tornadoes to happen in the Valley here in the first place."

1972 also saw Phoenix area's biggest tornado

In 1972, there were 10 tornadoes in the Phoenix area. One of them was the largest on record for the Valley.

On June 21, 1972, a tornado designated as F2 ripped through Scottsdale, Paradise Valley and east Phoenix.

A front-page story on The Arizona Republic the next day said about 200 homes were damaged in Paradise Valley.

It caused extensive damage to canals and power lines, and, at the time, Arizona Public Service Co. officials said the damage was the most severe that APS had ever experienced.

Scottsdale officials initially estimated its public and private damage at $46 million but later revised the figure down.

The tornado was such a rare occurrence and the damage so severe that it drew thousands of sightseers to the area, hindering cleanup efforts, according to a June 26, 1972, story in The Republic.

On that same day in 1972, another tornado struck Eloy about an hour drive southeast of Phoenix.

“Estimated damage would reach at least $1 million from the 15 minutes on Wednesday afternoon during which a black, twisting funnel cloud, followed by 0.69 of an inch of rain passed over the farming community,” a Republic story from June 23, 1972, said.

Reach the reporter Kaila White at kaila.white@arizonarepublic.com or on Twitter @kailawhite.