The sky was clear across much of metro Phoenix, but a tightly wound storm cell arrived with a bang late Monday night.

Make that a couple of bangs — those low rumbles of thunder so rarely heard anytime other than during the Arizona monsoon.

In the big picture, it was all part of the arrival of a “strong upper level open-wave low pressure trough,” according to the more technical version of the National Weather Service forecast. The arrival of a cold front, in essence. The effects were easier to summarize: “gusty winds, cooling and isolated to scattered showers.”

Some of those showers triggered isolated surprise and delight in the west valley Monday evening. As midnight approached, one speck of dark red moved across the radar screen against a field of more subtle greens and blues.

With it came gusts and the spooky rumble of thunder, plus an occasional blinding flash.

“Mostly cloud-to-cloud lightning,” said Travis Wilson, meteorologist with the National Weather Service in Phoenix, where such events trigger interest without undue excitement. Though there was reason for interest.

There was “one strike almost due west of the airport,” Wilson said of the lightning. And the storm itself?

“To have the showers come this far south? No, we weren’t expecting that,” Wilson said. “We’re just watching convection to make sure it doesn’t pick up.”

With the unexpected burst of weather past, the weather service was turning attention toward Tuesday and beyond: slightly cooler temperatures, highs in the 70s and more rain far west of Phoenix. Plus, there is a “red flag warning” for the high winds that come in behind the rain.

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