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The blast was so powerful it apparently blew the woman's clothes off her body. A char mark was visible on the trunk of the tree.
Witnesses said she may have been walking to the Metrolink station after work when all of a sudden, they heard two loud explosions.
"It was a very significant blast of electricity, caused a very devastating wound to her neck and torso, blew out the bottoms of her shoes and also blew out almost all the clothing on her top as far away as 30 feet," said Sgt. Jeff Decker.
Neighbors set up a memorial next to the charred tree.
There were hundreds of lightning strikes throughout San Bernardino County on Wednesday.
The same turbulent weather triggered a lightning strike that hit a jet in Northern California.
The SouthWest Airlines plane, with 53 passengers on board, had just taken off from Oakland on its way to Burbank.
No one was hurt, but the pilot returned to Oakland as a precaution so that the plane could be inspected.
Wednesday's wild weather took the life of another woman in the San Bernardino Mountains when a strong gust of wind blew a tree on top of a suburban. The tree crushed the suburban.
The woman was identified as 31-year-old Elena Martinez of Big Bear Lake.
Strong winds blew trees over all over the Southland, including a huge tree in Arcadia.