Martin Zapalac, 41, of Winlock, said the motorcyclist had just passed him on Interstate 5 near the town of Chehalis when he was struck by a lightning bolt, The Seattle Times reported Thursday.
The motorcyclist, Michael LaDue, 59, of Tenino, moved across lanes to the right shoulder, where he collapsed, said Zapalac, who stopped to see if the biker needed help.
LaDue told Zapalac he couldn't hear what he was saying, and when he pulled off his helmet, Zapalac said the hair on the right side of the motorcyclist's head was singed and his ear was black.
"Why am I stopped here?" the motorcyclist asked Zapalac.
LaDue, followed by Zapalac and his wife, was able to get back on his motorcycle and drive to the nearest exit, where they waited for emergency personnel.
A store clerk at the exit said LaDue showed him his helmet, which was cracked on the inside and partially melted, KIRO-TV, Seattle, reported.
"He said he felt really, really hot and he grabbed my hand and he was really, really hot to the touch," said the clerk, Brandi Abrego.
LaDue was taken to a Seattle hospital where he was reported to be in satisfactory condition with non-life threatening injuries.