This question already has an answer here:
In the Back to the Future universe, we know what is needed for time travel: a flux capacitor, 1.21 gigawatts and a travel speed of 88 miles per hour (I know there are more requirements than that but I do not want to get bogged down by tiny details).
If any one of these three things is absent, per the story's logic, time travel will not occur.
Here is my problem. Doc was hovering in the DeLorean when it was struck by lightning, sending him back to 1885. How? He was not traveling 88 mph, he was traveling 0mph. Did the filmmakers just overlook this glaringly obvious problem, or is there an in-universe explanation?