Lightning struck the clock tower at precisely 10:04 p.m. Sending the necessary 1.21 gigawatts into the time vehicle, which vanished in a brilliant flash of light leaving a pair of fire trails behind.

10 seconds sound clip from the Back to the Future Part III movie soundboard.

You can hear this line at 00:05:35.945 in the DVD version of the movie.

Quote context

[...]

(THUNDER RUMBLING)

- Hey, kids, what time is it?

- Howdy Doody time!

- Great Scott!

- Howdy Doody time?

- Date. Sunday, November 13, 1955.7:01 a.m.

- Last night's time travel experiment was apparently a complete success.

- Lightning struck the clock tower at precisely 10:04 p.m. Sending the necessary 1.21 gigawatts into the time vehicle, which vanished in a brilliant flash of light leaving a pair of fire trails behind.

- I, therefore, assume that Marty and the time vehicle were transported forward through time into the year 1985.

- After that... After that, I can't recall what happened. In fact, I don't even remember how I got home.

- Perhaps the gigawatt discharge coupled with the temporal displacement field generated by the time vehicle caused a disruption of my own brain waves resulting in a condition of momentary amnesia.

- Indeed, I now recall that moments after the time vehicle disappeared into the future...

[...]