What’s this rainbow patch in the sky?
What did Jeffrey see? According to Les Cowley’s one-of-a-kind website Atmospheric Optics, a rainbow patch like this one, seen under a cloud, is most likely just a portion of an ordinary rainbow. Les provided another example of a similar patch of rainbow below a cloud in Arizona, and he explained it this way:
Why an odd colored patch?
The sun was ~30 degees high and the antisolar point [point opposite the sun in the sky] was to the right of the image. If there had been rain nearby, a whole rainbow would have been seen roughly along the colored lines. Instead, the rain shower was far away and falling in slanting streaks. Where the rain was at the correct angle to the sun (i.e on the rainbow cone) it lit up in rainbow colors. The patch has a vertical appearance because the eye is guided by the near vertical rain streaks.
Rainbow patch links
To read more about patches of rainbow and see another example, visit this page at Atmospheric Optics.
Share your own photos at EarthSky Community Photos.
Bottom line: The rainbow patch appearing beneath a cloud in Oak Harbor, Washington, is a portion of a rainbow illuminating the far-off raindrops beneath the cloud.