What Were Those Horizontal Rainbow Stripes Stretching Across the Sky on Wednesday?

By Chris Martz | June 12, 2019

Numerous people (including myself) have come forth to share some photos of colorful rainbow stripes spotted within the clouds over the Washington, D.C. area on Wednesday. A handful of photos of these strange, yet mesmerizing optical phenomena have been shared on Twitter from people in various locations throughout the area, including Frederick, MD, Loudoun County, VA, and Berryville, VA.

While many refer to this optic as a “fire rainbow” due to it’s colorful, flame-like appearance, the technical term for this is a “circumhorizontal arc.”¹ ² ³ Often spotted during the spring and summer months, circumhorizontal arcs arise when sunlight is refracted (bent) through hexagonally-shaped ice crystals while the sun is simultaneously at 58° above the horizon (usually between noon and 2:00 p.m.).¹ ² ³ ⁴ When the sun’s rays strike ice crystals composing high, thin, wispy cirrus clouds (which form at elevations greater than 20,000 feet),⁴ the rays are split into a wide array of colors.¹ ² ³ ⁴ Unlike regular rainbows, these clouds have nothing to due with rain.² ³

Circumhorizontal arcs are not to be confused with circumzenithal arcs, which are upside-down rainbows that occur when the sun is anywhere from 5° to 32° above the horizon.¹ ³

REFERENCES

[1] Lam, Linda. “Fire Rainbow Appears in Kentucky Sky.” The Weather Channel. May 8, 2018. Accessed June 12, 2019. https://weather.com/science/weather-explainers/news/2018-05-08-fire-rainbow-circumhorizontal-arc-kentucky.

[2] Samenow, Jason. “Colors ‘purer’ than those of the rainbow’ painted skies near Washington Wednesday. Here’s and explanation.” The Washington Post. June 12, 2019. Accessed June 12, 2019. https://www.washingtonpost.com/weather/2019/06/12/colors-purer-than-those-rainbow-painted-skies-near-washington-wednesday-heres-an-explanation/?utm_term=.390ed2306f4c.

[3] Erdman, Jonathan. “The Science Behind the Odd Rainbow Stripes Everyone Saw in Western Wisconsin.” The Weather Channel. June 8, 2015. Accessed June 12, 2019. https://weather.com/science/weather-explainers/news/circumhorizontal-arcs-wisconsin.

[4] Williams, Ashley. “Beachgoer captures rare, colorful phenomenon decorating the afternoon sky.” AccuWeather. May 27, 2019. Accessed June 12, 2019. https://www.accuweather.com/en/weather-news/beachgoer-captures-rare-colorful-phenomenon-decorating-the-afternoon-sky/70008372.

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