A pink sky at sunrise or sunset is a beautiful sight, but an old weather rhyme says it can mean trouble is brewing: “Red sky at night, sailor’s delight. Red sky in morning, sailors take warning.” So does a pink sky really predict rain and stormy weather? Let’s take a closer look at the science behind sky color.
What makes skies turn pink?
The color of the sky is determined by the properties of sunlight and how it interacts with the atmosphere. As sunlight passes through the atmosphere, shorter blue wavelengths are scattered more than longer red wavelengths. This scattering process is called Rayleigh scattering.
In normal conditions, the sky appears blue because blue light is scattered in all directions. But at sunrise or sunset, the sun’s light has to pass through more atmosphere. Much of the blue light has been scattered away, allowing more red light to come through, causing the sky to take on orange and pink hues.
Clouds, dust, pollution, and water droplets in the atmosphere can also affect how light is scattered and absorbed, influencing the colors we see. So in summary, the reddish and pink colors are caused by the long wavelengths of light that remain visible when the short blue wavelengths have been scattered away.
Why does a pink sky signify changes in weather?
There are two key reasons why a pink sky can signal a change in weather:
1. High-level clouds
Pink skies are often caused by high-altitude cirrus clouds composed of ice crystals. These thin and wispy clouds come in the high troposphere, at altitudes over 20,000 feet. Cirrus clouds contain millions of ice crystals, which act to both scatter and reflect sunlight.
As cirrus clouds pass overhead near sunrise or sunset, they scatter the shorter blue wavelengths and allow more red light to shine through, causing pink, orange, and red colors to dominate.
So in summary, the presence of high cirrus clouds helps create the conditions for vivid pink and red skies. These clouds are often the leading edge of an approaching weather system or front that brings increasing clouds and precipitation.
2. Air moisture and temperature changes
Increased water vapor and changing temperatures in the atmosphere can also contribute to vivid sunset colors. As a weather system approaches, increasing moisture and shifting temperatures in the troposphere act to intensify sunset colors.
Water droplets in the troposphere scatter light effectively at the red end of the visible spectrum. Meanwhile, temperature fluctuations alter the balance between scattering and absorption. These atmospheric changes allow more long red wavelengths to reach the observer compared to short blue wavelengths.
So moist, unsettled conditions caused by an approaching weather system are also favorable for vivid sunrises and sunsets. The air contains more water droplets and is undergoing temperature changes that bring out those pinks and reds.
Does a pink sky always mean storms are coming?
In summary, a pink sky is caused by specific atmospheric conditions – namely, moisture, high clouds like cirrus, and changing temperatures. Since these conditions often occur with an approaching weather front or storm system, there is good reason to link pink skies with unsettled weather.
However, it isn’t an exact science. Here are a few important caveats:
– Pink skies can happen anytime, not just ahead of storms. Other atmospheric factors like dust, pollution, or humidity can create vivid colorations on their own.
– The time of day matters. A pink sky in the morning indicates conditions are already changing, meaning rain could arrive soon. But an evening pink sky means fair weather is often still ahead for the next 12-24 hours.
– Location matters. Coastal areas are more likely to see incoming weather from the ocean changes. Inland areas have fewer cues of approaching fronts.
– Time of year matters. In mid-latitudes, approaching fronts are more frequent in spring and fall. So pink skies have higher predictive power during transition seasons versus summer and winter.
– Strength of the front matters. Weak cold fronts may only bring clouds, while strong fronts bring heavy rain. The intensity of pinkness is not always related to the intensity of the storm.
So in conclusion, while pink skies and “red sky at night” rhymes have reasonable scientific merit, they do not always guarantee wet weather is on the way. Use pink skies as one observable factor when forecasting, but consider they are not definitive proof.
Examples of pink skies linked to weather changes
Let’s look at some real examples that illustrate how pink skies can be associated with incoming weather:
March 28, 2017 – London, England
| Date | March 28, 2017 |
| Location | London, England |
| Sky Color | Deep pink and purple tones at sunset |
| Following Weather | Rain and cold front moved in 36-48 hours after pink sky observed |
In this case, the deep pink hues were caused by high cirrus clouds from an approaching weather system. Significant precipitation and a drop in temperatures occurred 1-2 days later across the United Kingdom.
September 8-9, 2020 – San Francisco, California
| Date | September 8-9, 2020 |
| Location | San Francisco, California |
| Sky Color | Deep orange and pink tones lasting for several evenings |
| Following Weather | First rainstorm of wet season moved in 48-72 hours after pink skies first observed |
The prolonged vivid sunsets were caused by wildfire smoke and increasing moisture ahead of the front. Significant rainfall and mountain snow arrived shortly after the multi-day spectacle of color.
January 28, 2019 – Midwest U.S.
| Date | January 28, 2019 |
| Location | Midwest U.S. |
| Sky Color | Bright pink tones at sunrise mixed with blue |
| Following Weather | Major snowstorm and cold blast hit 1-2 days after pink sky reports |
These pink morning skies were seen ahead of a winter storm system that brought blizzard conditions, icy temperatures, and over a foot of snow across several states.
Conclusion
In summary, vivid pink skies are often linked to approaching weather fronts and storms, but they can occur in other conditions too. While pink sky rhymes are useful weather folklore, there are many variables that affect both sky colors and the timing/intensity of storms.
Use pink skies as one observation when forecasting, but consider other clues like humidity, wind shifts, and pressure changes too. And allow a modest delay, as the preceding weather shift may take 24-48 hours to arrive after a pink sky is spotted at sunrise or sunset.
