A red sky at night or in the morning is a phenomenon caused by the scattering of sunlight through the atmosphere. This scattering effect can indicate different weather conditions based on the time of day it occurs. A common phrase uses a red sky at night or in the morning as an indication that a storm may be coming soon. But does a red sky always mean a storm is on the way? Let’s take a closer look at the science behind red skies and what they can tell us about upcoming weather.
What Causes a Red Sky?
The red color in skies is caused by the scattering of sunlight through dust particles and water droplets in the atmosphere. Shorter wavelength blue and violet light is more easily scattered, allowing more of the longer wavelength red light to pass through. The red light refracts as the sun’s rays pass through these particles near the horizon at sunrise or sunset. This causes the remaining sunlight passing through the atmosphere to appear more red.
Here are some of the main factors that can contribute to red skies:
– Dust – Dust particles in the atmosphere, from sources like desert sand or pollution, scatter blue light the most. This leaves more red light to give the sky a red hue.
– Water droplets – Moisture in the air in the form of water droplets or humidity provides surfaces for light to refract off of. Droplets from high clouds or moisture near the horizon scatter light and can lead to red skies.
– Particulate matter – Other fine particulate matter like smoke, pollution, ash, or smog act similarly to dust and water droplets by scattering light. More particles lead to more vibrant red colors.
– Cloud cover – The types and heights of clouds present when the sun is low on the horizon also play a role in the scattering of light. High cirrus clouds and low lying clouds near the horizon accentuate the effect.
Morning vs Evening Red Skies
The time of day that a red sky occurs can make a difference in what it signifies about upcoming weather. This is tied to the positioning of weather systems relative to the observer. Here is an overview of how morning and evening red skies can differ:
Morning Red Skies
– Caused by clouds and moisture to the east of the observer as the sun rises behind them.
– Signify that wet weather is likely approaching from the west later in the day.
– Suggest that a low pressure system and/or related cold front is moving in from the west.
– Point to precipitation and possibly stormy weather within 12 to 24 hours.
Evening Red Skies
– Caused by clouds and moisture to the west of the observer as the sun sets behind them.
– Signify that wet weather has passed or is moving away to the east.
– Suggest that clearing conditions are on the way from the west overnight.
– Point to improving weather and drier conditions within 12 to 24 hours.
So in general, a morning red sky means stormy weather is likely coming, while an evening red sky means storms have passed or are moving away.
Common Red Sky Sayings
There are several common folklore sayings that mention red skies in relation to the weather:
– “Red sky at night, sailor’s delight. Red sky in the morning, sailors take warning.” This is the most well known red sky rhyme. As discussed above, it captures the general association between morning red skies meaning storms are coming and evening red skies meaning good weather is on the way.
– “Evening red and morning gray, sends the traveler on his way. Evening gray and morning red brings down rain upon his head.” A variation of the same principle, using gray skies instead of only referencing red.
– “When the sun sets bright and clear, an easterly wind you need not fear. When the sun sets in a cloudy sky, tomorrow rain will pass nearby.” Relates clear evening sunsets with dry conditions from the west and cloudy sunsets with wet weather.
– “If red the sun begins his race, expect that rain will flow apace.” Again connects morning red sunrises with approaching storms.
These sayings capture centuries of observational wisdom about the patterns between red skies, cloud cover, and changing weather. While not 100% accurate all the time, they provide useful rules of thumb.
The Science Behind Red Sky Weather Sayings
The common red sky sayings have scientific merit in terms of atmospheric optics and meteorology. Here is how the science supports the sayings:
– Morning red skies do often indicate an approaching low pressure area and associated cold front from the west, which brings precipitation.
– Evening red skies can signify a high pressure area and clearing conditions moving in from the west, resulting in drier weather.
– The position of the sun relative to moisture and cloud layers creates the red scattering effect and points to changing weather patterns.
– Increased dust particles, water droplets, and moisture content in the air frequently accompanies storm systems and amplifies the red sky effect.
– Cloud patterns like high cirrus clouds in front of and low cumulus clouds behind frontal boundaries produce red sunrises/sunsets.
While the sayings are not absolutely true in all cases, they describe common correlations between red skies and shifting weather due to the movement of pressure systems and moisture. The optics of sunrises/sunsets filtered through the atmosphere provides clues about what is happening meteorologically.
Limitations of Red Sky Weather Predictions
Despite the useful general associations described in the red sky sayings, there are also limitations in using morning or evening red skies alone to predict upcoming weather:
– Location matters – The sayings depend on the observer’s location relative to the position and movement of weather systems, which isn’t always consistent.
– Timing varies – The precise timing of when wet or dry conditions will arrive after a red sky can fluctuate.
– Oversimplification – Not all red skies have a clear association with a certain type of weather change. Other weather factors are at play.
– Daytime red skies – Red hues during middle of the day due to wildfire smoke, dust storms, or pollution may not have predictive meaning.
– Visibility conditions – Poor visibility from fog or obstructions on the horizon can hide red sunrises/sunsets.
While red skies can provide helpful clues about changing weather patterns, they should be considered in combination with other observations, forecasts, and meteorological data when predicting storms.
Other Weather Signs of Approaching Storms
Beyond just red skies, there are other weather signs that can signify storms are likely on the way:
– Increasing wind speeds and shifts in wind direction
– Sudden drops in barometric pressure
– Cooler temperatures and increasing humidity
– Swelling seas and rising surf conditions
– Low clouds moving in overhead and thickening atmospheres
– Distinct cloud patterns like shelf clouds and roll clouds
– Formation of cumulonimbus rain clouds and thunderstorms
– Changes in animal behaviors becoming more erratic or anxious
Observing multiple indicators like these in addition to a red sky at morning can give even stronger evidence that wet and stormy weather is imminent.
Conclusion
In summary, red sky sayings based on the appearance of morning or evening red skies do have scientific validity, but aren’t 100% foolproof as weather predictors. A red sky at night or in the morning caused by the scattering of sunlight through the atmosphere can signify changing weather patterns, especially when low pressure systems and frontal boundaries are approaching or clearing out. However, red skies alone don’t guarantee certain expected weather will arrive on schedule. Paying attention to other meteorological signs in addition to red skies provides the best clues about when stormy weather may be on the way. While not a perfect forecasting technique, observing the skies for changes in color and cloud patterns remains a useful weather wisdom tool.
