Clime
← Back to Blog
Guides

Understanding Cloud Cover Forecasts: A Step-by-Step Guide

June 18, 2026 · The Clime Team
Understanding Cloud Cover Forecasts: A Step-by-Step Guide

Cloud cover refers to the fraction of the sky obscured by clouds when observed from a particular location. Understanding cloud cover forecasts is essential for various activities, from photography to aviation. This guide provides a step-by-step approach to interpreting these forecasts.

1. What Is Cloud Cover?

Cloud cover indicates the percentage of the sky covered by clouds. Meteorologists often express it as a percentage or fraction of the total visible sky. For instance, a forecast might state that 70% of the sky is expected to be cloudy. This means that 70% of the sky will be obscured by clouds, and the remaining 30% will be clear.

2. How Is Cloud Cover Measured?

The standard international unit for measuring cloud cover is the okta, which divides the sky into eighths. A trained observer estimates how many of these eighths are filled with cloud of any type or height. The scale runs from 0 to 8:

  • 0 oktas: Completely clear sky
  • 1 okta: One eighth or less of the sky has cloud
  • 3 to 4 oktas: Roughly half the sky is cloudy
  • 7 oktas: Nearly full cloud cover with small breaks

This method provides a standardized way to quantify cloudiness. (biologyinsights.com)

3. What Do Forecast Terms Mean?

Weather forecasts use specific terms to describe sky conditions based on the percentage of the sky covered by opaque clouds:

  • Clear/Sunny: 1/8 or less of the sky covered
  • Mostly Clear/Mostly Sunny: 1/8 to 3/8 covered
  • Partly Cloudy/Partly Sunny: 3/8 to 5/8 covered
  • Mostly Cloudy: 5/8 to 7/8 covered
  • Cloudy: 7/8 to 8/8 covered

These descriptors help convey the expected sky conditions in a concise manner. (weather.gov)

4. How Are Cloud Layers Reported in Aviation?

In aviation, cloud cover is reported using three-letter abbreviations followed by a three-digit height in hundreds of feet above ground level (AGL). The abbreviations describe how much of the sky is covered:

  • FEW: 1/8 to 2/8 of the sky covered
  • SCT (scattered): 3/8 to 4/8
  • BKN (broken): 5/8 to 7/8
  • OVC (overcast): 8/8, completely covered
  • SKC (sky clear): No clouds at any altitude

For example, a code of BKN025 means a broken layer at 2,500 feet AGL. (legalclarity.org)

5. How Does Cloud Cover Affect Weather?

Cloud cover significantly influences weather patterns and daily activities. It affects temperature, precipitation, and visibility. For instance, overcast conditions can lead to cooler temperatures and reduced sunlight, while clear skies typically result in warmer temperatures and more sunlight. Understanding cloud cover forecasts helps in planning activities like photography, outdoor events, and travel.

6. How Can I Access Cloud Cover Forecasts?

Cloud cover forecasts are available through various sources, including:

  • National Weather Service (NWS): Provides detailed forecasts and explanations of sky conditions.
  • Weather Apps and Websites: Offer real-time updates on cloud cover and other weather parameters.
  • Aviation Weather Services: Provide specialized forecasts for aviation, including cloud cover at different altitudes.

By understanding how cloud cover is measured and reported, you can interpret forecasts more effectively and plan your activities accordingly.

Highlights:

Frequently Asked Questions