The cloud base can be found by calculating the difference between the surface temperature and the dew point, then using this value to determine the cloud's altitude.
Calculating Cloud Base Altitude
The method uses the concept that air cools as it rises, and when it cools enough to reach its dew point, water vapor condenses into clouds. To find the cloud base altitude, follow these steps:
- Determine the Surface Temperature: Measure the air temperature at the ground level.
- Determine the Dew Point: Measure the dew point at the ground level. The dew point is the temperature to which air must be cooled to reach saturation (100% relative humidity).
- Calculate the Spread: Find the difference between the surface temperature and the dew point. This difference is called the "spread".
- Divide by the Appropriate Constant:
- If your temperatures are in degrees Fahrenheit (°F), divide the spread by 4.4.
- If your temperatures are in degrees Celsius (°C), divide the spread by 2.5.
- Multiply by 1000: Multiply the result from step 4 by 1000. This will give you the altitude of the cloud base in feet above ground level.
Formula Summary
Here is a simplified view of the formula:
| Temperature Unit | Formula |
|---|---|
| °F | Cloud Base (feet) = ((Surface Temperature - Dew Point) / 4.4) * 1000 |
| °C | Cloud Base (feet) = ((Surface Temperature - Dew Point) / 2.5) * 1000 |
Example:
Let's illustrate with an example using Fahrenheit:
- Surface Temperature: 77°F
- Dew Point: 55°F
- Spread: 77°F - 55°F = 22°F
- Divide by 4.4: 22 / 4.4 = 5
- Multiply by 1000: 5 * 1000 = 5000 feet
- Therefore, the cloud base would be approximately 5000 feet above ground level.
Here is another example using Celsius:
- Surface Temperature: 25°C
- Dew Point: 15°C
- Spread: 25°C - 15°C = 10°C
- Divide by 2.5: 10 / 2.5 = 4
- Multiply by 1000: 4 * 1000 = 4000 feet
- Therefore, the cloud base would be approximately 4000 feet above ground level.
Important Considerations:
- This method provides an approximation.
- It assumes a consistent temperature and dew point lapse rate with altitude.
- Local atmospheric conditions can affect the accuracy.
- The resulting altitude is in feet above the location where the measurements were taken.
By following these steps, you can get a solid approximation of the altitude of the cloud base, as described in the reference.
