rainforecast

Forecast desk · Interactive

Cloud base rule of thumb

Estimate a lifting condensation level from temperature and dew point spread.

How this works

Enter the values shown, review the result, and verify assumptions before acting. The calculation is performed on your device without uploading these entries.

Estimate a lifting condensation level from temperature and dew point spread. The input fields are labeled with the units or formats used in the calculation. Change one value at a time to see how the result responds, and compare the output with the worked example below.

Formula or method

LCL approx. = (T−Td) × 125 metres

The method above describes the calculation or algorithm being used by this browser utility. It is shown so you can understand the result, check assumptions and repeat the calculation independently if needed.

Worked example

A 4°C temperature/dew-point spread suggests roughly 500 m above ground.

Limitations and accuracy

Highly simplified; not an aviation forecast.

The calculation runs locally in your browser. No result is guaranteed to be suitable for financial, legal, medical, or safety-critical decisions. Check independent authoritative sources in those cases.

More context

A forecast describes expected conditions under uncertainty, not a guaranteed outcome. Chance of precipitation refers to probability at a location and must not be confused with the percentage of a day it rains. Heat index and wind chill describe apparent conditions only in their valid temperature and humidity ranges. For severe weather, follow official alerts and local authorities. Forecast coverage depends on the data provider; this site does not promise worldwide live forecasts.