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Estimating Cloud Bases

Source: www.pilotworkshop.com/tips/estimating-cloud-bases, Featuring Scott Dennstaedt

Subscriber Question:

"Are there any good rules of thumb to estimate the height of the cloud bases?"
- Larry J.

Scott:

"Many pilots that know me are well aware that I am not a fan of rules of thumb with respect to weather. Largely this is because they don't work in many circumstances. However, one of the rules of thumb that tends to work pretty well for estimating the base of the lowest cloud deck is derived from the temperature and dewpoint temperature at the surface.

Here's what you do. First, find the dewpoint depression in degrees Fahrenheit – that's the temperature-dewpoint spread. Next, double it. Finally, add two zeros to the result.

For example, assume the temperature at the surface is 59°F and the dewpoint is 57°F. The dewpoint depression (temperature - dewpoint) is 2 degrees. Doubling this leads to a 4 and adding two zeros results in an estimate for the cloud bases of 400 feet AGL.

This rule of thumb works pretty well for cumuliform and stratiform clouds as long as it isn't raining or snowing. Snow and especially rain tends to raise the dewpoint temperature quite a bit which will provide an artificially lower cloud base when using this rule of thumb."