Recall that if you’re flying directly below clouds or a cloud base, you need to make sure that you’re at least 500 feet below the clouds. You can fly directly below clouds, you just need to maintain that distance. If you see clouds, but they are not directly above your UAV, then you do not need to maintain the 500 foot part of the rule.
We like the UAV Forecast app, as it will tell you what the cloud base is (and offer a lot of other helpful wind and forecasting information).
You can also calculate the cloud base using the following formula:
1) Calculate the ‘spread,’ where you’re taking the current temperature and subtracting the dew point.
2) Divide the spread by 4.4 (if temperatures are in °F) or 2.5 (if temperatures are in °C), then multiply by 1000.
This will give you cloud base in feet above ground level.