I have one of those multifunction digital clock alarms that also
displays the temperature and humidity. In addition it also has a
weather display which can show a shining sun (during daylight hours
anyway), and a number of differently sized clouds depending how bad the
weather is supposed to be. In my estimation the weather interpretation
isn't too far from reality.

While I can appreciate how the temperature and humidity are measured I
wonder how it can come up with an evaluation of the current weather
conditions.

Any ideas?