To isolate the problem, the first thing to check is if the weather algorithm is outputting reasonable numbers. To do so, open a browser and type in the following command:
substitute the first xxxxx with your location (such as zip code), and second xxxxx with your Wunderground API key. The output should contain a number called scale=xxx and that’s the percentage it calculated.
The weather algorithm is explained here:
In your particular case, it could very well be that the weather condition happened to result in 100% (humidity is slightly above 30%, and temperature is slightly above 70F).