What is Persistence?
Persistence is just taking today's weather and forecasting that tomorrow's weather will be exactly the same. This is considered an unskilled forecast because it doesn't take any special training to make. You can forecast the weather yourself this way! Just take today's high temperature, low temperature, and precipitation and say that tomorrow, and the next day, and the next, will be exactly the same.
If you see that the Persistence forecast has a higher accuracy percentage than the skilled forecasts, then you will know that they are not doing their job! The Persistence forecast should always be less accurate than the weather professionals.