Wet weather. The local council where I live is very protective of its fields and calls them out prematurely in some instances. The council actual has three ground statuses, open, closed and light activities only i.e. dog walking. Football can only be played once the fields are open. If there is a large down poor early in the year then the grounds tend to hold quite a bit of that water throughout the season meaning that even when it only mildly rains the grounds may still be impacted enough to call them out. As a result, sometimes games are called off due to the grounds not being available.
This is where the artificial fields once again have an advantage as they can be played on even in rainy conditions. This means that not only games can continue as scheduled but teams can also train when they are supposed to as well. The ground does become quite slick, and the ball tends to skid however if constructed correctly then the water would not pool on the surface unless there was an extreme downpour of rain.
In hot weather at the start of the season natural grass is quite pleasant to play on. The ground absorbs most of the heat meaning that the temperature often remains the same whether you are on the pitch or not. Towards the end of the season hot weather is not really a factor as it is winter, and the temperature rarely gets above 20 degrees. However, when it does, the ground can sometimes reflect a bit of the heat meaning that it can be a little bit hotter on the pitch than elsewhere but still reasonable.
Artificial pitches in hot conditions become like a frying pan. The black rubber attracts the heat and the plastic grass does not help. You can regularly see heatwaves coming off the pitches when they are exposed to full sunlight. Even in modest conditions the heat is still significantly higher during the day than the surrounding area. In hotter conditions provided it is at the start of the season the Natural grass pitches are significantly more comfortable to play on.