When you start in May, the weather in southern France is usually nice. There might be some sun and rain, and maybe some heavy rain sometimes. The temperature during the day is around 19-20°C, and it gets cooler in the evening, down to about 12-13°C. Rain isn't usually too heavy, between 0.5mm and 5.0mm per day, but it might be more in some places.
As you keep walking and get to Toulouse, the weather stays more or less the same, with some sun, cloud and possible rain. Daytime temperatures stay in the low twenties and it cools down to the lower teens at night – comfortable temperatures for the journey.
As you head towards Oloron-Sainte-Marie, the weather might change. It could be sunny or there might be heavy rain, but the temperatures usually stay the same.
As you start going uphill towards Somport, the weather can change a lot. You might get a lot more rain, with some days getting more than 5mm, and the temperatures can get cooler, down to around 17-18°C during the day and 8°C at night.
So, you should be prepared for sunny, cloudy and rainy weather. The temperatures are usually nice for walking — not too hot, and the nights aren't too cold. This variety is what makes the Arles Way such a good and interesting path to walk on. Despite some rain, there are lots of sunny days that make for a great walk through southern France's beautiful natural and cultural sights.
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