The climate of Pamplona during the festival of San Fermin varies widely. It tends to be hot and dry, but some years the weather has been rainy and cold, particularly late at night or early in the morning. To plan for your trip to Pamplona, check the forecast for this year.
If you plan to watch the Running of the Bulls®, we recommend bringing a sweater or jacket as it can be chilly in the morning before the Bull Run. Mornings are usually temperate but the afternoons can be hot, especially in the Sun section while watching the Bullfights. Evenings are typically cool so we recommend a light jacket or sweater then as well.