San Luis Potosí sits at 1,877 metres elevation, which keeps temperatures moderate year-round. Summers (May–September) are warm but rarely oppressive — expect highs around 25–28°C and afternoon thunderstorms from June onward. Winters are mild by day (18–22°C) but can get cool at night, particularly January and February.
The best months to visit are October through December and February through April: clear skies, comfortable temperatures, and smaller crowds than the summer high season. Semana Santa (Holy Week before Easter) is a major festival in the region and worth timing a visit around, though the city gets busier. The Feria Nacional Potosina runs through August and is the main annual fair, drawing regional food and craft vendors alongside livestock shows and music.
If your trip combines the city with the Huasteca Potosina (the lush lowland region to the east with waterfalls and rivers), plan that portion for the dry season, October through March, when the waterfalls run full and the heat is manageable.