The best time to go to Petrosani is during the late spring (May to June) and early autumn (September to October) when the weather is pleasant for outdoor activities.
During these months, you'll find comfortable temperatures for exploring the surrounding Jiului Valley National Park and its hiking trails. The spring brings blooming wildflowers, while autumn offers colourful foliage, making for picturesque scenery. This period avoids the intense heat of summer and the colder, sometimes snowy, conditions of winter, which can make mountain access more challenging.
For travellers interested in hiking and outdoor pursuits, these shoulder seasons are ideal. The trails are generally clear, and the natural beauty of the Retezat Mountains and Parâng Mountains is at its peak. It's also typically less crowded than the peak summer months, allowing for a more tranquil experience.
If you're interested in winter sports, then December to March would be the best time to visit, particularly for skiing and snowboarding in the nearby Parâng Mountains.