The best time to visit Runcorn for pleasant weather and outdoor activities is generally from late spring to early autumn, specifically May through September.During these months, you'll experience the warmest temperatures and the most sunshine, making it ideal for exploring local parks, walking along the Mersey, or visiting nearby attractions. July and August are typically the warmest, with average temperatures around 20°C (68°F), great for enjoying events like the Runcorn Carnival or a leisurely boat trip on the Manchester Ship Canal.For those who prefer slightly cooler weather and fewer crowds, May, June, and September offer a comfortable balance. The days are still long, and the weather is generally mild enough for outdoor excursions without the peak summer heat. These months are also good for visiting historic sites like Halton Castle, as the grounds are usually well-maintained and accessible.If you're interested in indoor activities or don't mind cooler, potentially wetter weather, the off-peak months can offer good value on accommodation.