Use 'clement' when discussing weather that is pleasantly mild, especially when it's unexpected. The sailors enjoyed a clement day at sea, with calm waters and sunshine.
Pro Tip 2/3
Not Sweltering
'Clement' implies moderate temperature, neither too hot nor too cold. We were grateful for a clement evening that was perfect for the outdoor concert.
Pro Tip 3/3
Unexpected Comfort
The term often suggests a pleasant surprise, when weather is better than anticipated. The clement weather was a welcome change from the week of rain.