Averages for Lisbon in April What's the weather like in Lisbon in April. Temperature. April sees temperatures climb steadily as the summer season kicks off. The average temperature reaches up to around 19°C (that's about 66°F), and at night only dips as low as 11°C (about 52°F). In April you can expect at least 10 days where the temperature reaches between 21°C and up to 26°C.