Other facts from our historical weather data: Which months have the greatest rainfall in Porthmadog? Most rainfall (rainy season) is seen in October, November and December. Which is the warmest month in Porthmadog? July has an average maximum temperature of 19°C (66°F) and is the warmest month of the year. Which is the coldest month in Porthmadog? The coldest month is February with an average maximum temperature of 8°C (46°F). Which is the wettest month in Porthmadog? December tops the wettest month list with 171mm (6.7 in) of rainfall. Which is the driest month in Porthmadog? May is the driest month with 95mm (3.7 in) of precipitation. Which is the sunniest month in Porthmadog? May is the sunniest month with an average of 169 hours of sunshine. No idea where to travel to this year? We have a tool that recommends destinations based on your ideal conditions. Find out where to go with our weather planner.