The weather in Mesolongi is benefited by its geographical location. It is built in the entry of Patraikos gulf, and it is surrounded by the outfalls of the Evinos and Acheloos rivers. It is also next to the lagoon, which hosts important species of flora and fauna that are obviously aided by the weather features. In general terms, Mesolongi is part of Etoloakarnania, which is the last district of Sterea Ellada. Although the area of Sterea Ellada, to which Mesolongi belongs, is in general very mountainous, the relief of Mesolongi is mainly flat.
The climate in this area is temperate along the coast and becomes dry when heading to the interior areas. The lack of extreme temperatures causes the environment to keep its picturesque wildlife. The predominating climate is comfortably tempered. The lowest average monthly temperature is about 8°C, while the highest is 27°C. The rainfall is mostly concentrated in the areas close to the lagoons of Mesolongi and Etolikos, the measurements are 186 mm, and there is an average of 106 rainy days every year, while snowfall is rare.