Why does seasons/weather affect people’s behavior and state of mind?
Various weather conditions can affect people's mood. A person's negative mood can be affected by higher temperatures, and the positive mood can be affected by more sun and less wind [1]. Higher temperatures are also linked to greater amounts of aggression [2]. On the other hand, extreme winter cold and extreme summer heat have a similar effect on people by making them stay indoors more and get less exercise [4]. Cold and hot weather also frustrates people because they have to spend time putting on extra winter or summer gear when they go outdoors [4]. Humid conditions are also uncomfortable and demotivating [4]. This means that when weather conditions are favorable, people tend to spend more time outdoors, which can bring about a positive change in mood [3].
Weather most certainly has an impact on people's mood, whether it's being trapped inside during the winter or being outside enjoying the nice weather. [1][2][3][4]  One study in 2005 found that pleasant weather (higher temperature or barometric pressure) was related to higher mood, better memory, and "broadened" cognitive style as people spent more time outside. [3]  In contrast, extreme heat (above 70 degrees Fahrenheit) decreased reports of positive emotions and increased reports of negative ones, when compared to average daily temperatures of 50 to 60 degrees Fahrenheit. [2]  Being trapped inside during the winter, or not having the freedom to enjoy the nice weather, can affect mood and even mental health. [4]  One study conducted in Australia found that increases in humidity were associated with "high or very high distress," and another study found that heat is even impacting sleep. [2]  Overall, weather most certainly has an impact on people's mood, whether it's being trapped inside during the winter or being outside enjoying the nice weather. [1][2][3][4]