The link between aggression and hot weather is long-noted but it is still not proven why heat has this effect and how great the problem is. July and August in the USA are on average both the hottest months and the most criminally violent. Explanations range from increased irritability with summer heat to the combination of increased drinking, people gathering outdoors in public places and spending more time with families. Some research suggests regional differences: in Dallas, US, where high temperatures are the norm in summer, behavioural changes were most marked during a combination of heat and extreme weather conditions such as storminess. It is argued that such conditions make people uncomfortable and disrupt them psychologically.