Violent crime increases during warmer weather, no matter the season, study finds. A study analyzing crime data in Philadelphia for 10 years found that rates of violent crime and disorderly conduct are higher when the weather is warmer and more pleasant, even rising sharply during warmer-than-typical winter days. Source 2g.
I think that when the weather is warmer that more violence occurs as the people who do the violence is more likely to be out in the weather. When it is cold out more people stay inside and thus less people are outside to be attacked.
I know that attacks can occur in all sorts of weather, time and places. Sometimes there is no rhyme or reason why one is attacked so always be aware of your surroundings.
Warmer winter temperatures linked to increased crime. Milder winter weather increased regional crime rates in the United States over the past several decades, according to new research that suggests crime is related to temperature's effect on daily activities. Source 7g.