Outside temperatures are often the cause of higher bills. Heating and cooling your home is often the majority of your total energy use. So, it makes sense that during periods of extreme heat or cold, the additional load will cause an increase in electric use.
In the winter, your heating system will run more often and will increase your electric use. Also, the addition of space heaters, electric fireplaces or livestock heaters can dramatically increase your energy consumption.
In the summer, your AC runs more often and will increase your electric use. Also, running dehumidifiers, pool pumps, or that refrigerator in the garage during summer months, will also add to your electric bill.