Date: 01/29/2010; Temperature: 33 degrees; Forecast: snow.
Environment should be a consideration when trying to determine what to wear. For instance, one typically does not wear jeans to a formal dinner or a tuxedo to the ball field (unless the person is involved in something that dictates those particular choices).
Environment is not the only thing to consider when trying to decide what to wear, temperature is also helpful in eliminating choices. One should not wear a puffy jacket to the beach on a warm sunny day, for instance. Not only will that person look strange, but they could suffer from a heat stroke or some other medical malady.
Likewise, flip-flops are not appropriate when the outdoor temperature is 37 degrees and snow is in the forecast. Not only could the wearer suffer from frost bite, but their fashion sensibility will take a serious hit in the eyes of others.