First, consider the temperature range that you need. If you live in an area with extreme temperatures, you'll want to make sure that the thermometer you choose can handle the high and low extremes. Second, take into account the accuracy of the thermometer. If you need to know exact temperatures for scientific or medical purposes, you'll want to choose a model that is highly accurate. Third, think about the size and portability of the thermometer. If you need to take it with you on trips or hikes, you'll want to choose a compact model that is easy to carry. Finally, consider the price. Outdoor thermometers can range in price from a few dollars to hundreds of dollars.