So, as you might guess, bank thermometers and even the kind of thermometers that are available at the hardware store, while good for a close approximation, do not accurately reflect the air temperature. Certainly there are a few steps that can be made to ensure an accurate reading though, such as: putting the sensor in the shade, getting the thermometer away from your house or buildings and putting it away from black top or any dark sort of ground covering. Keep track of your readings too, as you find the best location at your house. One type of forecasting is simply referred to as "persistence"; with all things being equal, what happened the day before is a good indicator of what will happen today. Use this method with our present weather set-up and I bet with a good location for your thermometer, you'll do pretty well getting the next days highs off of the prior day. Try adding a degree if it feels a little less humid.

Good Luck!