Final answer:
At a temperature of 28 °F and calm wind, the most likely form of precipitation at Tommy's house would be snow, if there is sufficient moisture in the air. Otherwise, frost could also form on exposed surfaces due to the temperature being below the freezing point.
Step-by-step explanation:
The temperature at Tommy's house is 28 °F, which is below the freezing point of water (32 °F). With the wind being calm, the form of precipitation that is most likely to occur would be snow, since any atmospheric moisture would freeze before reaching the ground. However, if there isn't enough moisture in the air, there might not be any precipitation at all. It's important to note that while temperature is a crucial factor in determining the type of precipitation, humidity levels also play a significant role in whether precipitation occurs.
Another possibility is that with the temperature being below the frost point, frost may form instead of snow, particularly on surfaces that are exposed to the sky. Frost forms when the air temperature is at or below freezing and there are water vapor molecules nearby that can directly deposit as ice crystals.