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In Melissa's case, the upstream temperatures were being specified at a distance of 100 feet. With a ten mile per hour wind, it would take air about seven seconds to travel that distance. And in seven seconds, air doesn't have very much time to warm up from its starting temperature. Even though the ground is heating up all day, the air only has seven seconds to warm up and in seven seconds, air doesn't have very much time to change its temperature.
This made sense to Melissa. It seemed reasonable that to forecast the temperatures at a particular spot on a windy day, anyone, even a computer, would need to know the temperatures some distance from the spot. So Melissa put the edges of the model at a distance of 100 miles from the sixteenth green, and told the model to make temperature forecasts for every twenty miles within the model domain. She also decided to be a bit more careful with the land surface part of the model and specified the type of soil and moisture for each one of these grid points.
With this new forecast, the weather computer was basically taking the air as it came in from 100 miles upstream and allowing it to be heated or cooled as passed over different types of land on the way to the sixteenth green. The computer only knew about five different 20-mile-wide strips of land, so there wasn't much detail there, but it was still a lot more realistic than before. So Melissa's temperature forecasts were a success.
Review: The physical processes that must be simulated by a computer to forecast low-level temperatures are the same ones that affect the low-level temperature (big surprise): radiative heating and cooling of the ground, turbulent mixing of air, temperature advection, and (to a lesser degree) direct loss of radiation from the air. And these all must be simulated for air parcels as they journey across the land and sea. The accuracy of the forecast may suffer if these processes aren't computed correctly, or if there aren't enough grid points to accurately simulate horizontal advection, vertical mixing, or changes in land characteristics.
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