HOT, DRY AIR MOVES IN FROM THE SAHARA. IT IS COOLER BY A FEW DEGREES CELSIUS BECAUSE THERE IS NO MOISTURE TO TRAP THE SUN'S RADIANT ENERGY, AND MOST OF THE HEAT ESCAPES INTO SPACE AGAIN.
The growing season is when there is no frost and plants can grow (which lasts from 100 to 175 days).
Plants usually start growing when the daily temperature reached about 50° F. In temperate grasslands the average rainfall per year ranges from 10-30 inches. In tropical and sub-tropical grasslands the average rainfall per year ranges from 25-60 inches per year The amount of rainfall is very important in determining which areas are grasslands because it's hard for trees to compete with grasses in places where the uppers layers of soil are moist during part of the year but where deeper layer of soil are always dry.