As warm air rises, it becomes colder. Gradually, the water vapor in the air turns into very small drops of water. The molecules in the water grab hold of tiny bits of dust, pollen, and other types of pollution. The water molecules condense onto these particles and collect together. All those molecules together make a cloud. When clouds become heavy, they release water back to the earth as rain, sleet, snow, or hail.
Snow begins its life as an ice crystal. Ice crystals form when a cloud’s temperature is below freezing (32 ˚ F/ 0 ˚ C). If the air temperature below the cloud is also below freezing, the crystals cling together and fall to the ground like snowflakes, thanks to gravity.
The same amount of sunlight hits the Earth all over. However, the sun’s rays fall more directly on the equator- the bulging center of the Earth’s sphere – than at its poles. As a result, equatorial Africa and South America are much warmer than the Arctic or Antarctica.
Lower air pressure causes lower temperatures. Hiking up a mountain is cool, and as you climb, it gets even cooler! The temperature of the air is determined in part by the pressure it is under. As you rise up further from sea level, the air pressure gets lower and lower… and so does the air temperature.
Just as a thermometer measures temperature, a barometer measures air pressure. When the barometer shows high pressure, that means the weather is generally clear. When the barometer goes down, the chances for a storm go up!