Global Weather
Climate
The earth's tilt, rotation and land/sea distribution affect the global weather patterns we observe. While the weather varies from day-to-day at any particular location, over the years, the same type of weather will reoccur. The reoccurring "average weather" found in any particular place is called climate.
German climatologist and amateur botanist Wladimir Köppen (1846-1940) divided the world's climates into several major categories based upon general temperature profile related to latitude. These categories are as follows:
A - Tropical Climates |
B - Dry Climates |
C - Moist Subtropical Mid-Latitude Climates |
D - Moist Continental Mid-latitude Climates |
E - Polar Climates |
H - Highlands |
The map (below) shows where these major categories occur in the mainland United States.
![The major Köppen zones in the U.S.](images/koppenzones.jpg)
Take it to the MAX! Learn about further sub-divisions of these climate zones.
The classical length of record to determine the climate for any particular place is 30 years, as defined by the World Meteorological Organization (WMO). The quantities most often observed are temperature, precipitation, and wind.
The "normals" are computed once every 10 years which helps to smooth out year-to-year variations. For example, the current 30-year normals were calculated from the actual weather data that occurred during the 30 years of 1971-2000. In 2011, a new set of 30-year normals will be calculated using the data from the period of 1981-2010. So, when you hear what the normal high and low temperature for your location, for example, they come from these 30-year averages.