Meteorologists generally define four seasons in many climatic areas: spring, summer, autumn (or fall) and winter. These are demarcated by the values of their average temperatures on a monthly basis, with each season lasting three months. The three warmest months are by definition summer, the three coldest months are winter, and the intervening gaps are spring and autumn. Spring, when defined in this manner, can start on different dates in different regions. In terms of complete months, in most
North Temperate Zone locations,
spring months are March, April and May, although differences exist from country
to country. (Summer is June, July, August; autumn is September, October,
November; winter is December, January, February). The vast majority of South Temperate Zone locations
will have opposing seasons with spring in September, October and November.
Swedish meteorologists define the beginning of spring as the first occasion on
which the average daytime temperature exceeds zero degrees Celsius for seven
consecutive days, thus the date varies with latitude and elevation.