Meteorologists refer to June 1 as the start of the summer season but the calendar says it starts June 20. What’s the difference?
Meteorologists break down every season into a 3 month time period based on temperature. Meteorological summer is June, July and August. This breakdown is more precise, consistent and makes it easier to calculate yearly seasonal statistics. This is helpful when comparing weather patterns which is really helpful for those in the agriculture and commerce fields.
The astronomical calendar defines summer, or the summer solstice, as a day when the sun passes directly above 23.5°N latitude or the Tropic of Cancer. It’s the day in the Nothern Hemisphere when we have the longest amount of daylight hours. Since it takes the Earth just over 365 days to travel around the sun, we have a leap year every four years. This causes astronomical season lengths to vary, according to the NWS, between 89 and 93 days. The start dates also vary.
Simply put, meteorological summer is based on the annual temperature cycle and astronomical summer is based on the position of the earth in relation to the sun.