The 2019 June solstice has come and gone. But, for us in the Northern Hemisphere, the hottest weather of the year is still to come. The phenomenon of the hottest weather following the summer solstice by a month or two is called the lag of the seasons.
You can understand it if you’ve ever visited a beach in June. On Northern Hemisphere beaches around now, you’ll notice how cold the ocean feels. Or think about mountaintops in June. Ice and snow still blanket the ground on some high mountains. The sun has to melt the ice – and warm the oceans – before we feel the most sweltering summer heat.
That’s why the hot weather lags behind the year’s longest day and highest sun.
By August, ocean water on that same beach will be much warmer. And the snow line will have crept up the mountaintops. That’s why the hottest weather comes some months after the year’s longest day. The land and oceans simply need those extra months to warm up – a scientist might say to store heat – after the cold of winter.
In the Southern Hemisphere now, the same phenomenon is occurring, but, there, the lag of seasons is delaying the year’s coldest weather. The June solstice, for the Southern Hemisphere, is the winter solstice. The coldest weather comes in July and August because the land and oceans in that part of the world take some extra weeks to give up their stored heat.
Bottom line: The solstice marks the height of the sun, but the hottest weather comes a month or two later. That’s because the land and oceans have to warm up, too, before the truly hot summer heat can begin. This phenomenon is called the lag of the seasons.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.