The official start of summer is just around the corner. In fact, it's actually this weekend, June 20th. The official Summer Solstice occurs at 11:31pm on Sunday night, making June 21st the first full day of Summer. The day of the summer solstice is also the longest day of the entire year, with Louisville seeing close to 15 total hours of daylight with the sun rising at 6:20am and the sunset occurring at 9:10pm.
That being said you may think that the longest day with the most sunshine should be the warmest day of the year as well since after all it is the first day of Summer right? Well, not exactly.
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 sometimes. Or, think about mountaintops in June too. 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.
The beach and sea. Image via Shutterstock/Ozerov Alexander
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.
Via EarthSky.org
