The longest day of the year comes at the summer solstice, but the hottest weather always follows a month or two later. With the past decade the warmest on record, the hot weather nowadays can be very hot indeed – as we in Texas can testify.
The phenomenon of the hot weather following the summer solstice by a month or two is called the lag of the seasons. Why does it happen?
You know it's hot when ... Image Credit: Flickr user Katerha
You can understand it if you’ve ever visited a beach in June. On northern hemisphere beaches in June, 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 after the cold of winter.
Image Credit: jurvetson
Mmm. Beach …
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.
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Because in june the ocean water is still cold and there is still snow on the high mountains. So it takes a couple of months for everything to warm up annd melt all the snow.So thats why it takes a month or two for the hottest weather.
It is easy to explain the “lag of seasons” when you look at the “daily heat budget”. Lets assume you live in an area where you get 16 hours of daylight, and 8 hours of night on the longest day of the year. This results in 8 more hours of daylight. During the dark of night you are loosing heat to space, and during midday you are adding heat from the sun. The hour before and after sunrise and sunset are fairly neutral in adding or loosing heat. As a result there is about 6 hours of extra heating on the longest day. Additional daily heating continues for most of the remainder of summer, even though the amount of daylight gets shorter each day. A month after the longest day, you might still be getting 2-3 extra hours of heating per day. If you add more heat each day, the temperature will rise. This explains why the hottest days of summer are usually about 6-7 weeks after the longest day. The neutral heat gain/loss an hour before and after sunrise and sunset help explain why the hottest day isn’t the last day of summer. A reversal of the “daily heat budget” results in the coldest days of winter occurring 6-7 weeks after the shortest day.
Wow, that was way more complicated than the article. Nice job, doughnut.