MINNEAPOLIS (KMSP) - While total daylight hours start to fade (now that our 9pm sunsets are gone), we think temperatures can only get cooler from here. On the contrary, despite the loss of daylight over the next couple of weeks, we are heading into what is typically the warmest days of the year. While there are many factors that can drive when the warmest temperatures of the year occur, it is often 3 to 4 weeks after the summer solstice (longest day of the year).
On Earth, there is always a delay for peaks across the world. Peak ocean temperatures always occur in September and March, several weeks behind peak warm and cold seasons, daily highs and lows are usually after peak sun angle or after the sun actually rises. It’s just the way things work. So, because the sun is typically the driving force for the heat around here, it happens this time of year.
The map above shows the “typical” warmest day of the year. For southern Minnesota its basically now through the 15th. But for the north, it’s a little later when more heat from the Gulf of Mexico and the southern US can make its trip further north. You head to the Moorhead area and it’s usually the first week of August. So what’s up with parts of the south? Why don’t they get their hottest days until August?
That has more to do with dry air. In August, they can get some very dry air to lift northeast from Mexico. The dryer the air, the fast and more efficiently it can heat, and therefore the warmer your temperatures can be. It is very common for this to happen a few days in August in the South. For the Desert Southwest, it’s the same type of situation, but it happens at a different time of year. Far less moisture can be found earlier in the summer, June mostly because Monsoon Season begins sometime in July which adds moisture to the atmosphere and allows temperatures to drop a little. This gives Arizona, New Mexico, and west Texas their “typical” warmest days in June.
For those living right along the Pacific Ocean, it’s the opposite. It can be late August or even early September when those area see their warmest day. This is for two reasons; because water temperatures are warmest at that time of year AND off shore winds are far more prevalent. This can affectively push the cooling sea breeze away from land and allow temperatures right along the coast to soar, creating the warmest day of the year. Pretty cool right?!?