HELENA — Although temperatures have been warmer over the last few days, climatologically, the Northern Hemisphere is just now entering the coldest time of year.
A person might think we would experience our coldest temperatures of the year once we reach our maximum tilt away from the sun on the winter solstice around Dec. 20 or Dec. 21, and similarly, we would experience our hottest temperatures once we reach the maximum tilt toward the sun on the summer solstice. On these dates, we're receiving the least and most insolation from the sun.
Water absorbs a large amount of energy before it actually changes temperature because of what's called specific heat. The ocean waters and the water vapor in our atmosphere take time to bottom out or reach the maximum, and this phenomenon is called seasonal lag.
Think of seasonal lag like the opening and closing of a freezer door. When you open the icebox, it takes some time to feel the full effect of the colder air spilling out. The winter solstice represents the point at which the freezer door is fully open. At this point, the earth is tilted as far away from the sun as you can get. As you close the door, this represents the earth slowly tilting toward the sun.
There's still plenty of winter left, and plenty of cold air still just out of the freezer. That's the point where we are at night now. The freezer door is closing but the air is its coldest. The good news is it's only up from here.