Warm days, cool nights: Dry air means big temperature swings
I doubt anyone is complaining about this “relatively” dry air mass overhead. No? As we know all too well in Northeast Kansas, this time of year can harbor some real beastly humidity levels. Have you ever noticed when its really humid out, the “actual” temperature doesn’t rise too quickly on your thermometer? I know it doesn’t “feel” like that though.
Think of how long it takes to boil a pot of water. It takes a lot of energy to heat water molecules. The same applies in the air: water vapor droplets need a lot of heat from the sun to warm up. Once excited, those water droplets also take a long time to cool down. This is why highs may cap off in the 90s when the humidity is really, really high (versus bumping up into the 100’s with no problem); and, all that water in the air will take a long time to cool off at night (which is why we often don’t fall too far below 80°F when it's disgustingly humid). Dry air is different.
Dry air warms up and cools down very quickly. Take Wednesday morning for example: lows were very chilly in the 50s, but warmed up to near 90 degrees in some cases by Wednesday afternoon. The hot Kansas sun will warm up that cool air in a hurry. At night, in the absence of clouds and wind, those temperatures may mean you'll wind up with an extra blanket on the bed before daybreak.
Another great example of the fast-changing temperatures in a dry air mass can be found in a desert region. It is not uncommon to wake up in the desert with temperatures in the 50s, but end up the day in the 100s. Now, don’t get me wrong, any way you slice it or dice it, a high of 110 degrees or more is just plain brutal. Still, the fact that a temperature can swing 40 to 50 degrees in dry air is just impressive.
Sometimes we do warm up quickly despite high humidity levels. A south or southwest wind might do the trick. Those winds are often from a more dry — and hot — origin. Those breezes will help to draw 100 degree temperatures up from the southwest, sometimes higher. The arrival of that hot air, in conjunction with oppressive humidity already in place, can make for those terribly high index values pushing 110 to 120 degrees. Another way of getting around humidity in the air in order to warm up is through “mixing”. If dry air higher up in the sky falls down close to the ground, we can see those temperatures spike, too. This usually occurs during the very late morning and early afternoon hours. During this time, humidity levels typically fall a bit, but often rise again by the end of the day (we’ll see some real high index values by dinnertime as a result).
However, this time around, we’re lucky to have north breezes drawing cool, dry air into Northeast Kansas. While those temperatures can make leaps and bounds during the day, our nights are quite refreshing. Unfortunately, we will add more humidity to the air by Thursday and Friday. Southwest winds will help to draw hot air in conjunction with the humid air in place, Friday. We could be looking at some toasty heat index values over 100 degrees by Friday afternoon as a result.