Why Mid-Missouri’s drought is fueling abnormal warmth this fall

If you stepped out the door early this morning, you almost certainly at least grabbed a light jacket. But by the time you were driving home this afternoon, you were probably rolling the windows down or cranking up the air conditioning. Mid-Missouri started the day in the crisp low 50s, and rocketed straight up to the upper 70s by the late afternoon.

That is a massive 25-degree temperature jump in just a matter of hours. While chilly mornings are exactly what we expect as we head deeper into late October, these huge afternoon rebounds are a direct result of a hidden problem beneath our feet.

To understand why our afternoons still feel like September, we have to look at the worsening drought. The latest Missouri Drought Monitor shows significant swaths of Mid-Missouri trapped in severe to extreme drought, particularly along the I-70 and Highway 63 corridors, and down south toward the Lake of the Ozarks and Fort Leonard Wood. The lack of rain over the past two months has left our topsoil completely baked. That missing soil moisture is now hijacking how the sun heats our local atmosphere.

It all comes down to a daily battle between the sun and the soil. During a normal, wet fall, solar energy hits damp ground. A huge portion of the sun's energy is forced to evaporate the water trapped in the dirt. This process is known as "latent heat". Because the sun is working overtime just to evaporate that moisture, there is much less energy left over to actually warm up the air. The wet ground acts like a natural air conditioner, keeping our afternoon temperatures in check.

But look at the reality across Mid-Missouri right now. With our topsoil cracked and dry, there is absolutely zero moisture left to evaporate. Because of this, all of the sun's energy becomes what we call "sensible heat." Instead of evaporating water, the sun aggressively bakes the dry dirt, which immediately transfers that heat to the air right above it. Without soil moisture acting as a buffer, our temperatures are free to skyrocket the second the sun comes up. Furthermore, this extremely dry air cools off much faster at night, which is exactly why our mornings are still dropping into the low 50s.

So, when will this rollercoaster flatten out? This weekend, there is little to no chance of precipitation in the forecast, so the underlying physics of this heating problem will not be solved. Until we get a significant, slow-soaking weather system to drive moisture deep into the ground or a cold front to bring lower temperatures, these more noticeable temperature swings are locked in place.

For now, expect these quick 25-degree daily swings to continue straight through the weekend and into next week as the dry ground continues to play a role in dictating our local weather.