A ridge of high pressure is set up over the Central US this week. This ridge with an influx of warmth and moisture into Iowa the next couple of days that will lead to some extreme heat index values.
Dew point temperatures indicate how much moisture is in our atmosphere. As dew points rise to the 60s, we start to feel more stickiness and less cooling. In the 70s, we are in a more tropical air mass with more moisture, making evaporation of sweat more difficult and the body staying warmer.
Dew points will rise in to the 70s both on Tuesday and Wednesday with the numbers being highest on Wednesday. The combination of those high dew points and high temperatures in the mid to upper 90s, dew points could go as high as 110° on Wednesday.
Because of the high temperatures and extremely high heat index values, an Excessive Heat Watch is issued for 10 AM to 8 PM on Wednesday. This is because these conditions increase the likelihood of heat illness and heat exhaustion, if out in the heat too long without taking a break in the air conditioning. Here are some of the signs of heat illness to watch for.
Des Moines has already hit 100° this summer when we made it to 101° on June 17th.