As the jet stream lifts to the north a “heat dome” will bring an extended period of hot weather to much of the United States. Below is a model’s interpretation of the height of the middle of the atmosphere. Taller heights are caused by warmer temperatures. You can see a clear division between the bottom two thirds of the U.S. with taller heights (hot temperatures) and the upper third of the U.S. with lower heights (just warm temperatures). This is just one way of visualizing the heat on the way.
An Excessive Heat Watch and Warning has been posted for our area from Wednesday into Saturday with heat index values ranging from about 100 to 110 degrees when you factor in the humidity.
While our forecast high temperatures won’t break records, it will be the heat and the humidity combination that will make things feel so hot.
What will make this event dangerous is the lack of cool air at night with lows in the middle to upper 70’s. Below are the record highest minimum temperatures compared to the forecast temperatures from Wednesday the 17th through Saturday the 20th.
With temperatures starting off so warm in the morning, we don’t have much to go to reach the 90’s. Everyday from Wednesday through Saturday is forecast to hit at least 90 degrees with temperatures peaking into the middle and upper 90’s for some. Here is how many times we have hit 90 so far this year:
*Through July 15th
Compare that to last year’s 90 degree days:
Besides Iowa City who saw 7 consecutive 90+ days this year from 6/30 to 7/6 and Waterloo who saw 4 consecutive 90+ days from 6/29 to 7/2, we haven’t had a 3+ day stretch of this kind of heat area-wide. This upcoming 4 day run of 90 degree plus weather is comparable to a 90+ degree stretch that we had last year in 2018.
If you are wondering the longest ever stretch of 90 degree days can be found below: