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90 Degree Days: How Often Does it Happen?

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This weekend’s weather will be dominated by heat and humidity headlines as we are projected to return to the 90’s for air temperature with heat indices near 100 degrees. For the big 4 in eastern Iowa (Waterloo, Dubuque, Cedar Rapids, Iowa City), we typically see our first 90 degree day in early June (Dubuque middle of June).

Average First 90Average Last 90
WaterlooJune 1stSeptember 4th
DubuqueJune 16thAugust 24th
Cedar RapidsJune 3rdSeptember 3rd
Iowa CityJune 5thSeptember 8th


Parts of eastern Iowa actually saw its first 90 earlier than average when we hit 90 degrees on the nose on May 16th in Waterloo and Cedar Rapids and 91 in Iowa City. Dubuque has yet to hit 90 degrees this year.


Iowa City once again reached 90 on Friday and looks to hit the threshold on Saturday and Sunday, possibly Monday too. Waterloo and Cedar Rapids will likely hit 90 over the weekend. Dubuque is forecast to reach 90 on Sunday.


Over the last 10 years, we average more 90 degree days in July than June. Also using the last 10 years of data, we average as much as 18.4 90 degree days in Iowa City to only 6.2 in Dubuque on a yearly basis.

June 90’sJuly 90’sYearly 90’s
Cedar Rapids3.6x5.0x13.1x
Iowa City4.7x6.8x18.4x

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