Summer in Iowa so far hotter than usual — but not by much

It may seem this summer has been quite a bit hotter than usual.

But state climatologist Harry Hillaker says, overall, this summer has been only slightly hotter than usual in Eastern Iowa.

The average maximum temperature in Cedar Rapids in June — 83 degrees — was about 3 degrees warmer than normal, according to the National Weather Service.

So far this July, the average maximum has been nearly 88 degrees, compared to a normal average high of about 85.

As of July 15, Cedar Rapids has had 15 days with highs at or above 90 degrees, according to the National Oceanic and Atmospheric Administration.

Last summer had a total of 31 days at 90 or above.

Iowa's summer temperatures depend partially on the location of a high pressure system in the western United States.

Explore a year by year timeline of Iowa's summers here.

When the system retreats toward the Southwest, over states like Arizona and New Mexico — as it is now — Iowa won't see as many extreme highs, Hillaker said.

Dust Bowl-type weather comes when the system moves north, he said.

Dry soil is another important factor in temperatures, Hillaker said, since dry soil heats the air faster, leading to higher air temperatures. That cycle can repeat, which is what happened during the Dust Bowl years of the 1930s.

In Iowa, the cooler temperatures and increased moisture in the fall are usually enough to break the cycle, Hillaker said.

In general, since the 1950s, which had some of the coolest summers in recent Iowa history, the state has had more rain, moist air and cloud cover than in the first half of the 20th century, he said.

As a result, Iowans may not experience as many 90-degree days, but the humidity means temperatures stay warmer through the nights.

The most recent stretch of extreme heat came in 2012, with 54 days at or above 90 in Cedar Rapids, the most since 1927.

In 1983, a short but intense drought in early July hurt Iowa crops, as did ones in 1988 and 1989.

The summers of 1934 and 1936 — the Dust Bowl years — are some of the hottest on record in Iowa, Hillaker said. Aug. 18, 1936, remains the hottest August day on record in Cedar Rapids — 108 degrees, according to the National Weather Service.

This weekend, temperatures will hover in the 80s in Cedar Rapids. That relatively mild summer weather should continue for the next two weeks, thanks to a cold front moving across the state, Hillaker said.

90-Degree Days

Here is a look at the years with the most and fewest 90-degree days in the Cedar Rapids area dating back 90 years to 1927, according to the National Oceanic and Atmospheric Administration:

Most

54 — 2012

53 — 1931

52 — 1988

51 — 1934 and 1936

49 — 1930

Fewest

7 — 1958, 1978 and 1996

6 — 1967, 1982 and 2000

5 — 1962 and 2009

4 — 1979 and 2014

3 — 1950, 1951, 1969, 1981, 1992, 1993, 2004 and 2008