The five hottest September days in Salt Lake City's record were all set this year, so it isn't a surprise that last month shattered the record for the warmest September on record.

Salt Lake City ended September with an average temperature of 75.1 degrees Fahrenheit, blasting the previous record set in 1990 by 3.1 degrees, according to National Weather Service data and records.

The final average also ended up 6.7 degrees above the 30-year normal. The agency has kept track of the city's weather information since 1874.

The average maximum temperature, or the average of how hot it got each day, ended up at 87.8 degrees, narrowly edging 1979's record of 87.5 degrees. Salt Lake City's September 2022 average was propelled by seven 100-degree days to start the month, including a new monthly record of 107 degrees set on Sept. 7, which also tied the all-time hottest temperature ever recorded in the city.

Salt Lake City only had three 100-degree September days on record prior to this year.

The city also set a new minimum temperature record — the average of how cool it got each day. Salt Lake City's minimum temperature topped out at 62.4 degrees, snapping the previously 139-year-old record of 60 degrees set all the way back in 1883.

The record-breaking September tacks onto a particularly warm stretch in the city this year, which also includes:

  • The hottest month on record: July's average was 87.3 degrees, besting the previous record of 85.7 degrees set in July 2021
  • The hottest summer on record: 81.5 degrees, beating the old record of 80.9 degrees set in 2017
  • The most 100-degree days in a year: 34 (the previous record was 21, which occurred three times)
  • The second-longest streak of consecutive 100-degree days: 9 (one day shy of the record set in 2003)
  • The second-longest streak of consecutive 90-degree days: 42 (eight days shy of the record set in 1967)

How reliable is the data?

All of these records also prompted some online skepticism of the weather service's observation data collecting, which the agency defended in a series of social media posts during the September heat wave.

Salt Lake City's official weather data, including precipitation and temperature information, is collected at a station by the Salt Lake City International Airport. That's been the case since 1928, two years before the city renamed the airport from Woodward Field to Salt Lake City Municipal Airport. Federal meteorologists had recorded at a few different downtown locations from 1874 up until 1928.

The airport has grown immensely since 1928, though. Some posted online that concrete and asphalt at the airport today are causing an urban island heat effect, which is boosting the temperature records at the airport.

For its part, meteorologists at the National Weather Service said, yes, temperatures can vary up to about 5 degrees depending on where you are in Salt Lake City; however, the agency contends some of the heat is representative of changes around the city and valley. The county's population has jumped nine times as a result of massive development over the past nine decades, per the U.S. Census Bureau.

But meteorologists explain that the airport also has the lowest elevation in the Salt Lake Valley and the northwest quadrant has "few to no trees or vegetation." Meanwhile, the record-low levels of the Great Salt Lake mean there is almost no summer lake breeze to help cool down temperatures like in the past. Then there's the shift in the American West's climate, which includes the airport location.

All of these factors, they said, can also explain why the airport is experiencing hotter temperatures, including some of the temperature variations within different parts of the city.

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"The Salt Lake City airport temperatures represent the environment and land use across this portion of the county," they wrote in a statement on Sept. 1. "While downtown and other areas may see temperatures that differ by 2 (to) 5 degrees, looking at long term trends, temperatures all over the valley are being impacted by a combination of climate change, urbanization, Great Salt Lake levels and land use changes."

Then, on Sept. 7, the agency wrote that it "did not find any definitive empirical evidence proving a positive bias in the temperature readings from calibration or site characteristics" during a test of five sensors in and around the airport on the hottest day of September, meaning that meteorologists didn't believe there was anything wrong with the temperature sensors to result in the higher temperatures.

In short, it stands by the data.

"This is not to say that we are writing off the possibility of these factors influencing the temperature readings, and we will continue to maintain awareness of any future discrepancies," the weather service added, at the time. "Going forward we plan to work with our partners to discuss site considerations with the continued development in the area of the official station."

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