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2018 was less warm and wet than recent record-setting years in St. Louis, but still exceeded historic averages

2018 was less warm and wet than recent record-setting years in St. Louis, but still exceeded historic averages

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J.B. Forbes Best of 2018

FILE PHOTO: A couple walks down the steps of the Old Courthouse on Monday, March 26, 2018, on a wet, rainy day in the St. Louis region. Photo by J.B. Forbes, jforbes@post-dispatch.com

At a glance, it might look as if 2018 was a relatively “normal” year for St. Louis in terms of climate data: The average annual temperature was 57.3 degrees, according to the National Weather Service’s local forecast office — just higher than the 57.1-degree average from 1981 through 2010.

But seemingly normal averages can be made up of seesawing extremes that balance out, and that was the case with area weather in 2018, as multiple months saw record or near-record heat, while others saw the same for cold temperatures.

“Temperature-wise, it was very unusual, in terms of it had a lot of ups and downs,” said Jayson Gosselin, a local meteorologist for the NWS, summarizing 2018.

Those extremes were highlighted by St. Louis’ fourth-coldest April ever recorded, immediately followed by the hottest May since official records began in 1874.

“It was almost a we-went-from-winter-to-summer kind of thing,” Gosselin said.

The city also experienced its eighth-warmest June on record, and eventually its sixth-coldest November.

Although those occasional bursts of cold helped dial down the year-end average temperature, 2018 certainly didn’t lack for heat. St. Louis recorded its second-most daily high temperatures that were “at or above” 80 degrees, Gosselin said, with 148 days topping the mark.

And while the area’s 2018 mean temperature just about matched the 30-year average from 1981 to 2010 — the most recent interval that the NWS uses for historic comparisons — it was distinctly warmer than the agency’s older data. From 1951 to 1980, for example, average annual temperatures in St. Louis were nearly two degrees lower, at 55.4 degrees. (More detailed comparisons to past climate trends could not be examined, since data from the National Oceanic and Atmospheric Administration cannot currently be found online because of the ongoing government shutdown.)

Plenty of recent years have seen bigger, and even record-setting, anomalies for warmth.

“The three warmest years (recorded in St. Louis) are all within the last seven,” Gosselin said. 2012 saw a record average of 61.2 degrees, while 2016 (60.4 degrees) and 2017 (60.2 degrees) were the second- and third-hottest years the city’s record books have seen.

A more normal one-year average such as 2018’s does not alter the overall warming trend — one that has been strongly felt worldwide as a result of climate change that is clearly attributed to human activity.

“Weather doesn’t follow a linear progression. Although we’re in a period of warming and increased precipitation, there’s going to be fluctuations from year to year,” said Andrew Hurley, a professor of history at the University of Missouri-St. Louis with a specialty in environmental history. “What we consider to be a cool year in a recent context, it’s still above average in a historic context.”

St. Louis’ 2018 precipitation totals, meanwhile, were “a little wetter than usual,” said Gosselin, with 42.60 inches measured, compared with 40.96 inches on average. But when it did rain, it poured, as the 57 days with at least a quarter inch of precipitation tied for eighth on the city’s list of such occurrences. That is consistent with a broader climate trend of heavy downpours becoming more common nationally, and particularly in regions such as he Midwest.

Gosselin said that overall, wet conditions had prevailed in recent years, and that 2015 ranked as the city’s wettest year on record.

“In general, warmer air can hold more moisture. So, yes, that is not too terribly surprising,” Gosselin said, describing the wet trend of the recent past.

Other types of precipitation extremes were seen elsewhere in the region. Only a couple hours to the west, Columbia saw the driest April on record, and its 11th-driest spring, overall. In that area, Gosselin said precipitation was below normal in May, June and July, so drought conditions “kind of kept building” — something drought-ravaged farmers around the state were painfully aware of last growing season.

The hot, wet conditions that have become more common in the region can present especially steep challenges for cities like St. Louis, Hurley said — where heat is exacerbated by the urban heat island effect, and precipitation challenges are made worse by the amount of impervious surfaces.

“The type of urban life we’ve constructed ... can make changes more dramatic and amplify the effects of warming and moistening,” he said.


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