A pedestrian using an umbrella to get some relief from the sun walks past a sign displaying the temperature on June 20, 2017, in Phoenix.

It’s become so common, perhaps you’ve stopped noticing how often your local weather forecast is “above normal.” It’s noted during extreme heat in the summer, when mild temperatures persist through the winter, or when nights don’t cool down like they used to.

But on May 4, the hotter Earth will officially become the new normal.

That’s when the National Oceanic and Atmospheric Administration (NOAA) releases its once-a-decade update to “climate normals.” They are the 30-year averages for temperature and precipitation that local meteorologists rely on as the baseline for their forecasts. To be sure, some updates will be minuscule.

But the fastest-warming places will see a real bump in their averages that could make some forecasts seem confusing and pose a challenge to meteorologists.

The current “normals” are from 1981-2010, based on data collected by thousands of monitoring stations around the country operated by the National Weather Service. The NOAA update will shift the time frame for those averages later, to the period from 1991 to 2020. The decade from 2011-2020 is one of the hottest on record in the U.S.

“It was a very substantial upward trend in temperature, especially along the West Coast, in the South and along the East Coast,” says Mike Palecki, with NOAA’s National Centers for Environmental Information.

There were exceptions; some places in the North Central part of the U.S. actually cooled a bit. But globally, the decade ending in 2020 was the hottest decade recorded since 1880.

In Phoenix, Amber Sullins, chief meteorologist at ABC 15, has experienced rising heat in her hometown over her lifetime. Part of that is the urban heat island effect, as the city’s expanding concrete terrain holds more heat overnight.

But the latest National Climate Assessment finds greenhouse gases from human activity are making heat waves more common and drought more intense with some of the highest temperature increases in the Southwest.

Sullins says last summer was especially brutal.

“We set a record of 53 days at 110 degrees or hotter. The previous record was 33 days, so it wasn’t even close,” she says. What’s more, Sullins says that over the entire last decade, Phoenix did not set a single record for low temperature.

After the NOAA update in May, with the baseline for normal shifting to higher temperatures, forecasters in Phoenix and many other places might not be pointing out as many “above normal” days as before.

In fact, some days considered warm now may become officially “cooler” when compared to the new temperature average. Sullins plans to take more time in her daily forecasts to explain the shift.