Official 'climate normals' confirm winters in the U.S. are getting warmer

Winters that once felt bitterly cold in many U.S. cities now pass with fewer freezing nights. January temperatures are about one degree Fahrenheit higher in many places compared to what they were a few decades ago.

The numbers come from U.S. Climate Normals, the official 30-year averages that define what counts as typical weather for each station.

The current dataset covers 1991 to 2020, and provides a baseline to compare today’s conditions with the recent climate in each area.

How climate normals work

The research was led by Dr. Anthony Arguez, a climatologist at NOAA’s National Centers for Environmental Information in Asheville, North Carolina (NCEI).

At the core of this study are the 30-year climate normals, which are calculated using long records from almost 15,000 U.S. weather stations.

According to NOAA, the normals cover monthly, daily, and hourly statistics for temperature, precipitation, snowfall, and many related measures.

To build reliable values, scientists update the normals every ten years and adjust for station moves, equipment changes, and gaps in observations.

One technical paper explains how 30-year averages are built from checked station data using methods that link daily, monthly, and yearly values.

“NOAA’s 1981-2010 Climate Normals represent the latest decadal installment of 30-year averages,” wrote Arguez.

That earlier installment laid the groundwork for the newer set from 1991 to 2020, which now defines the modern climate baseline.

Key climate metrics are shifting

In most regions across the United States, the 1991 to 2020 normals are warmer than those recorded between 1981 and 2010.

NOAA’s maps show that January temperatures are about 0.5 to 1.5 degrees Fahrenheit (0.3 to 0.8 degrees Celsius) higher across wide areas, while only a few north-central pockets cooled slightly.

The United States, as a whole, has warmed at about 0.17 degrees Fahrenheit ().09 degrees Celsius) per decade since 1901. The estimate comes from a long-running indicator maintained by the Environmental Protection Agency (EPA).

When a city warms, several key climate metrics shift together. One of the clearest is a drop in heating degree days, which track how much daily temperatures dip below a defined baseline.

Station-based normals are only part of the picture. For mapping, the numbers rely on nClimGrid, a detailed grid that blends station data into 2.5 mile (4 kilometer) squares across the country.

Monthly gridded normals are available for 1991 to 2020 and for 2006 to 2020. The longer 1901 to 2000 baseline reveals how typical temperatures and precipitation have shifted over the past century.

Daily gridded normals add even more detail. They allow researchers to compute anomalies – differences between actual weather and the usual value for that date.

Capturing El Niño’s fingerprint

One twist on the normals uses El Niño Southern Oscillation, a recurring Pacific Ocean warming and cooling pattern that steers weather.

The pattern’s warm and cool phases strongly influence winter and spring conditions across large parts of the United States.

A more recent analysis provides separate monthly climate normals for five ENSO phases, from strong La Nina to strong El Niño .

For each phase, the product also lists percentile values that show how often temperature or rainfall falls in the wettest or driest 10 percent.

Instead of using a strict 30-year average, the ENSO normals rely on a 15-year running average. That approach helps separate the influence of shifting Pacific Ocean patterns from the broader rise in temperatures over land.

Why climate normals matter

Alongside the traditional 30-year values, NOAA now publishes supplemental 15-year normals for 2006 to 2020 at many stations.

These shorter averages respond more quickly when temperatures or rainfall patterns change, although they also wobble more from decade to decade.

Energy planners often look closely at those 15-year statistics. Their decisions about capacity and grid upgrades depend more on the climate of the next decade than on distant history.

In many large U.S. cities, the latest normals say that recent winters have, on average, been milder than a few decades ago. That does not erase local quirks, but it means a typical winter night today is warmer than many parents remember.

The same archive shows that much of the eastern two-thirds of the country has become wetter in recent decades. The Southwest has trended drier in both winter and summer.

Lessons from new climate normals

According to a National Weather Service overview, NCEI is the world’s largest active archive of weather data. That huge record makes it possible to track these shifting patterns across the entire nation.

Because normals influence nearly every sector, even subtle changes ripple into daily life.

Airlines revise deicing schedules, allergy forecasts shift with changing pollen seasons, and building codes gradually adapt as local heat and rainfall patterns evolve.

The next installment of U.S. Climate Normals, based on 2001 to 2030, will arrive in the early 2030s.

If greenhouse gas emissions remain high, future averages will likely show that conditions, once considered extreme in many cities, have become the new normal.

Information taken from the U.S. Climate Normals reported by the National Centers for Environmental Information.

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