Climate Change vs. Climate Normals: What the NOAA Baseline Can and Cannot Show

What Climate Normals Actually Measure

A climate normal is the arithmetic mean of a weather variable (temperature, precipitation, snowfall, etc.) over a 30-year period. The World Meteorological Organization (WMO) sets the standard, and NOAA calculates U.S. normals using data from over 15,000 weather stations. The current 1991-2020 normals replaced the 1981-2010 set in 2021.

The 30-year averaging period smooths out year-to-year variability (El Niño, La Niña, volcanic eruptions) to reveal the underlying climate pattern. This makes normals excellent for comparing one location to another, which is the primary use case on PlainClimate. But the smoothing also obscures trends: a location where temperatures have been rising steadily gets a single average number that understates recent conditions and overstates older ones.

Where the Normals Lag Reality

What it tells you: The 1991-2020 normals accurately reflect average conditions over that 30-year period. For most practical purposes, deciding if a city has mild winters, heavy snow, or high humidity, they are reliable and useful.

What it doesn't tell you: Temperatures in the most recent decade (2011-2020) are significantly warmer than the 1991-2000 decade that anchors the other end of the average. A city whose 30-year average July high is 92°F may have actually averaged 94-95°F in the most recent 5 years. For heat-sensitive relocation decisions, the normal understates what you are likely to experience.

How to use it: Use normals on PlainClimate city pages for relative comparison - "Is Phoenix hotter than Las Vegas?" - and add a mental adjustment for recent warming. NOAA publishes supplemental "recent averages" (typically 15-year or 5-year windows) that better capture current conditions. For heat days, precipitation extremes, and snow trends, our extreme weather guide provides additional context.

Regional Warming Patterns

What it tells you: Warming has not been uniform across the U.S. Alaska has warmed dramatically, some stations show average temperature increases of 3-5°F compared to the previous normals period. The northern Great Plains, Mountain West, and desert Southwest have also warmed substantially. The Southeast has warmed the least, with some stations showing minimal change.

What it doesn't tell you: National or regional averages mask extreme local variation. Coastal cities with maritime influence may warm less than inland cities. Urban heat islands amplify warming in densely developed areas. The normals capture station-level data but do not break out urban vs. suburban vs. rural variation within a metro area.

What This Means for You: A Practical Framework

Step 1, Use normals for comparison. Browse state pages and city profiles on PlainClimate to compare climates. The normals are the most reliable baseline for side-by-side comparison because they use a consistent methodology across all stations.

Step 2, Add a warming adjustment for hot climates. If you are evaluating a city in the Sun Belt or desert Southwest, assume that average high temperatures in summer are 1-3°F warmer than the normals suggest. The difference matters for livability, the gap between a 100°F average and a 103°F average affects energy costs, outdoor comfort, and health risks.

Step 3, Check precipitation trends separately. Precipitation is changing in complex ways, some areas are getting wetter, others drier, and many are experiencing both more droughts and more intense storms. Climate normals average all of this into a single annual precipitation figure that may not capture increasing variability.

Step 4, Consult climate projections for long-term decisions. If you are making a 20+ year decision (buying a home, planning retirement location), the NOAA normals describe the recent past. For forward-looking climate information, consult the NOAA Climate.gov portal and state climate office projections.

Where the Normals Best Support Specific Decisions

Comparing two cities side by side

This is the strongest use case for the normals. Both temperature and precipitation values are computed with the same WMO methodology across all 15,000+ contributing stations, so a Phoenix-vs-Miami comparison rests on apples-to-apples math. Use the city profiles directly and look at monthly profiles, not just annual averages.

Estimating energy demand

Heating and cooling degree days from the normals approximate average annual HVAC load. Pair them with a local utility's per-degree-day rate to estimate annual cost.

Worked example: Denver vs Phoenix HVAC swap

A homeowner relocating from Denver, CO (1991-2020 normal: about 5,900 heating degree days, 850 cooling degree days) to Phoenix, AZ (about 875 HDD, 4,765 CDD) effectively trades winter heating cost for summer cooling cost. At Denver's natural-gas rate of $1.10 per therm and a 65% efficient furnace, 5,900 HDD costs roughly $1,370 per year. At Phoenix's electricity rate of $0.14 per kWh and a SEER-15 air conditioner, 4,765 CDD costs roughly $2,000 per year. The 46% increase in HVAC budget is invisible if you only compared annual mean temperatures (51.2°F vs 75.6°F) without converting to degree days.

Estimating frost dates for gardening

Frost-free days and last-spring/first-fall freeze dates from the normals are reliable inputs for cultivar selection. Add a 7-10 day buffer to the published last-spring freeze date for cold-sensitive plants.

Where the normals fall short

Use case	Reliability	Recommended supplement
Side-by-side city comparison	High	None needed
HVAC budgeting	High	Local utility rate
Crop-suitability planning	Medium	USDA hardiness map
20-year retirement decision	Low	Climate projections (NOAA Climate.gov)
Wildfire-smoke exposure	Not covered	PurpleAir + EPA AirNow

Frequently Asked Questions

Do NOAA climate normals account for climate change?

Climate normals capture the cumulative warming within the 30-year period but do not project future trends. A city may already be experiencing temperatures warmer than its normals suggest.

When will NOAA publish new climate normals?

The next update, covering 2001-2030, is expected around 2031. The current 1991-2020 normals remain the standard until then.

How much warmer are the 1991-2020 normals compared to the previous set?

Nationwide average temperature increased approximately 0.5°F compared to the 1981-2010 normals. Alaska and the northern Great Plains show the largest increases. Winter temperatures have increased more than summer temperatures in most regions.