PlainClimate

Data Methodology

Data Source

All data comes from the NOAA 1991–2020 U.S. Climate Normals — the official 30-year climatological averages published by the National Oceanic and Atmospheric Administration. This is the authoritative U.S. climate dataset, updated every decade.

Data Vintage

The current dataset covers the 1991–2020 period — 30 years of climate observations averaged to produce stable normals. NOAA recalculates climate normals every 10 years. The next update is expected around 2031 when the 2001–2030 period normals will be published.

Station Network

PlainClimate covers 15,492 weather stations across all 50 states, organized under 6,915 cities. Station types include:

  • USW stations — Airport and first-order weather stations with the most complete records
  • USC stations — Cooperative Observer Program stations operated by volunteers
  • US1 stations — Community Collaborative Rain, Hail and Snow Network
  • USS stations — Snow Telemetry (SNOTEL) stations in mountain regions

Variables Covered

  • Monthly and annual average, minimum, and maximum temperatures (°F)
  • Monthly precipitation totals (inches)
  • Monthly snowfall and snow depth (inches)
  • Heating and cooling degree days
  • Humidity and dew point (where available)
  • Wind speed (where available)
  • Growing season length and frost dates (where available)

These variables represent the core climate characteristics that matter most for residential planning, agriculture, construction, and public health. Together they paint a comprehensive picture of what typical weather conditions look like in any given location across the United States.

Processing Pipeline

  1. Raw NOAA Climate Normals files are downloaded from the NCEI data portal.
  2. Station records are linked to cities using NOAA station metadata (station name, state, county).
  3. Monthly values are preserved for all 12 months; annual averages are computed where not provided directly.
  4. Data is loaded into a structured SQLite database indexed by city, state, and station ID.
  5. City pages aggregate available stations; the primary station (typically the airport USW station) drives city-level summaries.

How the Source Agency Collects Data

NOAA Climate Normals are computed from 30 years of weather observations collected through the Cooperative Observer Program (COOP), Automated Surface Observing Systems (ASOS), and other station networks operated by the National Weather Service, the FAA, and volunteer observers. Temperature readings are recorded using calibrated thermometers or electronic sensors following standard siting and maintenance protocols. Precipitation is measured using standard rain gauges, and snowfall is measured using snow boards and snow stakes.

NOAA computes normals using a standardized methodology that accounts for missing data, station moves, and instrument changes. The 1991-2020 normals were computed using the Climatological Linear Relative (CLR) method, which provides more accurate estimates for stations with some missing data compared to simple averaging. Stations must have at least 10 years of data in the 30-year period to be included.

Data Accuracy Commitment

PlainClimate presents NOAA data without modification. Temperature, precipitation, and snowfall values are displayed exactly as computed by NOAA. We do not interpolate data between stations or estimate climate conditions for areas without monitoring coverage. If you find any data that appears incorrect, please contact us and we will verify against the NOAA source data.

Limitations

  • Climate normals are 30-year statistical averages — they describe typical conditions, not weather forecasts.
  • Not all variables are available at all stations. Smaller cooperative stations may only report temperature and precipitation.
  • Station location within a city affects readings. Stations near airports, water bodies, or elevation changes may differ from urban core conditions.
  • PlainClimate is an independent information service and is not affiliated with NOAA or the U.S. government.