Our Data Source
All climate data on City Weather Data is sourced from the NOAA Climate Normals 1991-2020 dataset, maintained by the National Oceanic and Atmospheric Administration (NOAA).
Climate Normals represent 30-year averages of weather observations, providing a reliable baseline for understanding typical climate patterns at any given location. The 1991-2020 period is the most recent standardized climatology period adopted by the World Meteorological Organization.
Data Processing
Our data pipeline processes NOAA Climate Normals through several stages:
- Data Extraction: We download official NOAA Climate Normals data files for US weather stations
- Quality Control: Data is verified for completeness and accuracy
- City Mapping: Weather stations are mapped to their corresponding cities
- Metric Calculation: We compute 8 key climate metrics from the raw observations
- Formatting: Data is structured into JSON format for web delivery
Climate Metrics Explained
📊 8 Core Metrics
- Temperature: Monthly average highs, lows, and mean temperatures
- Precipitation: Monthly and annual rainfall totals with percentiles
- Snowfall: Monthly and annual snowfall accumulation
- Snow Depth: Average snow depth on the ground
- Degree Days: Heating and cooling degree days for energy planning
- Temperature Extremes: Record highs and lows, frost dates
- Precipitation Days: Frequency of measurable precipitation
- Frost Probability: Likelihood of frost occurrence
Data Limitations
While we strive for comprehensive coverage, some limitations exist:
- Not all cities have weather stations with complete 30-year records
- Some metrics may be unavailable for certain locations
- Data represents historical averages, not current conditions or forecasts
- Coverage is limited to the United States
Data Updates
NOAA Climate Normals are updated every 10 years. The current 1991-2020 normals will be the standard until the 2001-2030 normals are released in 2031. We update our database as new cities are added or data quality improvements are made.