PlainClimate

Data sources

Every figure on PlainClimate comes from one of these public sources, each linked.

First published · revised

The sources

  • U.S. Climate Normals, 1991-2020, NOAA National Centers for Environmental Information. Monthly, daily, hourly and annual normals, day counts, frost probabilities, for about 15,000 stations. Released May 2021, 23 stations reissued 2023. Next set: 2001-2030.
  • U.S. Monthly Gridded Climate Normals, 1991-2020 (nClimGrid, accession 0245564), NOAA NCEI. Monthly high, low, mean and precipitation normals on a grid of about 5 km over the 48 states, interpolated by NOAA from station records. Used only for the places of 50,000 or more without a station of their own and their ZIP areas, beside the station records; checked against five big-city airports (highs within about 1°F, lows 1-6°F cooler on the grid).
  • POWER solar climatology, 2001-2020 (CERES SYN1deg), NASA Langley Research Center. All-sky and clear-sky sunshine reaching the ground, monthly, on a 1-degree grid. Their ratio is the sunshine share on place pages and in the sunniest and cloudiest rankings. These data were obtained from the NASA Langley Research Center (LaRC) POWER Project funded through the NASA Earth Science/Applied Science Program.
  • Plant Hardiness Zone Map, 2023, ZIP code listings, USDA Agricultural Research Service; data by the PRISM Group, Oregon State University (https://prism.oregonstate.edu, accessed October 8, 2026). The USDA zone of every ZIP code area, which leads the zone answer on place pages and in the frost tool; quoted as text, not redrawn as a map, and not included in downloads. The listings are the property of Oregon State University, used under its terms; they are not U.S. government works.
  • State Climate Extremes Committee records, NOAA NCEI. Each state's official all-time highest and lowest temperature, greatest 24-hour precipitation and snowfall and deepest snow, on the state pages.
  • Subcounty population estimates, Vintage 2024, U.S. Census Bureau. The population of New England towns, shown beside the smaller census-designated place of the same name.
  • ZIP Code Tabulation Area to place relationship file, 2020, U.S. Census Bureau. Which ZIP code areas lie in which city, for the ZIP rows on those cities' pages.
  • Normals calculation methodology, NOAA NCEI. How the normals are computed, completed and adjusted.
  • Applied Climate Information System (ACIS), NOAA Regional Climate Centers. Station histories from GHCN-Daily and the NWS threaded city records: monthly extremes with dates, means, precipitation and snowfall. Read again when the database is rebuilt.
  • nClimDiv statewide series, NOAA NCEI. Statewide monthly temperature and precipitation since 1895, area-weighted. File version of September 4, 2026.
  • nClimDiv data files, NOAA NCEI. The files behind the statewide pages.
  • Population estimates and Gazetteer, U.S. Census Bureau. Vintage 2024 place populations, ACS 2019-2023 for census-designated places, place and ZIP centers (2024 Gazetteer).
  • USDA Plant Hardiness Zone Map (2023), its method, U.S. Department of Agriculture, Agricultural Research Service. The zone rule PlainClimate applies to each station's own 1991-2020 coldest nights (from ACIS): zones 10°F wide from -60°F, each split into a and b, giving each station's own zone beside the map's ZIP zone. The map is not redrawn.

Refresh

The normals change once a decade. Station histories and the statewide series are read again when the database is rebuilt (the current edition runs through August 2026); the date of the file in use is on the methodology and data pages.