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Weather Data File Types

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Representation and storage of short-term weather data have evolved along with the computer and information revolution of the last 40 years.[1] This page summarizes different data sets and file formats of weather data.

Data sets of weather data

The table below lists typical year weather data available on the internet. Most data sets can be downloaded from DOE2.com.

Data Set Full Name Derived from Covered Locations
CTMY Canadian TMY Canadian Government data 12 Canadian locations
CTMY2 Canadian TMY 2 Canadian Government data 40 Canadian locations
CTZ2 California Thermal Zones 2 Supplied by the California Energy Commission in 1992 16 California zones
GBRI[5] GRIdded Binary Standardized by the World Meteorological Organization to store historical and forecast weather data
TMY Typical Meteorological Year US NOAA NCDC data sets 238 US locations
TMY2 Typical Meteorological Year 2 US DOE NREL data sets 238 US locations
TMY3 Typical Meteorological Year 3 US DOE NREL datasets 1,200 US locations
TRY Test Reference Years US NOAA NCDC data sets 60 US locations
IWEC[2] International Weather for Energy Calculations US NOAA NCDC data sets 227 locations outside the USA and Canada
WYEC ASHRAE Weather Year for Energy Calculations US NOAA NCDC data sets 51 US locations
WYEC2 ASHRAE Weather Year for Energy Calculations US NOAA NCDC data sets 51 US locations

Typical Meteorological Year (TMY) weather data

The geographical coverage of the TMY3 ground stations in the US.[4]

A Typical meteorological year (TMY) is a collation of selected weather data for a specific location, generated from a data bank much longer than a year in duration. It is specially selected so that it presents the range of weather phenomena for the location in question, while still giving annual averages that are consistent with the long-term averages for the location in question. The latest TMY weather data sets, TMY3, are data sets of hourly values of solar radiation and meteorological elements for a 1-year period. Their intended use is for computer simulations of solar energy conversion systems and building systems to facilitate performance comparisons of different system types, configurations, and locations in the United States and its territories. Because they represent typical rather than extreme conditions, they are not suited for designing systems to meet the worst-case conditions occurring at a location. The source data are available for download from the National Solar Radiation Data Base.

File formats of weather data

Early automated data formats of weather data replicated punched card layouts formerly used for data entry by weather services. To save transcription cost, often data from only every third hour were made available. High cost, inconvenient formats, and omitted data made for difficult application to simulation. Until recently, sources files of weather data typically consist of 8,760 fixed format records (values located in specific columns of each data line). Current formats, such as TMY3 and EPW, are now more compatible with desktop spreadsheet tools. They are comma-separated and include metadata (such as site location) and column headings that make them somewhat self-documenting.

Format Description Applications Sample Download
.EPW EnergyPlus weather files EnergyPlus, ESP-r Epw.PNG EnergyPlus
.DDY ASHRAE Design Conditions Design Day Data file Ddy.PNG EnergyPlus
.BIN Binary data eQUEST, DOE-2 Bin.PNG DOE2.com Whitebox
.STAT Summary report Directly read from Notepad Stat.PNG EnergyPlus
.CSV Spreadsheet data for TMY3 files Spreadsheet-based and home-coded tools Tmy3.PNG NREL
.WEA Weather Tool data originally developed by Autodesk for Ecotect Ecotect, Weather Tool Wea.PNG Install Ecotect
.TMY2 TMY2 data in ASCII format TRNSYS Tmy2.PNG NREL

Weather file format conversion

  • EnergyPlus Weather Statistics and Conversions: A utility in the EnergyPlus installation package
  • TMY3toTMY2: A utility developed by NREL
  • eQ_WthProc: Convert EnergyPlus EPW Files into eQUEST and DOE-2 BIN Files
  • DOEWth: Convert NOAA/NCDC and Other Common Format Files into eQUEST and DOE-2 BIN Files
  • .xls to .bin


[1] C. S. Barnaby and D. B. Crawley, "Weather data for building performance simulation," in Building Performance Simulation for Design and Operation, J. L. M. Hensen and R. Lamberts, Eds., ed Oxford: Spon Press, 2011.

[2] IWEC, Building Energy Software Tools Directory, available at: http://apps1.eere.energy.gov/buildings/tools_directory/software.cfm/ID=369/pagename=alpha_list

[3] Weather Data & Weather Data Processing Utility Programs, DOE2.com, available at: http://doe2.com/index_wth.html

[4] National Solar Radiation Data Base, 1991- 2005 Update: Typical Meteorological Year 3, available at: http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/

[5] World Meteorological Organization, A GUIDE TO THE CODE FORM FM 92-IX Ext. GRIB, available at: http://www.wmo.int/pages/prog/www/WDM/Guides/Guide-binary-2.html

See also

Weather Data Sources