How the site-specific weather file is built
For projects, C4B compiles a typical meteorological year at the exact coordinates from gridded reanalysis: worldwide, ERA5-Land (roughly 9 km), which Open-Meteo blends with ERA5 and ECMWF IFS data; CERRA in Europe (~5.5 km) and NORA3 in northern Europe land-based locations (~3 km). Temperature and humidity are corrected from the model's terrain height to the site's elevation using Copernicus GLO-90 elevation data. Months are selected with the ISO 15927-4 method from the latest 15 complete years in the dataset (2006 to 2020 for CERRA, whose archive in Open-Meteo ends in June 2021). Where two months from different years meet, including December to January, C4B smooths temperature, humidity, pressure, wind speed and cloud cover over the six hours on each side, so the file has no artificial jumps.
Always compared with the nearest station
Every search also uses the nearest weather station file from Climate.OneBuilding.Org (usually TMYx). In a project you can see how the site differs from the station and choose which source to work with.
Custom EPW builder
The Technical and Enterprise plans add a custom EPW builder and EPW downloads:
- Dataset: ERA5-Land or CERRA.
- Year window: 30 years, 15 years or custom.
- Method: traditional (Sandia), TMYx (ISO 15927-4) or entropy-based.
- Presets: typical year, hot year, cold year, seasonal extremes and extreme year.
See your site's climate before design begins
Pin any location and get climate, comfort and preliminary energy insight your whole team can read. Start with a 7-day free trial, or book a 30-minute demo.
Frequently asked questions
Is site-specific data the same as microclimate data?
No. It represents the reanalysis grid cell at the site, from about 3 km (NORA3) to about 9 km (ERA5-Land), and coarser for variables that come from ERA5, corrected to the site's elevation. It can represent the regional climate at the site better than a distant or dissimilar station, but not building-scale effects such as street canyons.
Can I download the weather file?
EPW downloads, including the custom EPW builder and future-climate files, are part of the Technical and Enterprise plans. On other paid plans the site-specific data is used inside C4B's analyses.
What is a TMYx file?
A typical meteorological year built from weather station records with the ISO 15927-4 method, from a station's full record or from a recent 15-year period. For weather stations, C4B uses the files published by Climate.OneBuilding.Org, which are TMYx files for most stations.
Learn the concepts
EPW weather files
What is inside an EPW weather file, where the data comes from, and how to open, check and use one on a project.
Typical meteorological year (TMY)
How typical meteorological years are selected, how TMY, TMYx and ISO 15927-4 reference years differ, and when to use actual or extreme years instead.
Reanalysis data and ERA5
How reanalysis datasets such as ERA5, ERA5-Land, CERRA and NORA3 work, what their resolution means for a building site, and how they compare with station data.
Future weather files and morphing
How morphing combines an observed weather year with climate model projections, how the methods differ and what future weather files can and cannot tell you.
Site climate analysis for architecture
A step-by-step method for the climate layer of an architectural site analysis: where to get the data, what to read, what to put on the sheet and how each finding becomes a design move.
Related features
Future climate scenarios
Future weather files for any year up to 2100 under five SSP scenarios, overlaid on the project's analyses.
Site climate analysis
A full climate study for any location in the world, run in the browser from a single address or map pin.
Precipitation and rainfall intensity
Monthly rain and snow, daily and hourly rain event intensity (15 minutes where recorded), and a long rainfall record in projects.