EPW merger

Patch a base EPW with Open-Meteo historical data. Runs in your browser — the file never leaves your machine.

Base EPW

Base EPW Choose or drop an .epw file

Location

Latitude

Longitude

Model

Pre-filled from the EPW header when a file is loaded. Edit if you want a different point — the LOCATION header of the patched file is rewritten to match. The time zone and elevation in that header are kept as they are.

Days to replace

Start date

End date

Extra hour shift

Rows are matched by month/day/hour, so the year of the range only selects which real weather is downloaded. Times are converted from UTC to the EPW time zone automatically; the extra shift is for DST or manual alignment. Dates run from 1950 to today; the archive itself trails real time by about five days, so the most recent dates may come back empty.

Update GROUND TEMPERATURES header for the months covered

Merge

Load a base EPW, choose a range and run the merge. The patched file downloads when it is ready.