EPW Merger

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

1 — Base EPW

Drop an .epw file here, or click to choose

2 — 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.

3 — 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

4 — Merge