Washing before rain can still make sense if you're removing salt, film, and grit — but the key is whether you can finish the job before precipitation arrives.
What to look for
- Low rain probability in the next hour.
- No obvious showers in the hourly forecast.
- Enough time for a proper dry to avoid spotting.
If rain is likely soon
Do a quick rinse + contact wash of the dirty areas, then dry. If the forecast looks showery, consider saving a full wash for a better window and just rinse salt and grime off the lower panels.