How the heads-up flag works (beta)

• Heavy rain: Open-Meteo forecasts at least 50 mm of rain over the next 3 days (today plus 2) at the town, or at either of the two nearest towns upstream on our list.
• Rise outlook: our 7-day rise outlook (unchanged, pre-registered model) gives at least a 25% chance of a rise, and the outlook is public for that gauge.
• Heads-up = both. Rain to watch = heavy rain only. Weather older than 36 hours is not used.
• This rule has not been backtested. It is a plain combination to prompt people to check official sources. It is not an official warning.