• Each fall has a typical flow for every month, from park and guide information: snowmelt falls peak in late spring, and eastern rain-fed falls run low in late summer.
• Recent rain: the last 30 days of rain, with recent days counting most, compared with the same weeks in the last 3 years.
• How much recent rain matters depends on the fall's type: most for rain-fed, some for snowmelt, little for big rivers, and almost none for spring-fed or dam-regulated falls.
• Forecast: rain in the next 10 days is fed forward, so you can catch a fall roaring after a storm.
• Five straight days below −3 °C flags ice formations. Strong flow plus sun flags a chance of rainbows in the spray.

An estimate from weather data (Open-Meteo), not a flow gauge. After heavy rain, trails and pools can be dangerous: stay behind barriers and away from the brink.