Forecasting
QPF Weather Forecast Explained: How Much Rain or Snow Water Is Expected
What quantitative precipitation forecast means, how QPF differs from rain chance, and why snow totals depend on more than QPF alone.
Quick answer: QPF estimates how much liquid precipitation may fall. For snow, QPF is only the water amount before applying snow ratio and other factors.
QPF basics
Quantitative precipitation forecast is usually shown as liquid water. A forecast of 0.50 inches means half an inch of liquid equivalent.
It can come from rain, melted snow, sleet, or mixed precipitation.
Snow connection
Snow totals depend on QPF multiplied by snow ratio, but ratios vary with temperature, crystal type, wind, compaction, and mixing.
That is why the same QPF can produce very different snow amounts.
Flooding use
QPF helps forecasters judge flood risk, especially when heavy rain repeats over the same area.
Soil moisture, terrain, drainage, and storm speed affect whether a given QPF becomes flooding.