Methodology
We publish one metric, against one reference, with the baselines named. This page states what produced every number on the site.
The metric
The Critical Success Index (CSI) counts, for a given rain-rate threshold and lead time, the grid cells where the forecast and the observation agree on rain. CSI = hits / (hits + misses + false alarms). It ignores correct "no rain" cells, so it cannot be inflated by dry weather. 1.0 is perfect; 0 is no skill.
CSI = hits / (hits + misses + false alarms)
The reference
Forecasts are verified against NOAA MRMS precipitation rate, regridded to the same 4 km grid as the forecast.
The baselines
- Optical Flow
- Extrapolates the latest radar field along its motion. The standard nowcasting method.
- HRRR
- NOAA’s High-Resolution Rapid Refresh, the best-in-class numerical weather prediction model for the US.
- Persistence
- Assumes the current rain field does not change. The floor any nowcast must beat.
Inputs
The live product uses NOAA MRMS radar and NOAA GOES satellite observations. Each published evaluation lists the inputs of the model version it measured.
Results
Figures appear here once the current evaluation is final.
Europe
The European product uses EUMETNET OPERA radar. Its evaluation will be published separately, on the same method.
Make the call with the forecast in hand.
Tell us the decision you make and where. We will show you the forecast on your own past events.