NWP fields in ProbSevere

A conversation with a forecaster working in the Goodland, KS CWA yielded some good points about the NWP fields in ProbSevere. ProbSevere currently uses data derived from the Rapid Refresh (RAP). ProbSevere uses several analysis/forecast hours to do a 'compositing' for most fields, usually taking the maximum over that time, followed by a spatial smoothing. It uses the F-01, F00, F01, F02, and F03 fields (i.e., the previous analysis, 'current' analysis, and the 1, 2, and 3 hour forecast fields). In this way, when new data arrives, it is 'centered' on the 1-hour forecast time. This is because RAP data typically has about a 1-hour latency from the analysis time. This temporal compositing and spatial smoothing help mitigate timing/placement errors of features or gradients in the NWP data.

The forecaster noted that it might be a good idea to put analysis time in the ProbSevere readout, so forecasters know how old the data are. This would also help inform forecasters if there was a jump in the probabilities, they could discern if it was just new NWP data being incorporated, or if the jump was from changes in the observed radar, satellite growth rates, or total lightning fields. We also discussed the advantages of grouping all the NWP fields together in the readout.

A severe storm in western Kansas, with hail reports of at least 1.75" diameter.