![\"warngen2403\"](\"https:\/\/inside.nssl.noaa.gov\/ewp\/wp-content\/uploads\/sites\/22\/2011\/10\/warngen2403.png\")
<\/a><\/p>\nI used a 60-minute warning duration since the NWS warnings were also about 60 minutes in duration for the TCL storm.\u00a0 I have a re-warning interval of 60 minutes, so that a new warning polygon is issued as the hazard location is nearing the downstream end of the current warning polygon.\u00a0 Because of the buffer around the projected ending point of the threat, each successive warning will have some overlap with the previous warning, which is considered a best warning practice.\u00a0 None of the warnings will be edited for shape based on any county border, because we want to test the effect of warning size and duration without any other factors influencing the warning area.\u00a0 A loop of the warning polygons with the mesocyclone path overlaid:<\/p>\n
Here is the 2×2 table using a 5 km radius of influence (\u201csplat\u201d) around the one-minute tornado observations, I am not applying the Cressman distance weighting to the truth splats, and I\u2019m using the composite reflectivity filtering for the correct nulls:<\/p>\n And the grid point method scores are:<\/p>\n POD = 0.9827 FAR = 0.9771 CSI = 0.0229<\/strong><\/p>\n The FAR and CSI are slightly better than the NWS warnings.\u00a0 However, I’m not trying to compare this method to the actual warnings, but rather as a start to determine the effect of larger and longer warning polygons.\u00a0 So, let’s try that now.\u00a0 Instead of using starting and ending box sizes of 20 and 30 km respectively for our default WarnGen polygon, let’s cast a wider net and quadruple that to 80 and 120 km.\u00a0 The polygon loop would look like this:<\/p>\n And the 2×2 table and scores like this:<\/p>\n POD =1.0000<\/strong><\/p>\n FAR = 0.9962<\/strong><\/p>\n CSI =0.0038<\/strong><\/p>\n What was the effect of the larger longer polygons?\u00a0 Well first, there were no missed grid points, and the POD = 1.\u00a0 But the number of false alarm grid points increased by a factor of about 7, and thus the FAR went up and the CSI went down.\u00a0 Recall that the number of false alarm grid points represents the number of 1 km2<\/sup> grid points accumulated for each minute of data, so the false alarm area and time are much larger, even though these warnings verified perfectly.<\/p>\n So let’s take this in the opposite direction and make our warning polygons smaller.\u00a0 We’ll use starting and ending box sizes of 6 and 10 km respectively.\u00a0 The loop:<\/p>\n and the numbers:<\/p>\n<\/a><\/p>\n<\/a><\/p>\n
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