I can tell you for sure that the standards, such as they are, vary greatly from office to office and maybe even from forecaster to forecaster in a given office. Out here in CT I've seen some storms get T-warned recently that would've just been laughed at had they occurred out on the Plains. I'm talking about blatantly obvious outflow dominant cells that didn't even have much in the way of a sustained couplet. At the time I figured these warnings must have been based on some kind of eyewitness report, however spurious, but the text just said it was doppler indicated with no mention of any spotter reports. Let's face it, the TVS algorithms are far from perfect, we all know this. Someone should tell those guys that a momentary TVS just doesn't really indicate all that much in the absence of any kind of sustained storm-scale rotation. I suspect most of these kind of dubious radar-indicated warnings are probably driven more by the "CYA" effect than anything else. No one at OKX seems to want to take any chances, not with the super-high population densities we have here in the Tri-State/NYC Metro areas. Ironically, the one recent storm that did actually produce a tornado in CT wasn't T-warned until 10 minutes after the tornado lifted. That cell did indeed exhibit classic sustained supercellular characteristics on radar, but it probably lacked a TVS at the time of the tornado and thus apparently wasn't warned. The bottom line seems to be that there are no hard and fast rules for doppler indicated warnings. It would appear that it's pretty much up to the forecaster on duty whether to warn or not.
