In article , Harold Brooks wrote:
In article ,
says...
I have watched the refreshing screen the NWS has for all the watches
and warnings for severe storms and tornadoes. I have noticed that at
times they will display, over a period of many hours, many dozen
tornado warnings as red dots. However, when I check the pages with the
actual storm reports on the following days, it shows only a few. In
fact, in appears that of all those tornado warning dots, that perhaps
10 and at most 15% of those tornado warnings actually formed a
tornado.

Now, if this is in fact true, then what about those tornadoes that are
confirmed where a warning was _never_ even issued?

What is the accuracy rate of [issued tornado warning vs confirmed
tornadoes]?

Also, what is the percentage of times when an actual tornado hits the
ground _but_ was never associated with a warning?

Here are the annual tornado warning statistics for the US from 1986-
1994. POD is the probability that a tornado will have a warned county
associated with it. FAR is the false alarm ratio, the fraction of the
warned counties for which there is no tornado.

Year POD FAR
1986 0.338 0.813
1987 0.289 0.813
1988 0.290 0.813
1989 0.358 0.801
1990 0.438 0.715
1991 0.412 0.760
1992 0.453 0.695
1993 0.429 0.730
1994 0.459 0.743
1995 0.599 0.748
1996 0.593 0.770
1997 0.588 0.775
1998 0.652 0.802
1999 0.702 0.720
2000 0.648 0.762
2001 0.692 0.712
2002 0.757 0.750
2003 0.792 0.748
2004 0.759 0.743

If we limit attention to the strongest tornadoes (F2 or greater, roughly
10% of the tornadoes), the POD is a little over 0.8 for 2003 and 2004.

Maybe the forecasters suffer from the same problem as folk who assert
they will list data from 1986-1994, then quote twice as much. ;-)

Cheers, Phred.

--
LID