SR/SSD 97-8 2-15-97

Last year was an exceptional one, in terms of QPF performance by meteorologists in the Forecast Operations Branch of the HPC. Verification records were set in eight out of nine categories for manually-produced 24-hour QPF. This success is in large part attributable to improved skill in the models. Here is a summary of threat scores:

Category	New Annual Record	Old Record/Year
Day 1	0.50"	0.387	0.351/1995
1.00"	0.271	0.265/1995
2.00"	0.170	0.169/1995
3.00"	0.131	0.095/1991
Update	0.50"	0.342	0.312/1995
1.00"	0.232	0.215/1995
2.00"	0.146	0.126/1995
Day 2	0.50"	0.304	0.283/1995

The only annual record that survived the performance of 1996 was the Day 2 1.00" category, with a threat score of 0.196, set in 1995. The 1996 threat score (0.193) was close to the record.

Monthly records were also set in six of the nine categories for the month of December 1996. Overall in the various categories, 41 new monthly records were set in 1996 (38% of the total possible).

As was the case for 24-hour QPFs, forecasters also set many record threat scores for 6-hour QPFs in 1996. Every previous annual record and 40% of the monthly records were broken. The issuance of 0-6 hour QPFs began in 1992, while 6-12 hour and 12-18 hour QPFs were begun in 1981. Here is a summary of new record threat scores:

Category	New Annual Record	Old Record/Year
0-6 hour	0.25"	0.330	1996	0.322	1995
0.50"	0.254	1996	0.253	1995
6-12 hour	0.25"	0.274	1996	0.261	1995
0.50"	0.197	1996	0.195	1995
12-18 hour	0.25"	0.239	1996	0.228	1995
0.50"	0.162	1996 (tie)	0.162	1995
0-6 hour	0.25"	0.439	Jan*	0.389	Jan 1995
0.404	Feb*	0.365	Feb 1994
0.363	Apr*	0.328	Apr 1995
0.315	Sep*	0.267	Sep 1993
0-6 hour	0.50"	0.356	Jan*	0.309	Jan 1995
0.291	Feb	0.276	Feb 1995
0.286	Apr*	0.252	Apr 1995
0.178	Jul*	0.132	Jul 1993
0.236	Sep*	0.201	Sep 1993
0.330	Dec*	0.296	Dec 1994
6-12 hour	0.25"	0.393	Jan	0.378	Jan 1987
0.346	Feb	0.326	Feb 1989
0.310	Apr*	0.273	Apr 1983
0.254	Sep	0.251	Sep 1988
0.353	Dec	0.350	Dec 1994
6-12 hour	0.50"	0.309	Jan*	0.266	Jan 1987/91
0.247	Feb	0.244	Feb 1989
0.120	Jul	0.118	Jul 1990
0.181	Sep	0.178	Sep 1988
0.275	Dec*	0.240	Dec 1988
12-18 hour	0.25"	0.347	Jan	0.328		Jan 1987
0.318	Feb*	0.287	Feb 1989
0.258	Apr*	0.232	Apr 1987
0.232	Sep	0.212	Sep 1989
0.323	Dec	0.318	Dec 1993
12-18 hour	0.50"	0.114	Jul*	0.089	Jul 1990
0.151	Sep	0.138	Sep 1988

An improvement of at least 10% over the previous record is marked with an asterisk (*)

Ed. Note: The threat score reflects how well the forecast matches the area which actually reaceived a given amout of precipitation. It accounts for size, shape, and location of the forecast, relative to what occurs. For example, imagine an isohyet which encloses the area where more than 2 inches of rain is forecast (call it area "F"). Now imagine an isohyet which shows where 2 inches or more actually fell ("O"). The threat score compares the area correctly forecast (the overlap of "F" and "O"--call it "X") with the area forecast AND observed ("F+O"). In other words:

If the forecast and observed areas overlap perfectly, then TS = 1, the maximum possible score. If they fail to overlap, TS = 0; there is no "credit" for a misplaced forecast, even if the shape and size of the area is the same as what is observed.