# MODEL QPF GUIDANCE VERIFICATION BY REGIONS

ADDED ECM FOR 24, 48, AND 72 HOURS; TEXT UPDATED DEC 1, 2008
ADDED SREF MEAN, REMOVED ODDS RATIO, POD, & FAR; TEXT UPDATED MAY 5, 2006
GRAPHICS UPDATED WEEKLY AS OF FEB 14, 2005
NEW REGIONS: TEXT AND REGION MAP UPDATED JAN 13, 2004
TEXT UPDATED MAR 19, 2003

This web site compares the performance of the NAM, SREF, and GFS for the prediction of 24-h accumulations of precipitation ending at 12 UTC. The European Center model (ECM) performance is included for projection hours 24, 48, and 72. The ECM forecasts are available to users in the U.S. later than comparable forecasts from NAM, SREF, and GFS.

The continental US has been broken into 14 regions in consideration of approximate uniformity of climatology and terrain. The verification was done on a 40-km grid. Graphical displays are generated for each region, each of six projection times (24, 36, 48, 60, 72, and 84 hours), and each of two time ranges (beginning one month and three months prior to the present). There are a total of 156 graphics to look at. A new set of graphics is generated every week.
Two measures of performance are displayed on each graph as a function of accumulation threshold. These measures are computed from the following traditional contingency table of event counts over a multitude of forecasts:

 Observed Not observed Forecast a  (hit) b  (false alarm) Not Forecast c  (miss) d  (correct rejection)
In the following discussion, N=a+b+c+d.  The computation of the performances measures displayed is described below:
1. Equitable Threat Score = the number of correct forecasts minus number expected by chance divided by the same quantity plus the number of erroneous forecasts = [a - (a+b)(a+c)/N] / [a + b + c - (a+b)(a+c)/N].  This score ranges from less than 0 to 1; a perfect score is 1.
2. Bias = the ratio of the total number forecast to the total number observed = (a+b) / (a+c).
In the graphs, the bias values are plotted along the axis on the right side of the plot.

# Click on a region name on the map below: 