NMME ensemble for Dec. 2012 initial conditions contains 79 members, all weighted equally.
A/B/N [Above/Below/Neutral] are terciles.
* A and B contours show when one class has >38% of ensemble members, and the opposite class is below 33%.
* In the case that A is >38% and N is >33%, A will be shown. This is the same for B.
* N contours show when >38% of ensemble members fall in the “Neutral” tercile, and both A and B are below 33%.
* White areas show where no one class is dominant: either all terciles are under 38%, or both A and B are over 38%.
The tercile limits were determined separately for each model using the NMME hindcasts (1982-2010 ). For tmp2m and sst, the mean and standard deviation were found for each model and terciles set as mean +/- 0.43sd. For precipitation, thresholds were determined by ranking all hindcasts and taking the 66th and 33rd percentiles. Then, the number of ensemble members in each model that fell into the separate categories (relative to their own distributions) were tallied up.