^{2} Under these conditions, the m categories yi are said to be
**mutually exclusive** and **exhaustive**.

^{3} A thunderstorm's probability is conditioned by the simultaneous
presence of moisture, instability, and lift.

^{4} There are other viewpoints. This will be explained as we
consider verification.

^{5} This leads to the question of how to interpret the values inside
the contours. It is possible to assume that all the pseudo-points that are
touched by the contour have the value assigned to the contour, but what about
in between contours. One possibility is to interpolate values to all the
interior pseudo-points. Another is to assign the contour value to everything
inside a given contour up to the next interior contour. The latter means that
only a limited set of probability values are allowed. Yet another
interpretation is that probabilities are binned, such that everything inside
one contour and exterior to another falls in a particular assigned bin range.
The choice among these and any other possible interpretations is somewhat
arbitrary and depends on the verification being done.

^{6} That is, it contains the totals for the *ensemble* of
forecasts, which might cover many days and many forecast periods. To examine
the time-dependendent information, you must reconsider the individual forecasts.