John,

If I use the SKEW function I get the following values:

Period Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1659-2009 (0.6) (0.5) (0.1) (0.1) 0.1 0.2 0.4 0.3 0.0 (0.1) 0.0
(0.2)
1971-2009 (0.8) (0.8) (0.2) 0.2 (0.1) (0.2) 0.8 0.4 (0.1) 0.0
(0.1) (0.8)

Now what do I do with the value and the Standard Deviation?

If I have a December mean for the period 1659-2009 of +4.1c, and the
STDEV is 1.7c, and the SKEW is -0.2c, do I get a revised STDEV of 1.5c
or 1.9c? Then do I use +4.1c and the revised STDEV x1 x2 x3 etc to
get the revised Standard Deviation thresholds?

Your help is much appreciated.

Thanks