I have precipitation data ~20 years. For each year, I have the total precipitation for a given month for that specific year. I am trying to find if there there is a statistically significant difference between the years in the total precipitation. I have organized my data such that each column represents a specific year (i.e. 2000) with each column representing aspecific month (i.e. Jan). I am trying to do ONE way ANOVA using SPSS, however, the program is not giving me any results. Additionally, in the output data, the program is saying that it is unable to do post-hoc tests as "Post hoc tests are not performed for variable1 because at least one group has fewer than two cases".

I have a couple of questions about this:

Firstly, am I using the appropriate test (ANOVA) or should I be looking at an alternative statistic test?

Secondly, why am I am unable to get post-hot test results? Is the problem with the way I have organized my data OR is there a better way to preform the post-hoc tests?

Thanks in advance!!