Hairy question - transpose columns

Hello;
I've got pluviometric data in a bizarre format (spanish administration is rather original) and I need to "transpose" them, to be able to use them as time series data for a model.
The original data are in a format like

cod_var | Year | Month | Ten | RainDay1 | RainDay2 | RainDay3 | Rainday4 | Rainday5 | RainDay6 | RainDay7 | RainDay8 | Rainday9 | Rainday10 | Rainday11
--------------+-----------+------------+---------+----------------+----------------+----------------+----------------+----------------+----------------+----------------+----------------+----------------+----------------+----------------+
452 | 1995 | 1 | 1 | 2 | 5 | 6 | -3 | 0 | 5 | 4 | 5 | 4 | 4 |
452 | 1995 | 3 | 2 | 4 | 5 | 0 | 5 | 3 | 23 | 4 | 34 | 4 | 2 |
452 | 1996 | 12 | 3 | 12 | 2 | 3 | 4 | 7 | 3 | 3 | 15 | 2 | 4 | 3
452 | 1998 | 9 | 2 | 2 | 8 | 6 | -3 | 5 | 0 | 2 | 6 | 0 | 1 |
452 | 1998 | 3 | 3 | 2 | -3 | 7 | 9 | 4 | 2 | 5 | 6 | 1 | 16 | 3
......................

As you may see, the date of a rain datum is defined by the value of the fields Year, Month,Ten (1=first ten days of month; 2=second ten days of month; 3=up to eleven last days of month).
and the field in which the datum is (RainDay1, RainDay2...)

This is no useful for me because I need something like:

cod_var | Year | Month | Day | Rain |
--------------+-----------+------------+---------+----------------+--
452 | 1995 | 1 | 1 | 2 |
452 | 1995 | 1 | 2 | 5 |
452 | 1995 | 1 | 3 | 6 |
452 | 1995 | 1 | 4 | -3 |
452 | 1995 | 1 | 5 | 0 |
452 | 1995 | 1 | 6 | 5 |
...................

Perhaps this is not possible to do with a database? Should I manage to make a program to fix this?

Thanks for your help. I really can't imagine how to do this with Postresql; though I'm a newbye.

Regards
-----------
Javier