The program ONLINE_THORHTHWAITE calculates potential evapotranspiration (PET) by the Thornthwaite method.

1. The input is:   (a) the chosen month, (b) twelve (12) values of mean monthly temperature T_i (^oC), (c) latitude (degrees), and (d) hemisphere (either North or South).

2. The output is:   Monthly PET (cm).

3. Monthly potential evapotranspiration (PET) is a function of:   (a) the series of mean monthly temperatures, (b) the mean monthly temperature for the given month, (c) latitude, in degrees, and (d) hemisphere, either North or South.

4. Mean monthly temperature is restricted to nonnegative values (^oC). It is recommended that if a value of mean monthly temperature is less than 0 ^oC, it should be taken as 0.

5. Input allowable ranges: (a) latitude North, 0-60 degrees; and (b) latitude South, 0-50 degrees. Input data outside of these ranges will trigger error messages and stop execution.