I agree with Jagat.  More ...

I agree with Jagat.  More stations will generate a better value. Take care to examine the location and physiography of the stations you use. Microclimatology demonstrates that small changes in distance can create large changes in precipitation. Using the daily precipitation from Station A and any other stations for which you have data, determine the percentage of the monthly precipitation for each day and apply that to the monthly precipitation at Station B.