number of consecutive lengths in a month of all year

hi
i have daily rainfall data in excel (column A=year, B=month, C=rainfall amount in mm).
i want to calculate number of times the rainfall value is consecutively zero, that is if the value is zero for consecutively 2 or 3 days they should be considered as one, and and number of consecutive times values are zero to be calculated monthly wise (all the year January month .......)
please help me i have attached the data file also.