I am using the following formula in cell H2 to calculate the minimum temperature (column C) each month. Column C shows every temperature observation taken at 3-hour intervals throughout the month specified in column B. In column H I am trying to calculate the minimum temperature each month from these observations. The formula works perfectly for 01/1981 (cell H2), but when copying the formula down the column it does not work, I just get a value of 0.

Here is a small sample:

Obs_Date    Obs_Date_short  Temp_C          Month   Month_short T_min   T_max
01/01/1981  01/1981 18.84           01/01/1981  01/1981 18.71   46.18
01/01/1981  01/1981 22.23           01/02/1981  02/1981 0.00    46.18
01/01/1981  01/1981 27.57           01/03/1981  03/1981 0.00    46.18
01/01/1981  01/1981 34.84                       
01/01/1981  01/1981 36.56                       
01/01/1981  01/1981 37.12                       
01/01/1981  01/1981 31.46                       
01/01/1981  01/1981 26.01                       
01/01/1981  01/1981 20.79                       
01/02/1981  02/1981 18.71                       
01/02/1981  02/1981 22.58                       
01/02/1981  02/1981 28.52                       
01/02/1981  02/1981 37.89                       
01/02/1981  02/1981 38.98                       
01/02/1981  02/1981 32.33                       
01/02/1981  02/1981 27.12                       
01/02/1981  02/1981 23.37                       
01/02/1981  02/1981 22.13                       
01/02/1981  02/1981 24.22                       
01/02/1981  02/1981 30.16                       
01/02/1981  02/1981 39.96                       
01/02/1981  02/1981 40.75                       
01/02/1981  02/1981 32.54                       
01/02/1981  02/1981 26.77                       
01/02/1981  02/1981 23.44                       
01/03/1981  03/1981 22.88                       
01/03/1981  03/1981 24.19                       
01/03/1981  03/1981 28.74                       
01/03/1981  03/1981 36.53                       
01/03/1981  03/1981 37.95                       
01/03/1981  03/1981 32.96                       
01/03/1981  03/1981 29.01                       
01/03/1981  03/1981 26.10                       
01/03/1981  03/1981 24.99                       
01/03/1981  03/1981 25.80                       
01/03/1981  03/1981 29.51                       
01/03/1981  03/1981 36.15                       
01/03/1981  03/1981 37.10                       
01/03/1981  03/1981 32.40                       
01/03/1981  03/1981 28.62                       
01/03/1981  03/1981 25.79                       
01/03/1981  03/1981 24.38                       
01/03/1981  03/1981 23.86                       
01/03/1981  03/1981 27.93                       
01/03/1981  03/1981 36.58                       
01/03/1981  03/1981 37.43                       
01/03/1981  03/1981 30.46                       
01/03/1981  03/1981 25.93