Open the EPW file in your favorite text editor - one that doesn't wrap lines after a certain column. I use Ultraedit.
The top part of the file is header information. Copy the rows below that header information - starting at row 9 right to the bottom of the file. Copy that data into an Excel sheet, use Text to Columns with the delimiter set to comma. The 6th column is drybulb. Use an excel array formula to get the min and max for each month. On a second sheet, enter 1,2,3,4,.. for each month in a column. Then enter the min and max formulas beside the month number. In the example I just created:
{=MIN(IF(Sheet1!$C$3:$C$8762=Sheet2!$B4,Sheet1!$H$3:$H$8762))}. For array formulas, type the formula then use Ctrl-Shift-Enter to specify an array formula. Note, in my example, the weather data starts in Row 3, Column B - adjust the formulas depending on where you paste the data from the EPW file.
I don't know why some of the items get bolded in my answer.
Are you looking for a solution other than opening the weather file in excel or something and performing a statistical analysis there?
I think excel would work fine but how do I open the EPW in excel?