how do i calculate snowfall per month?

I hope you can use some built-in packages, such as datetime, cause it’s useful when working with datetime objects.

import numpy as np
import datetime as dt

df = np.genfromtxt('test_files/COX_SNOW-1.csv', delimiter=',', skip_header=1, dtype=str)

date = np.array([dt.datetime.strptime(d, "%Y%m%d").month for d in df[:, 0]])
snow = df[:, 1].copy().astype(np.int32)

has_snowed = snow > 0

for month in range(1, 13):
    month_str = dt.datetime(year=1, month=month, day=1).strftime('%B')
    how_much_snow = len(snow[has_snowed & (date == month)])
    print(month_str, ':', how_much_snow)

I loaded the data as str so we guarantee we can parse the Date column as dates later on. That’s why we also need to explicitly convert the snow column to int32, otherwise the > comparison won’t work.

The output is as follows:

January : 13
February : 19
March : 20
April : 13
May : 8
June : 9
July : 2
August : 7
September : 9
October : 19
November : 16
December : 15

Let me know if this worked for you or if you have any further questions.