Data frame with components:
Year: integer years from 1900 to 1999,
Mn: integer months from 1 to 12,
Dy: integer days of the month (i.e., from 1 to 28, 29, 30 or 31 depending on the month/year),
MxT: integer valued daily maximum temperature (degrees Fahrenheit),
MnT: integer valued daily minimum temperature (degrees Fahrenheit),
Prec: numeric giving the daily accumulated precipitation (inches),
Snow: numeric daily accumulated snow amount,
SnCv: numeric daily snow cover amount