UTM Zone numbers in utm python library

[micah-prime]

The way we use UTM zone numbers is not consistent with the utm python library. 'N' corresponds to a different zone than just North, so a better way would be to not use a zone letter and just set 'northern=True' in the "to_latlon" function.

https://github.com/Turbo87/utm/blob/master/utm/conversion.py

This is not currently breaking anything as the utm code just checks if the value is >= 'N' to see if it is north or not. We're getting by unharmed, but this should be updated.

Setting northern=True should work great in this code assuming we do not want to model south of the equator, which we can't do with the HRRR dataset anyway.