Coldest winter we've had here in well over 15 years. I know folks out west - like in MT/WY/KS, etc. - consistently get colder weather with more snow -but 'drier' winter conditions than we typically get here in the Southeast - but I also suspect that they aren't trying to overwinter cows on the same sort of (often poor quality) hay that a lot of folks in our area feed, often with no additional energy or protein supplementation.
For every degree below 18F, a dry(not wet) cow has to expend 1% more energy just to maintain body temp/condition. If they're not being provided with adequate calories, they lose body condition, and can 'starve to death' with belly full of (poor quality) hay. If they're wet, they burn through even more.
If dietary protein is deficient during the last trimester of pregnancy, colostrum quality & quantity can suffer - and calves born to those protein-deficient dams will have a hard time generating enough body heat to get on their feet, nurse, and absorb colostral antibodies. They may well freeze without getting up - and even if they do get up and nurse, those slow-starters may not get the colostral protection they need - and it will impact them throughout their growth period.
Additionally, birth weights are generally increased if temperatures have been COLD during the last trimester - and especially the last month - of pregnancy. I'm seeing that in the calves currently hitting the ground here; much bigger than has been the case in the past.
We moved to March calving from Jan/Feb a number of years ago, but are looking pretty hard at holding these 'spring' calvers over to a June calving season, and backing the Fall calvers up to June calving as soon we can - but that may take several years to accomplish.
Cold rain yesterday, changing over to freezing rain/sleet around 3pm, then to snow after dark. About 6" of snow on top of a sheet of ice. Cows were all festooned with icicles hanging off of them today - 'jingled' when they walked, and big balls of frozen ice/mud hung up in their tailswitches, whopping 'em as they walked.