Here's a very basic explanation of reading a sounding, until I get time to work on it more. Head to the link above after entering the user id: bomw0007 and the password: aviation. Click on a town or area to get the sounding and follow the red line on the right of the chart (the one on the left is the DP) up to various pressure areas that are indicated on the left hand side of the chart. Below are some good temperatures to use as a guide for winter cold outbreaks. Typically, the better snowfalls come from systems with these temperatures or better as aggressive cold air convection will develop if surface patterns are favourable, ie: a low or trough is nearby. Make sure you have the latest sounding, so check the time stamp on the chart. I will add more as I have time.
850hPa level = -1C is okay for snow at 1100M ASL (especially under convection cells) but -2C or better is preferred. Even for the ski fields, -1C or better is preferred for snow that is not too wet and heavy.
700hPa level = -8C is okay but -10C is preferred.
500hPa level = -26C but -28C to -30C is better.
Remember, the temperature of an air mass in the lower levels can be colder than the actual soundings if cold air convection cells are occuring as mixing will occur. Orographic lifting over ranges can also lower the temp at 850hPa as the air will cool abiabatically which cools the air faster than the usual environmental rate.