Here in Newfoundland we say it's not cold that kills bees it's moisture.  My winter apiary is on the Bonavista Peninsula on the east coast of the Island.  Our winters are very long with cold, often wet weather persisting sometimes to the middle of June.  Temperatures routinely fluctuate back and forth around 0 deg. C with rain, drizzle, and fog (on top of snow). I have been overwintering 12-14 colonies for 10 years. Myself and most of the other beekeepers in my orbit maintain upper and lower entrances with the lower at 7" wide. Some of us use shrew guards made from  1/4" hardware cloth (mesh wire).   I run all of my hives as "warm configuration" but I'm in a minority.  In the previous nine years, I have never suffered a single dead-out.  I've had other losses (e.g., drone laying queens), but never a winter loss. Fingers crossed for this year.  

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