Hi Etienne & All

You are near Dawson, I believe?  Checking Environment Canada website for the next week there, shows sunny days, clear nights starting tomorrow -20C/-34C warming to -4C/-17C by the weekend.  We seldom get down to -20C here, near Toronto, but when we do it is often with sunny days, near 0C followed by clear nights.  I blame the black coreplast slip-on covers I use for heating the hive during the day as you say which has resulted in hive deaths as I have said on Bee-L previously.
> 
> Just seeing hives going through extreme diurnal temperature swings caused by extra solar heating and then rapid cooling once the sun goes down just seems counter intuitive. 
> I use reflective bubble wrap for the opposite reason as my question above to prevent solar heating to keep the bees in a nice loose cluster vs heating them up during the day and then getting massive evening T plummets.

I agree with you about my sleeves providing wind protection and that they would be better if lighter in colour.  I have decided to move my last remaining sunny hives to my cedar bush site nearby instead of using the bubble wrap as you suggest.  The cedar bush hives with filtered sun all year have always produced as much or more honey than the sunny hives. 
All beekeeping is local, even a 100’ move can make a difference.

Bob Darrell
Caledon Ontario
Canada 44N80W
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