In the two clauses, find out what the subjects are. In the first clause, its Alaska, in the second its temperature in Florida. Now you cannot compare apples to footballs , you compare apples to another fruit. What I mean to say is, compare like things. So either compare Alaska and Florida, or compare the temperature in Alaska to temperature in Florida.
So the sentence should be
Unlike Alaska, where the winter is .., Florida has a temperature that rarely goes below freezing point. (Not the perfect sentence but comparisons on point here).
Or
Unlike temperature in Alaska, words describing temperature in Alaska (not just Alaska) , the temperature in Florida rarely goes below freezing.
Hope this helps.
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