Wow - I have heard of a poorer than normal raspberry crop this year but sounds like yours are really suffering. Dry soil and poor fertility is more likely the cause than winter weather. Raspberries appreciate a manure mulch in the spring and also need to have the old growth pruned back after they bear fruit. If your canes are older than 7 year you may need to start fresh especially if yellow leaves are showing signs of a viral infection. Does the foliage look healthy? Is the soil dry when you dig down three inches? Hope this helps, Keep growing, Marianne Binetti