Ice storm and blizzard both list a 100% accuracy bonus, but that is misleading. The power that has the acc bonus is simply the power that summons the pseudo pet that deals the actual damage. For some reason, many pseudopet summoning powers list this 100% accuracy bonus. The pseudopet has a power that does the damage, and *that* power doesn't have any accuracy bonus.
For freezing rain/sleet, it doesn't really matter if you slot it with accuracy or not. It checks to hit 5 times per second, and you only need it to hit once for the debuffs to apply. For ice storm and blizzard, though, you want as many ticks to hit as possible, so you want some accuracy slotting in there. Personally, if you're slotting with SOs, I'd slot blizz/icestorm with 1 acc, 3 dam, 2 rech. Combined with sleet/FR, that should ensure a decent rate of hits. I wouldn't bother with any slow, though - if you're an cold/ice, you've already got slows coming out of your ears, you hardly need extra slotting for slow on attack powers.
@MuonNeutrino
Student, Gamer, Altaholic, and future Astronomer.
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If you plan to always use sleet in combination with the other rains, then you don't need accuracy slotting. If you want to use them on their own then two accuracy SOs are best.
thanks guys. I really appreciate it 
Another slotting considertion for Blizzard is to-hit debuffs. It has a base of -20% which is pretty high.
Level 50s: to many to remember at this point
I was looking at the Acc values for ice storm/blizzard/sleet and they all seem pretty high all on their own with no Acc slotting. Is there any reason to still slot them with Acc (maybe just 1?) or should I not bother and go for damage/recharge/slow?