Why does Israel get to keep its nuclear weapons?

[Seamus Fermanagh]

Given the wind patterns, wouldn't Japan and the US to a lesser extent get the worst fallout?

Too many variables to calculate properly. Yes, the prevailing winds do trend that direction -- a fact Japan used in its balloon bombing campaign in WW2 -- but precipitation, specific physical composition of ground zero for particulates, specific type of explosion, etc. would all factor into how much fallout, how dangerous, and how far it would spread.