This isn’t accurate, for a start.
The Mk-41 three stage Deuterium-tritium fusion bomb had a yield of 25 Megatons. Given the weight range, it could theoretically have gone even higher. (None of the large versions were ever fired, so the actual high limit is unknown.)
See http://nuclearweaponarchive.org/Usa/Weapons/Allbombs.html for a complete listing.
Exactly. To elaborate further, a chaotic system can and typically is fairly predictable in the short term, i.e. not very sensative at all to the initial conditions, yet will be VERY sensitive in the long term. It is not just that parmeters are not measured closely enough to determine the ultimate outcome, and someday we could make accurate enough measurements, the idea is that there is NO finite resolution that is adequate.
Weather pretty much exactly fits this discription. Short term forcasts can be fairly accurate, but nobody seriously even tries predicting the weather on March 3 two years from now. (OK, theres “Ye Olde Farmers Almanac”) If you looked at the predicted track of Katrina, there was a huge error band at just 12 hours out.