The current combined offensive led by al Qaeda/Nusra on Aleppo is the beginning of the realization of the plan that started to be implemented some 11-12 months ago, which then became UN SC 2254 and the joint "US-Russian peace plan"

Few theses on the current state of the battle for Syria:
1. As I predicted several months ago (a well tried device used several times in Bosnia was applied again to Syria), the US imposed "ceasefire" supported by Russia (as of February 26) played a key role in ensuring the necessary preparations for the long planned Nusra-led offensive. Moreover, the US-Russian ostensible "peace plan" did set the deadline for the plan on August 1, which, as it turned out, was the beginning of the takfiri offensive on Aleppo. Without this "ceasefire," it would have been either much harder or even impossible to secure the preparation of the said offensive. In a word, such "ceasefires" are meant (as was the case in the past) to stop successful offensives against US proxies and to set the best possible conditions for the ceasefires' ensuing "violations" in the form of "sudden" offensives by the retrained and re-equipped US proxies. The ruse is rather simple, but it keeps working.
2. The odd and adventurous "march on Raqqa" was one of the key prerequisites for increasing the success of the long planned offensive of the Nusra-led current offensive on Aleppo.
3. Putin's withdrawal of most of the Russian Air Force group in Syria also ensured that Syria and Russia had a much smaller Air Force available in the theater of operations during this offensive.
4. It is possible that the well beforehand announced deployment of Russia's sole aircraft carrier off Syria in September was meant to take place "after the fact" so to speak--to serve a potential Russian evacuation from Syria.