If the allied have to send fighters and bombers into Syria, do you think that the Syrian air force could be threat?
http://en.wikipedia.org/wiki/Syrian_Air_Force
and not to forget their air defense
http://en.wikipedia.org/wiki/Syrian_Air_Defense_Force
Expect that most of the air defense and their air force may be heavy damaged after the tomahawk campaign.
But there after...
If I was Assad I would let the west bomb my old air force (MIG 21 and MIG 23) my modern air force I would hide very very deep under ground.
After this tomahawk campaign I would take every plane I have left from my old air force fleet and some of the new fighters load them with long range ASM(IF they have some) and AA-missiles
I'll do the same with my air defense. Activate it when the Allied fighters and bombers comes.
Markus