From the New York Times: “An American official familiar with the military planning said that the initial target list has fewer than 50 sites, including air bases where Syria’s Russian-made attack helicopters are deployed.”
This is what a row of helicopters looks like at Mezzeh Military Airport, just west of Damascus, as seen on Google Maps.
It’s about two and a half miles from Bashir Assad’s palace:
A big explosion at the air base would be seen from the palace, which sits on a mountain, overlooking the city.
So while the target list isn’t set, those helicopters sure appear to be extremely likely targets for any incoming cruise missiles.