Contrary to what may be assumed, fallen meteorites are not hot; the heat caused by atmospheric friction abrades the outer layers, stripping away the heated portions, leaving the remaining portion as cold as they were while still in space. A free-falling meteorite spends less than thirty seconds in the atmosphere, which is not enough to heat it through. Touching a freshly-fallen meteor is more likely to cause frostbite than a burn.
The meteor trails clearly show that a number of them are following distinctly different trajectories. If, as it was stated, they all originated from the same comet or asteroid, all meteor trails would be parallel. Michelle mentions that the radiant is in Cassiopeia; this means that all the meteors would appear to be coming from that point in the sky traveling directly towards the observer, not following transverse paths.
It's stated that assistance is need from the Russians as "our satellites won't be in position, but theirs will". However, satellites don't remain in just one place, unless they are in geosynchronous orbit, when they'd be able to contact the ICBMs. In any case, there are sufficient US communications satellites around the Earth for several of them to be in a suitable position to contact the ICBMs. In addition, the Deep Space tracking Network makes use of major radio-telescopes around the Earth, of which at least one would always be in a position to contact something in space.
Element 120 has properties that can be predicted because of its position in the periodic table. Among those properties is paramagnetism, which means that it inly becomes magnetic with the application of an external electromagnetic field. Furthermore, since the force of magnetism decreases as the square of the distance from the magnet, the intensity of the magnetic field that would be able to attract meteors to the San Francisco area from space would be so strong that they could not have escaped detection before this time.
The explanation for the strikes concentrating on the San Francisco Bay area is that there is a mass of element 120 magnetically attracting the meteors. If the magnetic attraction were enough to pull chunks of iron out of space, it would draw them directly to the attracting mass rather than peppering the entire region.