Offhand I cannot recall hearing about any forecasting method that can say with very much accuracy that an earthquake of some specific magnitude will occur at some location more than a few months into the future. Exact magnitudes would be especially difficult to determine. Fault zones can probably fracture in many different ways to produce earthquakes of different magnitudes.

Statistical programs might provide some information along those lines. But their probabilities would likely not be very high for specific times.

At the moment I would expect that it would be unlikely that the Los Angeles area would see a 6.4 magnitude earthquake in December of 2012. But that expectation is simply based on the fact that such high magnitude earthquakes don’t occur along the West Coast that often.