Ausra already used real climatic data (although they arranged them randomly throughout the year) and found >90% correlation with the national load. If the plants are geographically dispersed then the problem of climatic extremes is reduced. But, it makes sense to be prepared for the worst.

Substantially more storage than 12-16 hours to deal with longer climatic irregularities is suboptimal from an economic viewpoint. If CST is to be the main supplier in the national grid, then it will make more sense to install emergence natural gas heaters (relatively cheap). A strategic natural gas reserve, and the existing natural gas networks could be used for this purpose. A month at full load would be more than enough to survive even the longest cloudy periods. In the future, biogas could be used with modest modifications on infrastructure. The quantity required is very low, just for the occasional emergence, not for regular operation, so this should be quite feasible.

Oh, and dealing with the winter load isn't that big a deal. An east-west axis orientation line focus plant, in a good location, has very consistent seasonal output. Most of the parabolic troughs built in the Mojave were north-south oriented to get a high summer bias, which is good for California, but if CST must provide a large chunk of the national generation then most plants would have to be in the east-west orientation.