Red Flags will fly throughout the California today and into the weekend, ending on Saturday night. Why? Well, due to a "strong cold front entering Northern California tonight bringing very dry gusty winds." The mixture of said winds and low humidities, it seems, will "create critical fire conditions in the Northern California Valleys and Foothills" on Friday and Saturday.
A red flad warning means that fire conditions are "either occurring now or will shortly." All mountain regions, especially the Santa Cruz Mountains, should be on alert. So, you know, be careful out there, folks. Oh, and you can read more about the advisory here.