Here are various sources for weather at Del Mar Thoroughbred Club just north of San Diego, CA. You may wish to check several and try to come to a consensus as to just what the weather will be like, but unlike other regular Breeders' Cup venues, the weather here is quite consistent.
Average high temperature on November 3 is 71 degrees with an average low of 57, while the record high is 93 degrees in 2010. The average rainfall for November is 1.17 inches, so there is a slight chance of wet weather. Late December through February is the most rainy time of the year there, so hopefully it won't rain in early November. The main track returned to dirt in 2015 after a few years as PolyTrack. Del Mar's turf course was also redone and made wider in 2014 after a series of breakdowns on the old surface. The new one, which uses GN1 Bermuda grass, has been much safer.
So when checking forecasts or current conditions on your own, look up the weather in Del Mar rather than at San Diego, as the track is about 20 miles north of the airport.
Review: Crushing the Cup 2016 - by Jim Mazur and Peter Mallett. An invaluable tool for trying to unlock the mysteries of handicapping the Breeders' Cup races. Updated for 2016, this is their 25th anniversary edition and they will have a new edition for 2017.
The Breeders' Cup Championship Day - The official page for the Breeders' Cup championship races. Just about anything you need to know about it: results, video clips, and race calls for past years, and eventually nominations, entries, and results.
Free Prep Replays - for major prep races in the Breeders' Cup Challenge. The ones with camera logos have video available.
Breeders' Cup Supplemental Entries - The old official policy on supplemental entries plus all the supplemental entries and how they fared, mostly it was a losing proposition. There are no more supplements now, only late nominations making it impossible to track since the change.