INterstate 5 now closed going into Santa Clarita northbound lanes. I realized this likely was going to happen earlier because of direction of the winds

 If you are heading north likely you will have to take 101 presently because Interstate 5 is now closed North bound. They likely are leaving the South bound lanes open at present just so people can get over the Grapevine down into the cities of Los Angeles safely. It makes sense in case the fire heads any further north and allows the fire engines to make a stand on the northbound lanes to start fighting the fire there.

As of 2:37pm pacific time they have also closed the Southbound lanes of Interstate 5 as well. So, now Interstate 5 is closed both directions at Santa Clarita so the main alternative to I-5 if you are heading north or south is 101 on the coast because there are few ways north and south (at least at this location).

I'm watching live local TV on this fire at:

https://www.nbclosangeles.com/news/california-wildfires/hughes-fire-castaic-la-wildfires/3612459/