Overnight the 1000 mile wide North Pacific High has pushed a huge ridge of high-pressure inland which is morphing into a separate high-pressure over the southern Great Basin/Four Corners.
This tends to turn our ocean winds a less favorable NNW direction and create NE winds over the
interior at the surface and just aloft.
This causes 2 problems:
1. The NE wind battles with the
inbound favorable NW-WNW winds making those winds later, weaker and less reliable.
2. Having northerly winds aloft helps a counter-clockwise AM eddy form off Southern California that also may block the inbound favorable winds