Local conditions favor migration exodus. Just a few migrants are moving to our south and the precipitation in California isn’t going to help. You can look at the national composite and see this quite well. The low siting off the coast has slid a bit further south and is providing favorable southerly winds for migration in the PNW but is also bringing the precipitation to CA.
Nationally the picture is very clear. Looking at the 850mb wind plot we can see the three low pressure systems that are calling the shots. The one off the Pacific was discussed above.
The one in Canada above Minnesota is shutting down movement with strong NNW winds in the upper Plains states. But these winds do not reach much further south and we can see the migrants move in a narrow alley of access from Texas to as far north as the winds allow.
The last one is the one that has been slowing advancing across the country and has finally made it to the eastern seaboard and has brought precipitation that has grounded the birds.