If bellwethers are your thing, this is a good write-up about the Washington state primary.

https://split-ticket.org/2024/08/22/a-very-detailed-examination-of-the-washington-primary/

Washington uses a top two primary where Republicans and Democrats face each other.

People have used it to predict how the country will vote in the general election. This year it indicates a D+3 environment.

That's pretty close to how the generic ballot polling has been. Generic ballot polling is currently D+~2.3.

If this is accurate, it points to Democrats as slight favorites to retake the House.