and what causes those high pressure systems? atmospheric cooling.

there may be potential for something like this to push the jetstream in the east, where i am, down even further. the way that would work would be that the warm temperatures in the north pacific would keep the jetstream high up over alaska, thereby plunging it south through the middle of the continent. this would result in a warmer than usual fall in the west, and deep freezes in the east - along with serious late fall tornado activity in the plain states. so, it could be the kind of year here you get frost days in florida.

it would go away when the high pressure system lifts, and the imminent return of the sun would have to help.

https://www.theweathernetwork.com/ca/news/article/the-2019-blob-pacific-ocean-weather-patterns-autumn-fall