Local weather is unpredictable, but we're talking about jetstreams here. They change gradually over more hours or days, so they're very predictable.

HKG->NYC can be flown many ways. The southern most is over Taiwan, skirting Japan, totally over the Pacific, south of the Aleutians, and enter around YVR/SEA. This also means paying Canada less or none at all for overflight rights.

Or it can still go past Japan, but then over Alaska, Yukon, and down through Canada.

Or if the tailwind is weak, they can fly north through China, eastern Russia into Alaska...

Or even use the Polar4 route though China, NE Russia, then into the Arctic Sea and down through Hudson Bay.

Or some combinations of above.

NYC->HKG is always north to North Pole, then usually Polar2 or Polar3 down through Russia, (Mongolia), China.