The culprit is what’s being called a monster Rex block weather pattern.
It’s made up of a high pressure system sandwiched between two low pressure systems. When one of the low pressure systems moves below the high pressure system, it blocks the high pressure. That means the system is stuck and will not be able to move for a long time.
Rex blocks are characterized by a high-pressure system located pole-ward of a low-pressure system. The Rex block will remain nearly stationary until one of the height centers changes intensity, unbalancing the high-over-low pattern, according to the National Weather Service (NWS).