Such crazy extremes are often related to the position and behavior of the jet stream. Whenever the jet flow pattern has multiple extreme dips and peaks, it signifies that unusual cold (U-shaped dips) or unusual warmth (U-shaped peaks) will result for the underlying regions.
Not only the jet, but local weather phenomenon, like sea breezes, can also play a role.
Weather whiplash is considered to be one of the biggest consequences of global warming and climate change. As Earth's average temperature warms, the amount of heat residing in the atmosphere increases. This means more frequent and intense heat waves (rising temperatures = hotter days), floods (warmer air holds more moisture which = heavier precipitation), drought and wildfires (rising temperatures = drier conditions), and storminess (increased heating of the air = increased convection).