So long, fake spring. Winter weather returns to the Puget Sound area this week.

In Seattle, it’s an annual tradition to be tricked by what’s known as “fake spring.”

It’s when the sun — which hasn’t been seen since fall — suddenly reemerges in February or March, and we experience a brief yet pleasant reprieve from the cold, wet, dark of winter. People often see this unexpected shot of balmy weather as a sign that winter is over, but it’s not. That’s fake spring.

And now, fake spring is over. Following a week of dry, warm weather and sunny skies, lows throughout the region are expected to drop into the 20s this week. Steve Reedy, a meteorologist with the National Weather Service in Seattle, said the cold spell is coming down to the Puget Sound from Canada.

“Behind this front, we’ll have an upper-level trough that really deepens over the area,” he said. “That’s going to drag in some cold Canadian air for us, which will trigger those lower temperatures.”

To understand this better, Reedy said to imagine a pot of water with a rubber base. The pot is the trough that’s sitting over the region, and the water is the cold air. If you pull that rubber base down — deepening the trough, so to speak — the water sinks lower in the pot. That deepening trough is what’s causing the cold air to flood the region, Reedy said.

Reedy said temperatures will remain in the mid-to-high 20s overnight and in the early morning, and expects to see afternoon highs in the 30s. That will last until about Thursday, he said, when lows will warm slightly into the low-to-mid 30s.

The weather service expects light rain Monday, which could turn into a rain-snow mix as the day goes on. No accumulation is expected. Tuesday should be dry, but meteorologists say there’s a slight chance for rain Wednesday and Thursday.

Reedy said the warm, dry weather — the fake spring — the region saw was the result of a high-pressure system. The pressure settles over the area and acts like a bulwark that keeps wetter systems from entering the region. That high-pressure system has moved on, Reedy said, which is why we’re expected to see wetter weather and colder temperatures this week.