"It's going to be much colder and the showers will become persistent. It will be unsettled and definitely much, much cooler with a polar blast," he said.
However, there will be the odd bright periods as the sun tries to make an appearance through the winter cloud, he said.
Temperatures should reach 9C on Thursday and drop to 8C Friday.
And the weekend doesn't look like it will be any warmer or less wet.
"It's going to be unsettled for most of the weekend with the odd showers hanging around ... overall we're in for a week of unsettled weather ... [this] cold snap is a reminder that we're approaching the middle of winter."
As for next week, expect a bit of the same.
For more information go to www.metservice.com.