Temperatures dropped sharply across the country over the weekend as cold wave alerts were issued for most regions.

The Korea Meteorological Administration said Sunday’s morning lows dropped below 5 degrees Celsius nationwide with many regions marking the coldest weather of the year.

Seoul saw its first ice of the year Sunday, a week earlier than the last year and 17 days earlier than the average, according to the KMA.

The capital city’s Sunday morning low recorded 1.3 degrees Celsius, the lowest for mid-October since 1957.

The mercury began to fall from Saturday afternoon as the first cold wave alert in October since 2010 was issued for Seoul.

A cold wave alert is issued when the lowest temperature is expected to fall 10 degrees or more to less than 3 degrees Celsius and record 3 degrees lower than the annual average. It can also be issued when the morning lows are forecast to be lower than minus 12 degrees Celsius for two days or longer.

The KMA can also issue a cold wave alert if severe damage is expected from the rapidly dropping temperatures.

For the reasons behind the early cold weather across the country, the agency explained that high pressure pushed a high-altitude patch of cold air from the northwest, and the air then fell across Korea.

“As the cold air flew into the peninsula fast, the temperatures dropped rapidly and the wind chills were 2 to 6 degrees lower than the actual mercury with strong winds,” the KMA said.

Although the cold wave alerts were lifted as of 10 a.m. Sunday, the KMA forecast that the unusual chilly weather will continue through Monday with strong winds. The agency added that temperatures are expected to gradually go up later in the week.

The KMA cautioned people to keep warm and pay attention to their health as a rapid drop in temperature can lead to weaker immunity.