Heavy snow warnings were issued across the country as South Korea -- especially the Greater Seoul area and Gangwon Province -- experienced heavy snowfall nationwide, with more expected overnight.

According to the Korea Meteorological Administration, more than 20 centimeters of snow covered parts of Seoul as of 7 a.m., Wednesday morning.

Normally, a warning is issued by the KMA when snowfall is expected to reach above 20 cm within 24 hours. The last time a snowfall warning was issued by the KMA was Jan. 4, 2010, according to the KMA’s records.

Across its districts, Seoul received an average of 16.5 cm of snow, which also marked the highest November snowfall since 1907, when weather recordkeeping first began.

Besides Seoul, cities in the northern parts of Gyeonggi Province also saw heavy snow, with cities like Pocheon and Uijeongbu recording up to 14.6 cm and 13.7 cm of snow. Mountainous parts of Gangwon Province saw snow ranging between 10 to 20 cm.

As for the reason behind the unusually heavy snowfall in Seoul, the KMA stated that it could be attributed to the cutoff low pressure system situated north of the Korean Peninsula.

A cutoff low pressure system forms when a jet stream -- a band of strong winds in the upper atmosphere -- flows in a highly wavy pattern. As this type of low pressure system traps extremely cold air coming in from the Arctic, it destabilizes the atmosphere significantly.

“Snow clouds were formed as the cold air from the northwest moved past the West Sea, which is still relatively warm from the retained heat from Korea’s unusually warm summer and fall,” KMA official Woo Jin-kyu explained to The Korea Herald. “The contrast between the cold air and the warm sea waters resulted in the formation of snow clouds.”

With record-breaking snowfall and fast-dropping temperatures, traffic disruptions and accidents were reported throughout the day.

According to the Korea Airports Corporation, 40 flights were canceled and 180 flights were delayed due to the snow nationwide, as of 1 p.m. At Incheon International Airport, 75 flights, out of the 180, were delayed. Ninety-six passenger ferries on 74 routes were also halted nationwide, and entry to national parks, including Bukhansan and Seoraksan, was restricted.

As of 2 p.m., the Ministry of the Interior and Safety upgraded the operations of the Central Disaster and Safety Countermeasures Headquarters to Level 2 and raised the heavy snow warning from "caution" to "alert."

With ice building up on roads, the ministry also warned of traffic congestion during the morning and evening rush hours. At 6:40 a.m., five vehicles collided with one another due to heavy snowfall on the Seoul Yangyang Expressway, resulting in one death and six others sustaining severe injuries.

Seoul Metro Line No. 9 also experienced delays of up to nine minutes during the morning rush hour, causing overcrowding on subway platforms. Line Nos. 1 to 8 also experienced small delays, as a sudden surge of passengers on subway platforms made it difficult for platform doors to close. At Gunja Station on Line Nos. 5 and 7, platform doors malfunctioned due to moisture issues.

With heavy congestion expected during the morning and evening rush hours, the Seoul Metropolitan Government extended rush-hour operations from Wednesday morning. Subways will come at more frequent intervals, by 30 minutes on Lines 2 and 5 through 8, as well as for intra-city buses. The city government added that such extended hours will be maintained until Level 2 of the three-tier response system is lifted by the Interior Ministry.

Regarding the heavy snowfall nationwide, South Korean President Yoon Suk Yeol instructed the Interior Minister and the Transport Minister to "mobilize all available manpower and equipment for snow removal to prevent traffic accidents and congestion," according to the Presidential Office's written statement on Wednesday.

"As heavy snowfall is expected to continue until tomorrow morning, thorough measures must be taken to prevent further damage and inconvenience," added Yoon, calling for increased public transportation services during rush hour to minimize commuter disruption.

Heavy snow was expected to fall once again from Wednesday night to Thursday morning, reaching up to 15 cm in the Greater Seoul region and 20 cm for Gangwon Province. Other provinces, such as the Chungcheong provinces, Jeolla provinces, and Gyeongsang provinces, as well as Jeju Island, were expected to see snow of up to 10 to 15 cm. Morning temperatures were expected to reach as low as minus 5 degrees Celsius, while daytime temperatures were expected to range between 3 C to 12 C on Thursday.