(CNN) -- The recent snowstorm in China, which has stranded hundreds of thousands of people across the country and killed dozens, is related to the La Nina phenomenon, according to a Chinese weather expert



Suzhou, China, is blanketed by the most snow the city has had in 25 years, according to I-Reporter Susan Arthur.



La Nina is the opposite of El Nino, which follows El Nino and occurs every few years. During La Nina, sea temperatures over eastern equatorial Pacific are lower than normal.



La Nina enhances Arctic weather systems and causes a cold winter in Asia, including in China.



As warm and moisture air from the south meets cold air in the north under freezing temperatures, snow forms.



"The warm air is very active this year," said Li Weijing, deputy director-general of the National Climate Center of China.



As a result, persistent snowstorms occur in central and western China, paralyzing the transport and electricity systems.



The current storm, which hit just ahead of the Lunar New Year holiday -- China's busiest shopping season -- has shut much of the nation down. China's transportation system and power grid have been paralyzed this week.



The storm also has cost the nation's economy $4.5 billion, according to figures released Wednesday by the Civil Affairs Ministry.  Watch how Nanjing is coping with the unusual weather »



The winter precipitation had caused at least 49 deaths due to collapsed roofs and treacherous travel conditions, the Ministry of Civil Affairs and local officials said.



More than 177 million Chinese were expected to travel by train, and 22 million more by plane, for the February 7 Chinese Lunar New Year, also known as the Spring Festival.



China uses a color system for its snowstorm warning:



The current once-in-50-years snowstorm calls for the red warning, the first time such a warning has been issued since the system launches. E-mail to a friend



CNN's Clarence Fong contributed to this report.
Was anyone killed? what Li talked about? What did Li say about the warm air this year? what current snowstorm calls for? what amount of people have been stranded? What calls for the first-ever and most severe red warning?
dozens, "The warm air is very active this year," "The the red warning, hundreds of thousands once-in-50-years snowstorm
question: Was anyone killed?, answer: dozens, | question: what Li talked about?, answer: "The warm air is very active this year," | question: What did Li say about the warm air this year?, answer: "The | question: what current snowstorm calls for?, answer: the red warning, | question: what amount of people have been stranded?, answer: hundreds of thousands | question: What calls for the first-ever and most severe red warning?, answer: once-in-50-years snowstorm