[Reading Science] As Winter Changes, Forecasts Must Change Too

The Era When "How Many More Days Will It Be Cold?" Matters Most

This winter's cold wave has left more than just frigid temperatures. Another major inconvenience felt by many citizens was the difficulty in getting a clear answer to the question, "How long will it stay cold?" Cold wave advisories were lifted and then reissued, and the timing of temperature recovery was pushed back with each forecast. The impression left is not simply of a cold winter, but of a season in which the forecasts themselves have become increasingly uncertain.

As temperatures dropped sharply and severe cold below freezing swept through, pedestrians hurried their steps passing through Gwanghwamun Square in Jongno-gu, Seoul recently. Photo by Dongju Yoon

This phenomenon is no coincidence. Meteorological experts point out that the nature of winter cold waves has changed recently, placing the existing forecasting system at a structural turning point. In the past, when cold air would quickly move in and then retreat, relatively stable predictions were possible. However, with the emergence of "persistent" cold waves that linger over specific regions, even a minor variable can alter the entire development of the situation.

Stationary Atmosphere Shakes Up Forecasts

Traditional weather forecasting has developed on the premise that atmospheric flows are mobile. The more regular the movement of cold air coming and going, the higher the accuracy of numerical forecast models. However, recent winter atmospheres are increasingly undermining this assumption. As jet streams slow and upper atmospheric flows become stagnant, cold waves are turning from moving events into stationary states.

Myeongin Lee, Professor at the Department of Urban and Environmental Engineering at Ulsan National Institute of Science and Technology (UNIST), explains, "When atmospheric flows are fast, even if there is a forecasting error, the outcome does not change much. But as the flow slows, small differences accumulate, and predictive uncertainty rises sharply." He points out that predicting the end of a cold wave has become the most challenging task.

In recent winter forecasts, the most frequently changing factor is not "how cold will it get," but "how long will it last." When the upper atmosphere's cold air-trapping flow becomes stationary, it is difficult to predict precisely when this structure will break down. As a result, forecasts alternate between predictions of prolonged cold waves and early lifting advisories, making it feel as though the forecasts are constantly changing.

Seungbae Kim, Head of the Korea Natural Disaster Association (and former spokesperson for the Korea Meteorological Administration), explains, "In recent winters, it is much harder to talk about the end of a cold wave than its onset," adding, "The reason forecasts feel like they change so often is because the atmospheric flow itself has slowed down."

From Numerical Forecasts to 'Lifestyle Forecasts'

Experts believe that, in light of these changes, the role of forecasts must also evolve. Simply stating a number, such as "minus several degrees," is not enough to convey the risks citizens actually experience. They advise that forecasts should shift toward communicating the real-life impacts, such as the risk of icy road accidents, surging energy demand, or health risks for vulnerable groups.

Even at the same minus 8 degrees Celsius, a one-day cold snap and a cold spell lasting more than three days have completely different consequences. If days go by without temperatures rising even during daylight hours, the risks of road icing or frozen water pipes increase sharply, and the danger of hypothermia for elderly people living alone or those with chronic illnesses also rises. The length of the cold wave, rather than its intensity, has become the key factor in determining risk.

Overseas, this perspective is already being reflected in forecasts. In some regions of the United States, cold wave advisories are accompanied by practical information, such as the likelihood of car ignition failures or recommended time frames for suspending outdoor work. In some European countries, when a prolonged cold wave is expected, forecasts are expanded to include advance warnings about peak electricity usage times or the need to protect vulnerable groups.

Experts suggest that Korea, too, should adapt its forecasts to the recurring pattern of persistent cold waves, expanding their role from "information explaining the weather" to "signals for adjusting daily life." Rather than focusing solely on predicting the coldest point, it may become more important for cold wave forecasts to inform the public about how long they need to remain prepared.