Home > National > Environment

Meterologists use '600 degrees rule' to predict when cherry blossoms will bloom

Published: 16 Mar. 2026, 19:43 Updated: 16 Mar. 2026, 20:17

A bird gathers nectar from plum blossoms at a park in Daejeon on March 16. [NEWS1]

Cherry blossoms are expected to begin blooming in parts of Jeju on Sunday as daytime temperatures across Korea rise to between 11 and 18 degrees Celsius (52 to 64 degrees Fahrenheit) in the coming days.

Attention is also turning to whether the “600 degrees rule,” a widely used method for predicting cherry blossom blooms, will be accurate this year.

Meteorologists often use the 600 degrees rule — which accumulates the daily maximum temperatures every day from Feb. 1 — to estimate the timing of cherry blossoms’ bloom, which typically begin flowering once the cumulative temperature approaches 600 degrees Celsius.

According to the Korea National Arboretum’s cherry blossom bloom forecast released on Monday, more than 50 percent of the cherry trees at Halla Arboretum in Jeju are expected to bloom this Sunday. In the Aewol Gotjawal region in Jeju — including Nokkome Oreum and the Nam-eup warm-temperate forest zone — the blossoms are expected to be half-bloomed by March 27. At the 1100 Highland Road area of Mount Halla, where temperatures are lower because of the higher elevation, about half of the blossoms are expected to bloom on April 1.

The timing of the bloom in each location can vary depending on sunlight exposure and rainfall. The private weather service Weatheri previously predicted bloom dates of March 25 in Seogwipo, March 26 in Daegu and Pohang, March 27 in Gwangju, March 28 in Jeonju, March 31 in Cheongju, April 1 in Gangneung, April 3 in Seoul and April 8 in Chuncheon. In some parts of Busan, however, blossoms began to bloom on Sunday, more than 10 days earlier than the originally forecast March 25.

Cherry blossoms are in full bloom at a traditional house in Gangneung, Gangwon, on April 24, 2025. [YONHAP]

According to the Korea Meteorological Administration (KMA), the sum of daily maximum temperatures in Seoul from Feb. 1 to March 16 reached 390.8 degrees Celsius, meaning an additional 209.2 degrees is needed to reach the 600 degrees threshold.

If the daily maximum temperature averages 11.6 degrees Celsius, the cumulative temperature would reach 600 degrees before April 3, the expected bloom date for Seoul. The KMA forecasts that maximum temperatures in Seoul will range between 12 and 15 degrees Celsius from Monday to 26, and nationwide highs are expected to range between 11 and 18 degrees Celsius.

Cherry blossoms bloom in Busan on March 9. [YONHAP]

However, the 600-degree rule is not always accurate, particularly if warm weather is not sustained. Weathernews, Japan’s largest private weather service, reported on March 6 that the rule had not applied in 2024. Tokyo’s standard cherry tree bloomed 11 days after the accumulated temperature surpassed 600 degrees.

Japanese meteorological experts believe the delay occurred in 2024 because unusually warm weather in mid-February pushed accumulated temperatures quickly past the threshold, but an unexpected cold spell in March slowed the final development of flower buds.

In Busan, where cherry blossoms began blooming on Sunday, the accumulated temperature was only 523.4 degrees Celsius, also falling short of the 600 degrees benchmark.

Visitors enjoy spring in South Jeolla on March 15. [YONHAP]

Workers plant various spring flowers along a roadside flower bed in Busan on March 16. [YONHAP]

Meanwhile, people planning outdoor activities are advised to watch out for fine dust levels.

According to the Korea Environment Corporation, fine dust and ultrafine dust levels will reach “bad” levels in most regions on Monday and Tuesday due to domestic pollution and overseas dust blowing clockwise toward the Korean Peninsula. Ultrafine dust levels are also expected to remain “bad” in the Seoul metropolitan area, the Yeongseo region of Gangwon and the Chungcheong region on Thursday.

The Ministry of Climate, Energy and Environment issued a “concern” level ultrafine dust alert for the Seoul metropolitan area and South Chungcheong as of 5 p.m. on Monday. Emergency reduction measures will be implemented from 6 a.m. to 9 p.m. on Tuesday. Under the measures, three coal-fired power units and waste incineration facilities in Incheon will adjust operating rates, and construction sites will be required to modify working hours.

“Concern,” the lowest level in Korea’s four-tier pollution alert system, signals that high fine dust levels are expected and that response measures may be implemented.

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.
BY HEO JEONG-WON [[email protected]]