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Why Is Japan’s Weather So Difficult to Forecast? ―How the Four Seasons and Topography Create Weather Complexity and Affect Businesses―

2025.05.30

Japan is situated on the eastern edge of the Asian continent, and its unique topographical features contribute to extremely volatile weather patterns. As a result, weather forecasting in Japan is considered among the most challenging in the world.

This article begins by explaining the distinctive features of Japan’s weather, then examines the question: “Can global models truly forecast Japan’s weather accurately?”—highlighting the strengths of the Japan Weather Association’s (JWA) forecasting models.
It also outlines the risks that Japan’s complex weather poses to businesses and introduces JWA’s solutions for mitigating those risks.

Key Points of This Article

  • Japan’s weather is heavily influenced by its complex topography and seasonal winds, resulting in highly volatile weather that makes forecasting particularly difficult.
  • Global weather models, such as those from ECMWF and NOAA, may have limitations in accurately forecasting Japan’s unique weather patterns.
  • JWA continuously hones its forecasting technologies to address Japan’s unique and diverse weather, offering solutions tailored to various industries based on its own highly accurate and reliable data.
  • Weather is a key factor that can pose both risks and opportunities for businesses. Leveraging accurate weather information tailored to local weather characteristics is essential for success in the Japanese market.

1. Is Japan’s Weather Difficult to Forecast? Characteristics of Seasonal Weather

Japan stretches from north to south, and its topography and climate vary greatly from Hokkaido in the north to Okinawa in the south.

The country experiences four distinct seasons, and during seasonal transitions, atmospheric fronts often cause unstable weather.
Moreover, Japan faces a wide range of weather events throughout the year, including the rainy season, typhoons, and heavy snowfall.

  • Spring (March- May): Changeable Weather with Pollen and Yellow Dust Impacts
    • Influenced by the westerlies, alternating high- and low-pressure systems pass over Japan, leading to significant weather changes every few days (four to five days).
    • In addition, during this season, cedar and cypress pollen is widespread, and yellow dust blown in from desert regions of the Asian continent further affects air quality.
  • Summer (June-August): Hot and Humid, with Rainy Season, Typhoons, and Localized Torrential Rains
    • The rainy season (Baiu or Tsuyu), which lasts for about a month and a half from around May to June, occurs due to the formation and stagnation of a stationary front called the Baiu front, caused by the collision between cold, dry northwesterly winds from the continent, which were dominant in winter, and warm, humid southeasterly winds from the ocean, which intensify toward summer.
    • Additionally, cool, moist northeasterly winds from the Sea of Okhotsk contribute to the prolonged rain and cloudy conditions during this period.
    • Once the rainy season ends, a Pacific high-pressure system settles over the Japanese archipelago, marking the onset of full-scale summer.
      Because this high-pressure system contains a large amount of water vapor, humidity levels across Japan become extremely high during summer.
    • Furthermore, the period from summer to autumn marks typhoon season in Japan.
      Of the typhoons that form in the northwestern Pacific or the South China Sea, around ten typhoons approach or make landfall in Japan each year.
    • Their paths are heavily influenced by upper-atmosphere airflows, and whether a typhoon approaches or makes landfall in Japan depends largely on the positioning of the westerlies and the Pacific High.
    • Additionally, because there are a lot of steep mountains in Japan, strong updrafts tend to form. As a result, especially in summer, intense localized downpours frequently occur over small areas in short periods.
    • This is a defining characteristic of Japan’s weather, and these topography features significantly increase the risk of landslides and related disasters.
  • Autumn (September, October, November): Cooler Weather with Latter Half of Typhoon Season
    • In autumn, Japan experiences alternating cycles of cloudy or rainy days and clear, sunny days.
    • Around September and October, a stationary front known as the Akisame (autumn rain) front appears.
    • This front typically lingers for four to five days and is gradually pushed southward by cold air masses from the north, eventually dissipating.
    • Autumn also marks the latter half of the typhoon season.
      During this time, the westerly winds strengthen; therefore, typhoons tend to move faster than those in summer.
    • Because warm, moist tropical air flows from a typhoon toward the front, their convergence can result in widespread heavy rainfall.
    • Additionally, localized torrential downpours, similar to those seen in summer, may still occur.
  • Winter (December, January, February): Heavy Snowfall on the Sea of Japan Side, Frequent Clear Skies on the Pacific Side
    • The region from Hokkaido to Hokuriku in Japan is known as one of the world’s snowiest areas.
    • During winter, Japan’s weather varies significantly by region: the Sea of Japan side typically experiences heavy snowfall, while the Pacific side tends to have many dry, sunny days.
    • Cold, dry air masses from the Siberian High (northwest monsoon) absorbs large amounts of water vapor from the relatively warm waters of the Sea of Japan.
    • This moisture-laden air brings heavy snowfall on the Sea of Japan coast. Conversely, as the air crosses the mountains toward the Pacific side, it loses much of its water vapor, resulting in prolonged clear skies and a dry climate with low humidity.
Map of Japan and surrounding areas
Map of Japan and surrounding areas

2. Can Global Models Truely Forecast Japan’s Weather?

Limitations of Global Models

Weather forecasts from global models—such as those provided by ECMWF or NOAA—may have limitations in accuracy for regions like Japan, where the topography and meteorological conditions are highly complex.

First, these global models have relatively coarse resolution, making it difficult to detect localized weather events in mountainous or urban areas. Moreover, their infrequent update cycles make it challenging to respond to rapid, short-term changes in weather.

Additionally, relying solely on the raw outputs of global models often results in reduced forecast accuracy—especially in mountainous regions and urban areas, where forecast errors tend to be more significant.
To enhance accuracy, it is essential to apply adjustments (guidance) that utilizes Japan’s high-density observational data.

Advantages of JWA’s Weather Model

Japan Weather Association (JWA)’s weather model provides high-resolution forecasts with a grid spacing of less than 1 km and updates every hour.

By leveraging Japan’s dense domestic observation networks—such as AMeDAS and XRAIN—JWA applies real-time corrections to significantly enhance forecast accuracy.

In addition, JWA incorporates AI-based correction technologies, enabling highly reliable and purpose-specific forecasts.
These include forecasts for temperature distribution, power generation, snow depth, and energy demand.

* For more information about JWA’s technology, click here: TECHNOLOGY

* For details about “JWA Blend of Models,” click here: JWA Blend of Models (only available in Japanese)

* For the 2024 accuracy verification results of JWA Blend of Models,” click here: 2024 Japan Weather Association’s Forecast Accuracy Verification Results

3. Business Risks Posed by Japan’s Weather and Solutions Provided by JWA

Power and Energy Industries

Logistics and Transportation Industries

  • Risks
    • Changes in delivery routes due to rainfall or snowfall
  • Example Solutions
    • GoStop Management System (only available in Japan)
      A web service that allows users to instantly view transportation impact risks caused by weather conditions on expressways, national highways, railways, and maritime transport including major ports and shipping routes across Japan.

Retail, Manufacturing, and Apparel Industries

  • Risks
    • Fluctuations in product sales and customer traffic due to weather conditions
  • Example Solutions
    • Analyze product sales and weather data to forecast product demand and customer traffic to adjust production volume and optimize inventory management.
      * For details about product demand forecasting, click here: Product Demand Forecasting

Other Services

In Japan, weather-related events that require forecasting and countermeasures occur cyclically throughout the year.
At JWA, we also provide various highly accurate services, including: Weather Data API

Overseas Support and Data

4. Conclusion: Turning Complex Weather Forecasts into Business Value

Although weather forecasting in Japan tends to be challenging, accurate forecasts are possible by leveraging JWA’s advanced data and weather models.

To succeed in business strategy within Japan, it is essential to utilize localized weather information tailored to the country’s unique topography and climate.

These highly accurate forecasts can directly contribute to cost reduction, risk mitigation, and the prevention of missed opportunities—ultimately enhancing business performance.

For inquiries, contact us.