Weather Map Day

What Is Weather Map Day?

February 16 is "Weather Map Day" in Japan. On February 16, 1883, German meteorologist Erwin Knipping, who had been invited to the Tokyo Meteorological Observatory (the predecessor of today's Japan Meteorological Agency), created Japan's first weather map. Being able to see pressure patterns and wind flow on a map was a major step forward for modern weather forecasting in Japan. Note that this day was not established by the Japan Meteorological Agency.

Reading the Sky, Starting by Hand

The first weather maps were drawn from data on pressure, wind direction, wind speed, and more, sent by telegraph from 11 weather stations around the country, and were accompanied by a translated weather summary originally written in English. February 16 marks the day Japan began capturing its skies in the form of the isobars and high- and low-pressure symbols we now check casually on our smartphones.

From Daily Maps to Japan's First Forecast

From March 1 of that year, the weather map was printed and issued once a day, and from August 23 it was also posted at Shimbashi and Yokohama railway stations. It is said to have been printed in seven colors. The following year, on June 1, 1884, Japan's first weather forecast was issued: "Winds throughout the country are variable; the weather is changeable, but tending toward rain." It was posted at police boxes in Tokyo and elsewhere.

Weather Maps and Disaster Prevention

Weather maps are not just for knowing whether it will be sunny or rainy; they are also tools for protecting lives from typhoons, rapidly deepening lows, and other hazards. Modern weather observation, which began in the Meiji era, has evolved into precise forecasting using supercomputers and the Himawari weather satellites. February 16 is a day to appreciate these advances and to remember the importance of reading weather information properly.

Turning the Sky into a Map

The spacing of isobars and the shapes of fronts on a weather map make invisible air movements visible. On February 16, try looking at a weather map and imagining the vast movement of air overhead. Watching pressure patterns move from west to east reminds us that we live within nature's rhythms.

How to Read a Weather Map

• Isobars: Lines connecting points of equal pressure. The closer together they are, the stronger the wind.
• Highs and lows: Areas of higher or lower pressure than their surroundings, marked "高" and "低" on Japanese maps, with winds circulating clockwise or counterclockwise.
• Fronts (cold and warm): Boundaries between air masses of different character, where rain is likely and the weather changes.
• West-high, east-low: Japan's typical winter pressure pattern, bringing cold air and dry, clear weather on the Pacific side.
• Himawari's view: Comparing satellite images with weather maps gives a more three-dimensional picture of the weather.

Ideas for Enjoying Weather Map Day

• Look closely at today's weather map and try predicting how tomorrow's weather will change
• Search the JMA website for weather maps from past major typhoons or record snowfalls and compare them
• Enjoy the shapes of isobars as natural art
• Read books on the history of weather maps or columns by weather forecasters

A Forecast That Lights the Way

Weather Map Day is a day of challenge — the attempt to make the unknown future visible. Forecasts are sometimes wrong, yet people keep gathering data and drawing maps to protect lives and livelihoods. On February 16, look up at the sky, feel the chill or warmth in the air, and plan your day with accurate information.