Trends in Japan

Meteorological Agency Refines Its Forecasts

APRIL 23, 1996

The Meteorological Agency dramatically upgraded its weather forecasts at the beginning of March, adding detailed local reports for 20-kilometer-by-20-kilometer areas and reducing the basic unit of time in the monthly temperature forecasts from 10 days to a week. Because climate has a widespread influence over everything from everyday life to business and commercial activities, the new system got off to an extremely good start with extensive public interest and acclaim.

Local Forecasts
The refinements were made possible by the switch to a supercomputer capable of processing information 10 times faster than its predecessor, which the agency had used for nine years.

The highlight of the new system is the addition of 24-hour local forecasts covering 20-kilometer-square areas. Formerly, weather reports were issued only for 130 places representing parts of or whole prefectures and measuring about 75-kilometers square. Now, however, reports are also made for the 2,000-odd blocks into which the country is divided and the 24-hour predictions are broken down into eight 3-hour segments. Information is displayed on maps subdivided by a grid whose segments correspond to these blocks. A series of maps are issued for each 24-hour report, with each one carrying forecasts on either the type of weather, precipitation, or temperature over a single three-hour period.

Tokyo Prefecture, for example, now covers eight blocks rather than a single unit (when the outlying islands are excluded), and it is possible to tell at a glance what the weather will be like in each area.

Another feature of the system is chronological forecasting, with 24-hour predictions on the type of weather and temperature for 138 major locations displayed on graphs subdivided into three-hour segments. Changes in temperature are depicted on a line graph and variations in the type of weather are indicated with rain, sun, cloud, and other such marks. It is now possible to discern during which of the three-hour intervals the temperature will drop or rise or the weather will change, a vast improvement over previous forecasts, which only revealed that, for example, it would become cloudy later in the day.

Forecasts are made available three times a day, at 5:00 a.m., 11:00 a.m., and 5:00 p.m., to press and disaster prevention agencies, private weather information firms, and other such organizations.

Probability Added to Monthly Forecasts
Sweeping changes have also been made to the monthly forecasts. Predictions of hours of sunshine have been added to the weather type, temperature, and precipitation forecasts, and temperature forecasts are now given in terms of weeks rather than 10-day periods. Moreover, vague pronouncements like "temperatures will be higher than average" have been replaced by such expressions of probability as "There is a 60% chance that temperatures will be higher than average."

The local coverage and precision of the Meteorological Agency's weather forecasts has some private weather information firms worried about staying in business. However, a number are confident they can compete by catering to the needs of communities, where detailed information on weather is essential when holding events and other activities.

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