Japan’s weather agency to extend daily forecasts to two weeks

The Japan Meteorological Agency plans to make longer-term weather forecasts more detailed and accurate, to help people and businesses better prepare for extreme weather events that are becoming more frequent.

An expert panel convened by the agency recently compiled a report on improving weather forecasts, proposing that, with advances in climate data observations and simulations, it is possible and desirable to extend detailed forecasting from the current five days to two weeks.

The JMA’s daily forecasts include the day’s weather, high and low temperatures, chance of rain and the forecasts’ confidence levels.

The new report also proposed extending from five days to two weeks the period for which the agency provides information on the likelihood of warning-level heavy rain and snow.

The agency said it will aim to make the updates to forecasting operations — the first in three decades — by 2030.

“In recent years, extreme heat, heavy rain and heavy snow have caused damage across Japan on an almost annual basis,” the report said, citing as examples last year’s record number of ambulance calls for heatstroke cases and the record rainfall in Kumamoto Prefecture.

“Information covering periods from one week to several months ahead is taking on an increasingly important role as a form of ‘soft infrastructure’ supporting adaptation to climate change.”

Furthermore, the report proposed that, for monthly weather forecasts, the agency will provide temperature comparisons with more recent periods, such as the past three years.

Currently, the JMA indicates whether temperatures are expected to be “higher” or “lower” than the 30-year average.

With global warming, temperature forecasts are most often described as “higher than normal.” Such wording does not match people’s actual experiences or meet their needs, the report said.

The agency said the updates will not only help people better prepare for disasters and heatstroke but also aid businesses in planning and adjusting manufacturing and transport schedules as well as maintaining a stable power supply.