Japan’s Tornado Warning System Sees Five - Fold Improvement

Japan’s tornado warning system sees five-fold improvementThe Japan Meteorological Agency says its new tornado prediction system is five times more accurate than its predecessor and enables some warnings to be issued up to 30 minutes earlier.
Tornado forecasting is a difficult science. In only a few percent of cases in Japan, powerful gusts of wind actually occurred in areas where tornado warnings had been issued.

The agency has improved the accuracy of its Hazardous Wind Watch using the latest scientific findings and high-performance radars. Operations of the new system started in December.

Warnings are issued by the agency when tornadoes, downbursts and other types of hazardous gusts of wind are predicted to likely occur in certain regions based on the condition of cumulonimbus clouds and other factors.

Between 2011 and 2014, around 600 tornado warnings were issued annually, but their accuracy rate was very low.

In 2014, tornadoes formed in areas where the agency had issued warnings in only 2 percent of cases. This ratio is known as the accuracy rate.

In addition, tornado warnings had been issued in advance only in 27 percent of cases where powerful gusts of wind were reported. That rate is known as the capturing ratio.

Forecasting tornadoes is difficult because they are “a small-scale phenomenon,” according to the agency’s forecast department.

As tornadoes form quickly and affect limited areas, the conventional radar with a resolution of 250 meters by 250 meters cannot precisely monitor vortexes of air that cause a tornado to start churning, agency officials said.

Referring to the results of its past surveys, the agency created a model of how a vortex forms that allows it to predict more accurately where tornadoes will likely occur based on a vast amount of data on temperature, humidity and other factors.

The agency also uses weather data from the land ministry’s high-performance radars to detect signs of tornadoes more easily.

To test the accuracy of the new tornado forecast system, data gathered between April 2012 and September 2014 was inputted into the system.

The results showed the accuracy rate improved from 3 percent to 14 percent under the new system, while the capturing ratio rose from 40 percent to 70 percent.