Large-scale weather forecasts are made using sophisticated computer programmes that model a virtual world. The accuracy of the output of such a model depends on the quality of the input.

One of the usual sources of input is an aircraft, feeding back real-time wind data.

The coronavirus pandemic has considerably reduced the number of aircraft operating. As a result, the incoming information has dropped and forecast winds at cruise height can no longer be verified and the feedback loop into the global model is much weaker.

According to the European Centre for Medium Range Weather Forecasts (ECMWF), “Aircraft reports are second only to satellite data in their impact on forecasts. Between March 3 and 23, there was a reduction of 65 percent in reports received. Globally, the reduction was about 42 percent.”

There is a measurable reduction in the accuracy of forecasts winds, at aircraft cruise height, if all aircraft reports are removed. There is a smaller, but still statistically significant, impact on near-surface fields, up to 3 percent on surface pressure.

Mitigating the impact

Other types of observations are likely to be less affected by the disruption than aircraft reports, and there may be some additional radiosonde (balloon) launches to try to mitigate the lack of aircraft data.

Satellite data provides a lot of information on temperature and humidity fields, but less on wind fields.

A major tornado season in the US is coming up and in June the hurricane and typhoon season starts. While the effect, if any, on the forecast of these significant weather events is yet to be seen, hurricanes and typhoons are steered by winds in the middle and upper atmosphere so inaccuracy in these forecasts may prove to be significant.