Weather News

Coronavirus could make weather forecasts less accurate

Ben Domensino, Thursday March 26, 2020 - 12:02 EDT

The effects of COVID-19, widely referred to as Coronavirus, have been far reaching in recent months. Health systems have been overrun, economies are taking a beating and daily life has been disrupted for billions of people around the world. Now, data suggests that Coronavirus may be reducing the accuracy of weather forecasts as well.

Global efforts to slow the spread of Coronavirus have seen a significant reduction in domestic and international air-traffic in recent weeks. All Qantas and Jetstar international flights will be suspended from the end of March until at least the end of May.

While these travel bans are helping to curb the spread of the virus, they are also impacting the performance of weather models around the world.

Computer models are the backbone of modern weather forecasting. These 'numerical weather prediction' (NWP) models use powerful supercomputers to combine global weather observations with complex mathematical equations to provide reliable information about the future evolution of the atmosphere. One of the most important components of this modelling process is using a vast network of weather observations to generate an accurate snap-shot of the initial environmental conditions as a starting point - a process called initialisation.

Unfortunately, virus-related travel restrictions have caused a slump in aircraft-based weather observations around the world, which is likely to be affecting the initialisation process in global and regional NWP models.

According to the European Centre for Medium-Range Weather Forecasts (ECMWF), "the number of aircraft observations has gone down significantly over the last couple of weeks, both over Europe and globally. In the coming days and weeks, we expect a further decrease in numbers, which will have some impact on forecast quality in the short range."

Image: This graph shows a reduction in the number of aircraft-based observations (reports) over Europe received by the ECMWF during March 2020. Between March 3rd and 23rd, the ECMWF reported a reduction of 65% over Europe and 42% globally. Source: ECMWF

It's difficult to know exactly how much forecast performance will be affected in the coming weeks and months. Recent studies at ECMWF suggest that removing all air-craft based observations from the equation - which is not expected to happen during this pandemic - would degrade wind and temperature forecasts near the ground by around three percent. Higher up, these forecasts could degrade by as much as 15 percent at altitudes around 10-12 kilometres.

Fortunately, other types of weather observations are unlikely to be significantly affected by Coronavirus, such as satellites, weather balloons and ground-based weather stations.

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