A surprising repercussion of the COVID-19 pandemic is that the accuracy of weather forecasts has gone down.

Weather is a big deal on a farm, and I use both the Dark Sky and AccuWeather apps to prepare for what's coming. But a couple of weeks ago, I noticed the forecasts going wonky. They'd say a week of rain was coming, and it wound up being clear. Or vice versa. And temperatures were off.

Now I've learned why: The mass grounding of flights. I had no idea weather forecasters harvested data from commercial airlines, but according to the World Meteorological Organization,

"The significant decrease in air traffic has had a clear impact [on forecast accuracy]. In-flight measurements of ambient temperature and wind speed and direction are a very important source of information for both weather prediction and climate monitoring.

"Commercial airliners contribute to the Aircraft Meteorological Data Relay programme (AMDAR), which uses onboard sensors, computers and communications systems to collect, process, format and transmit meteorological observations to ground stations via satellite or radio links."

United Nations News gets into the actual numbers, and points out that things are worse in Europe than in America:

"Before the COVID-19 era, commercial airlines took around 700,000 daily readings of air temperature, wind speed and wind direction. This data and much more is fed into WMO's Global Observing System, which supports weather and climate services and products provided by the 193 WMO Members.

"In Europe…air traffic readings are down by 85 to 90 per cent…. The impact has been less severe in the US, where commercial airline traffic data is down by 60 per cent, WMO said.

"'At the present time, the adverse impact of the loss of observations on the quality of weather forecast products is still expected to be relatively modest', said Lars Peter Riishojgaard, Director of WMO's Earth System Branch. 'However, as the decrease in availability of aircraft weather observations continues and expands, we may expect a gradual decrease in reliability of the forecasts.'"

While we still have satellites, ground-based weather stations and weather balloons, it appears the massive amounts of data harvested by airplanes is pretty crucial in meteorological modeling. With less planes in the air, there's a lot less data. Guess I'd better do what the older folks do down here, and start relying on my own joint pain to warn me of when a storm's coming.