Forecasting what is going to happen in the weather starts with knowing what IS happening in the weather. I’ve written about weather balloons, which supply that kind of real-time data. Of course, weather stations and satellites do the same thing. You might not know about the international supply of real-time weather data we get from almost every airplane that goes up! And now, obviously, not as many are going up.
Primarily, aircraft take measurements of temperature, humidity, pressure and wind as they ascend, fly at maximum altitude and then descend. They transmit those measurements back to weather services where that data is used for modeling the forecast. This is known as the AMDAR program (Aircraft Meteorological Data Relay). Take a look at the trend of relayed data on this chart (all you really need to know is that the transmissions are down by two-thirds this month).
The ECMWF, or European Centre for Medium-Range Weather Forecasts, which puts out the famous EURO model, illustrates the before and after lack of aircraft from March 2nd versus March 23rd:
Simply put, fewer aircraft flying means less weather data coming in for the models. How does this really translate? Here’s an example of WIND data from the European model where they compared using aircraft data and not using it. The first 12 hours showed the most deterioration in wind forecasting.
This article from the ECMWF explains the challenge. While satellite and other observational platforms supply billions of data every day, the lack of AMDAR can have a 9% to 13% impact on wind forecasts especially.
I emailed NWS forecaster Dan Reilly here in Houston who reiterated the European report. He wrote me:
"...the data are important but are only a small part of the data that feeds in. But there will be some impact as quoted in the EC media release:
"‘We are anticipating the substantial reduction in the availability of US AMDAR data to continue over the coming weeks, likely to generate some measure of impact on the output of our numerical weather prediction systems,’ says Christopher Hill from the US National Oceanic and Atmospheric Administration (NOAA).
“I think bottom line is there will be some impact but it’s hard to gauge exactly how much...but the EC link does quantify some of the ways.”
So we will still have very accurate weather forecasts in the weeks to come, but the sooner we get those planes back in the air, the better for all of us. In so many ways.