Observations definitely fell off a cliff as commercial air travel slowed to a crawl. In terms of impact, though… it turned out not to be a big deal.
> Aircraft reports suffered a 75% decline in numbers from mid-March to mid-April 2020; in May the number started increasing again. Despite the loss of data there is no clear signal in the forecast skill—partly because the skill shows considerable variability on daily, seasonal, and interannual timescales (Figures 3 and 4). …
> …
> Overall, we can find no evidence that the decrease in aircraft observations has handicapped numerical forecasts of extreme weather to an extent large enough to incur significant economic impact.
https://en.wikipedia.org/wiki/TAMDAR
Observations definitely fell off a cliff as commercial air travel slowed to a crawl. In terms of impact, though… it turned out not to be a big deal.
> Aircraft reports suffered a 75% decline in numbers from mid-March to mid-April 2020; in May the number started increasing again. Despite the loss of data there is no clear signal in the forecast skill—partly because the skill shows considerable variability on daily, seasonal, and interannual timescales (Figures 3 and 4). …
> …
> Overall, we can find no evidence that the decrease in aircraft observations has handicapped numerical forecasts of extreme weather to an extent large enough to incur significant economic impact.
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/202...