[rnovak]

wait a second. The OP was comparing "aftcasting" TO "forecasting" 2-3 days in advance, and that's what my statement was based on.

If your 2-3 day forecasting is off by 5-6 degrees (celcius), why would your "aftcasting" forecast for 200 years ago be any more accurate if it is "just as good" as a 2-3 day forecast? That means I would expect an error of 5-6 degrees, same as a 2-3 day forecast

edit: formatting

[cryptoz]

If everyone is nitpicking that part of my comment, it would be worth noting that I was paraphrasing from the paper I linked.

> For the beginning of the twentieth century, the errors of such upper-air circulation maps over the Northern Hemisphere in winter would be comparable to the 2–3-day errors of modern weather forecasts.

Might be worth reading the abstract / full paper if you're interested in the topic.

[rnovak]

what's the actual error bound on both forecasts and aftcasts?

The article this discussion is linked to is claiming "1.46°F (0.81°C)" variance over recorded history. Recorded meaning they know what actually happened.

But I cannot believe that 2-3 day forecasts are accurate to within 2 degrees. Even the services linked by other commenters criticizing my original point claimed only 77% accuracy in the best case,