Looking at this further, I think both I and the author of the posted tweet both initially misinterpreted what these graphs represent. The horizontal axis is the

Looking at this further, I think both I and the author of the posted tweet both initially misinterpreted what these graphs represent. The horizontal axis is the date at which the forecast (or nowcast) was made. The Atlanta Fed made estimates for Q2 GDP every day in July, which is what was reflected in the archived version of the page. They didn't make a forecast of Q3 GDP until July 30, which is why there aren't earlier data points in the current version of the graph. That's also why the latest estimate in the archived version is -1.2% while the estimate in the current version is +2% - it's not a change in estimate, they're just measuring different things. Makes perfect sense when you know what you're looking at, but easy to misinterpret without context.