This economist thinks the reason is that inputs were up in January and the calculation is treating that as less domestic production rather than increased inventories:
OK, so what can we say about the current forecast of −2.8% for Q1 of 2025? First, almost all of the data in the model right now are for January 2025 only. We still have 2 full months in the quarter to go (in terms of data collection). Second, the biggest contributor to the negative reading is a massive increase in imports in January 2025.
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The Atlanta Fed GDPNow model is doing exactly that, subtracting imports. However, it’s likely they are doing it incorrectly. Those imports have to show up elsewhere in the GDP equation. They will either be current consumption, or added to business inventories (to be consumed in the future). My guess, without knowing the details of their model, is that it’s not picking up the change in either inventories or consumption that must result from the increased imports.
This economist thinks the reason is that inputs were up in January and the calculation is treating that as less domestic production rather than increased inventories:
https://economistwritingeveryday.com/2025/03/05/understanding-the-projected-gdp-decline/