Cold and dry Arctic air masses moving from sea ice southward over the open ocean rapidly heat up, moisten, and form clouds. Diabatic heating and moistening rates in such marine cold air outbreaks (CAOs) are key to understanding their dynamics. While state-of-the-art atmospheric reanalysis products are commonly used to estimate these rates, the uncertainties of these reanalysis data sets especially in 4-dimensional space required to calculate them remain largely unspecified. Therefore, we present an analysis based on actual quasi-Lagrangian observations, which offer direct insights into these processes and which were conducted during the HALO-(AC)3 Arctic airborne campaign. From the measurements during a case study of a CAO on 01 April 2022, a maximum moistening and diabatic heating larger than 0.25 g kg-1h-1 and 6 K h-1, respectively, were deduced. Clouds forming within 30 minutes of the off-ice drift then intensified the vertical mixing. In the later stages of the CAO, maximum increases of solar albedo of around 0.03-0.06 h-1 were observed. We suggest that such data collected in a dedicated Lagrangian framework will serve as invaluable input for the benchmarking of numerical weather-prediction models and modern reanalysis products.