Why is the local weather forecast sometimes inaccurate even for the next few hours? This is not only due to the inaccuracies of forecast models, but also because of missing observations that drive weather prediction models. These observations are mainly missing between about 100 m and 1000 m above ground where there are no weather stations measuring temperature, humidity, and wind. Balloons and airplanes provide data only sporadically and not continuously, and this lowest layer of the atmosphere is relatively poorly resolved with satellites. At the same time, changes in meteorological variables in space and time are significantly more pronounced in this layer (100 m - 1 km) than at several kilometers in height. To improve weather forecasts, more measurements are needed in this range of altitudes.

During the VITAL II campaign, which is a research initiative within HErZ the participants (DWD and the universities of Cologne, Bonn, Tübingen, Hamburg, Munich and Frankfurt) aim to partially close this measurement gap over the summer of 2026. For this purpose, a dense network of remote sensing and ground stations will be operated in the Cologne Bay from June to August 2026, which will be combined with a novel geostationary satellite (Meteosat Third Generation Sounder 1) and supplemented with meteorological drone measurements during an intensive measurement period in August. These data are intended to capture the lowest 1-2 kilometers of the atmosphere over Cologne Bay in both time and space at a resolution not yet previously achieved. The measured atmospheric profiles are intended to be used to quantify the impact of the additional observations on weather forecasting, to improve the forecast models themselves, and to learn more about the development of thunderstorms and associated temperature drops.

Around 25 participating researchers met in Cologne from 9-11 February 2026 at the Kick-off workshop for the VITAL II campaign. During this workshop the measurement sites were visited and the specific conditions of the measurements (locations, time intervals, system configuration) were discussed and determined. The workshop participants included the DWD expert contact person Frank Beyrich who in particular advising the HIRES-APP project, which is leading the organisation of the VITAL II campaign, Maike Ahlgrimm (DWD) who is leading the HErZ competence area on "Model Development", and Anika Obermann-Hellhund (DWD) who is leading the HErZ competence area on the "Integration of Measurement Data and Modeling". All three DWD colleagues accompany and support the HErZ participants, e.g., by providing access to infrastructure, deploying and configuring measuring instruments, offering data storage options, and ensuring that the experience, insights, and results from the VITAL II campaign are beneficial for all participants and in particular for DWD.

The VITAL II campaign fulfills a strategic goal of HErZ, namely its strengthening as a network, and will in the future contribute to a second strategic goal of HErZ: achieving scientifically excellent results in basic research.

Participants on 10 February 2026 at a measuring site. Photo: U. Löhnert.