Our dear friend, former colleague, mentor, and source of inspiration, Nils Gustafsson, has peacefully passed away after a period of illness. Many of us had the privilege of knowing Nils through his long tenure at SMHI. With his enthusiastic approach and extensive knowledge, he shaped an entire generation of researchers in numerical weather forecasting. Nils became a valued colleague and a cherished friend to many.

Nils had a unique ability to see the individual, showing genuine interest in everyone’s experiences and always eager to learn new things. His honest and straightforward style led to many stimulating discussions and successful collaborations. A defining trait of Nils was his inclusiveness; he believed in the power of collaboration and entrusted each person with significant responsibility. He often found his inner peace by ending the day with a few hours of computer programming. His main leisure interests included nature, hiking in the mountains, sailing, and spending time with his family.
We also fondly remember Nils’ great hospitality, hosting dinner parties, perhaps filled with political discussions, and often featuring lamb and red wine.

Nils was an internationally renowned researcher and a leader in his field. He fundamentally contributed to the development of regional numerical weather forecasts in Sweden, Europe, and worldwide. Nils excelled in developing methods for the assimilation of observations, earning SMHI a high reputation in this field of research. His international collaborative efforts led to the successful NWP consortia HIRLAM and ACCORD, which later provided the foundation for the MetCoOp joint operational systems. He taught meteorology worldwide, ensuring the transfer of knowledge to the next generation of meteorologists.

In 1967, a young Nils began his career at SMHI as a programmer. He studied meteorology at Stockholm University and continued to work with computers to develop a new data assimilation scheme based on optimal interpolation, successfully implemented operationally at SMHI in 1975. His groundbreaking research during this period focused on balanced relationships between different atmospheric variables and the use of satellite data. In the 1980s, Nils was part of the Nordic research team in Copenhagen that developed the first version of HIRLAM, a highly successful regional weather forecast model used operationally by SMHI and several other European meteorological services for decades. The HIRLAM collaboration expanded to about ten countries, with Nils playing a central role as international project manager and developer of advanced variational data assimilation, operational at SMHI in 1997. Nils’ expertise and connections also helped shape the current ACCORD collaboration, involving 26 countries in Europe and Northern Africa. Related to his data assimilation work, Nils developed a regional spectral model and recognized the importance of parallel computing early on.

Meeting new people and exchanging experiences was something Nils cherished. He contributed significantly to the training of meteorologists at the Department of Meteorology at Stockholm University (MISU), supervised many undergraduates and four PhD students, and lectured worldwide.

Nils was a genuin leader, deeply engaged, overall responsible, infinitely brave and boaderless honest.

We will never forget you, Nils. Our thoughts go out to your family, Jelena, Alisa, Maksim, Margarita and David.

With deepest sympathy,

Colleagues and friends at SMHI