The Meteorological Auto Code (MAC) and Numerical Weather Prediction (NWP) at SMHI

Type: Report
Series: RMK 117
Author: Författare Lennart Bengtsson, Nils Gustafsson1), Bo Döös2), Daniel Söderman, Lars Moen3), Thomas Thompson4), Paul Jakobsson, Gunnar Bleckert, Ann-Beate Henriksson, Bo Lindgren5) and Per Kållberg 1)Correspondig author, e-mail: 2)Deceased 2010 3)Deceased 2006 4)Deceased 2015 5)Deceased 2005


Sweden was a pioneering country in the development of NumericalWeather Prediction (NWP). The worlds first operational numerical forecast was produced already in 1954 by the International Meteorological Institute in Stockholm. SMHI started a bit later, but in 1961 a long term program for development of NWP was initiated. The activities grew gradually during the 1960’s and resulted in a core component for the SMHI forecast services. An early challenge was to overcome the limited computational resources with slow computational speed, small memory size and primitive software support. It was necessary to compensate for these limitations with dedicated work and creativity. A core component in this work was the software system MAC (Meteorological Auto Code) that was developed by the NWP group at SMHI. The MAC system is described in detail in this report and it included all computational software needed for the weather service, for example numerical models, objective analysis techniques, automatic data extraction, quality control of observations as well as forecast products in graphical or digital form.

We hope that this report will provide the younger generation with some insight into the conditions for development of NWP during the 1960’s.