In the temperate regions, the number of storms and their strength is especially dependent on the strength and the flow pattern of the circulation in the upper air. In previous decades, above the northern part of the Atlantic Ocean this circulation has become stronger than is was before. Besides, the flow pattern was displaced to the north. It is not clear to what degree (if at all) this change in air circulation is related to the enhanced greenhouse effect, caused by humans.

Measurements at KNMI-stations in the Netherlands show that the total number of 'storms' (>= 6 Bft inland, or >= 7 Bft along the coast) has decreased since 1962 (Figure 11). On average, these events occur about 10 times per year. However, at present we experience 20-40% less of such 'storms' when compared to the beginning of the sixties. The Netherlands is too small and the observational series too short to detect changes in the number of heavy storms (at least 10 to 11 Bft). These storms occur in the Netherlands too seldom for trend detection, on average less than once per year.