A regularly occurring weather pattern or singularity is defined as a deviation from the average annual course of meteorological elements that occurs on certain days in the annual calendar with reasonable regularity. The phenomenon of the March cold snap can be identified by the number of days on which snow falls (fresh snowfall events). Fresh snowfall becomes a less frequent occurrence by the end of February at the weather stations in eastern Switzerland (Einsiedeln, Elm, Lucerne, St. Gallen and Zurich). In the first few days of March, however, the number of fresh snowfall events picks up again until 6th March, both in the lowlands and all along the northern slopes of the Alps, up to an elevation of around 1,000 metres above sea level. An extreme cold snap with record-high snow levels was seen in the lowlands on the northern side of the Alps on 4th and 5th March 2006.