Cut-off lows in forecasts
A cut-off low is defined by a high-altitude pocket of cold air and lower air pressure. In some cases, the upper-level low is strong enough to also generate a surface low, but that is by no means always the case.
It is therefore very difficult to recognise these phenomena on the surface weather map (with plotted isobars and fronts) or in forecast maps. In general, cut-off or upper-level lows are mentioned in the weather reports prepared by our forecasters.
The following example, from 14 November 2022, can be analysed using the surface pressure chart (showing isobars and fronts), as well as the weather report, both of which were available in our mobile app or on our website. If you only consider the surface pressure chart, it is not clear whether the rain forecast in Bern is triggered by the distant cold front. The bulletin, which can always be found above the surface pressure chart (with its isobars and fronts), can reveal this secret: a cut-off low is predicted to pass through on 14 November 2022.
It is therefore clear that the weather will be changeable and rainy on Monday. Moreover, when a cut-off low is present, there is greater uncertainty in the weather forecast. Accordingly, automatic forecasts should be treated with a certain degree of caution.