Deviation of 850 hPa-temperature from long-term mean

For each day of the year, the long-term mean temperature conditions in the 850 hPa level can be specified, ie the mean temperature at a height of about 1500 meters above sea level.

The character and origin of an air mass can be seen particularly well aloft. Near the earth's surface the actual properties of an air masses are influenced and modified by many processes.

The maps show the difference between the temperature predicted by an weather forecast model and the long-term mean temperature for a given day at around 1500 meters. With the color scale it is possible to determine whether an area has an above-average warm or cold air mass.

In most cases, the temperature conditions at the 850hPa level allow conclusions about the expected temperatures near the surface. Only in winter, high air temperatures do not necessarily mean high temperatures near the surface. Especially under high pressure influence there is a very stable stratifiction of the atmosphere preventing any vertical mixing of the air. At low lying areas and in valleys cold and humid air masses remain which are prone to fog, too.

In summer, a large and persisting temperature surplus at 850hPa level indicates an imminent heat wave near the surface.