Pressure systems — lows and highs

The global atmosphere consists of high- and low-pressure areas whose motion determines the weather. In Central Europe lows typically travel from west to east.

Source: WMO; DWD Klimatologie; AMS Glossary.

Main direction of travel in Europe

The main direction of travel of pressure systems in Europe is West to East — driven by the polar-front jet stream.

Central European airspace lies in the zone of travelling low-pressure systems.

Seasonal shift

The zone of travelling lows in the Northern Hemisphere lies more northerly in summer than in winter due to the seasonal northward shift of the jet stream and polar front:

Summer: polar-front jet at 50-60° N → fewer lows over Central Europe, more stable highs.
Winter: jet at 40-50° N → more lows over Central Europe, more frequent weather changes.

High-pressure areas (highs, anticyclones)

Dynamic high

A dynamic warm high develops by wide-spread subsidence of air:

Air sinks from altitude → warms adiabatically.
Surface pressure rises.
Result: stable, clear atmosphere, good visibility.

Weather in a dynamic high (summer)

In the centre of a dynamic high-pressure system during summer, expect clear skies or shallow cumuliform clouds forming below a subsidence inversion due to descending stable air that suppresses significant convection and precipitation:

Nice weather in a dynamic high-pressure system typically results from a subsidence inversion caused by widespread descending air that dries the atmosphere above the inversion layer, dissipating existing clouds and promoting stable, clear conditions.

Weather in a dynamic high (winter)

Fog or high fog can develop below a surface inversion, the type of weather to be expected in the centre of a dynamic high in winter (see fog lesson).

Thermal high (cold high)

Thermal high (cold high) develops in Central Europe by advection and subsidence of cold air behind a cold front:

Cold heavy air sinks → raises surface pressure locally.
Typical behind a cold front in winter — cold, dry air and clear sky.

High-pressure wedge / ridge

A wedge of high pressure in aviation weather reports is a strung-out zone emanating from the centre of a high-pressure area, filled with warm air where stable atmospheric conditions prevail.

A "ridge of high pressure" is a zone of high pressure which connects two high pressure areas.

Intermediate high

An intermediate high is a relatively high atmospheric pressure between two low pressure areas; calming of weather processes:

Brief fair-weather phase between two lows.
Typically 1-2 days.

Low-pressure areas (lows, cyclones)

Dynamic low

A dynamic low-pressure area develops by convergence of air masses close to the ground and resulting lifting of air:

Air converges at the surface → rises.
Surface pressure falls → low.

In a dynamic low the weather is usually bad because air is lifted due to the convergence close to the ground, is thereby cooled and clouds and precipitation can develop.

Thermal low (heat low)

Thermal low (heat low) develops by intense solar radiation, regional heating and a decrease in air density:

Ground heats strongly → air rises → surface pressure falls locally.
Typical over heated areas in summer (Mediterranean, Iran, Sahara).
Often with thunderstorm potential.

High trough

A high trough in aviation weather reports is a strung-out, mostly elliptical area of low pressure emanating from the centre of a low-pressure area, filled with cold air where pressure levels are lower than in the surrounding vicinity.

At a (high) trough, usually convective clouds, showers and thunderstorms must be expected.

Cold cut-off low

A cold cut-off low is a local low-pressure area prevalent only at altitude, characterized by significantly lower temperatures in its centre compared to the surrounding air:

Low "cut off" from the main flow.
Persistent, slow-moving.

A cold cut-off low in summer typically features predominantly dense clouds, showers, and thunderstorms, with weather phenomena varying based on position in front of, within, or behind its centre.

Pressure symbols on weather charts

H or HIGH — high-pressure centre.
L or LOW — low-pressure centre.
L 995 on charts = the centre of a low pressure area with a core pressure of 995 hPa.

Three-day VFR / sport forecast

From a three-day forecast for VFR flights and aviation sports, the weather situation and development of individual weather elements for the following three days for VFR pilots, balloonists and glider pilots can be obtained.

Klimatologie*; AMS Glossary; FAA-H-8083-25B PHAK Ch. 12.*