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Table 1 Upper level weather types - description and abbreviations

From: Weather patterns and occurrence of epileptic seizures

Ridge (R) A ridge is an elongated area of relatively high pressure extending from the centre of a high-pressure region. The upper level ridge (the height contours bend on upper level synoptic chart strongly to the north) are accompanied usually by warm and dry weather conditions at the surface.
Non gradient field in ridge (NG-R) There is no significant flow of air in the upper levels of the atmosphere. For a more detailed analysis we could discriminate non-gradient field in ridge (NG-R) and in trough (NG-T). The weather at the surface can be stable, without any wind, but also there can be local instability as well due to convective development, especially in summer.
Non gradient field in trough (NG-T) There is no significant flow of air in the upper levels of the atmosphere. For a more detailed analysis we could discriminate non-gradient field in ridge (NG-R) and in trough (NG-T). The weather at the surface can be stable, without any wind, but also there can be local instability as well due to convective development, especially in summer.
Front side of the ridge (GNW) Transitional state between ridge and trough where flow in upper level move from northwest to southeast. The north-westerly flow at the front side of the ridge tends to bring colder and sometimes more humid air.
Back side of the trough (NWS) Transitional state between ridge and trough where flow in upper level move from northwest to southeast, bringing usually colder and drier air. At surface weather could be associated with stable and windy weather.
Back side of the ridge (GSW) Transitional state between trough and ridge where flow in upper level move from southwest to northeast, bringing usually warmer and wetter air. At surface weather could be associated with changeable clouds and moderate to strong wind.
Front side of the trough (SWS) Transitional state between trough and ridge where flow in upper level move from southwest to northeast, bringing usually warmer and wetter air. At surface weather could be associated with changeable clouds, sometimes with occasionally rain, moderate to strong wind and warmer conditions than before.
Trough (T) A trough is an elongated area of relatively low pressure extending from the center of a region of low pressure. The upper level troughs (the height contours bend on upper level synoptic chart strongly to the south) are typically preceded by stormy weather and colder air at the surface.
Upper level low (ULC) Upper level lows are closed cyclonically circulating eddies in the middle and upper troposphere. They are sometimes also called “cold drops”, because the air within an Upper level low is colder than in its surroundings. Upper level lows have been responsible for bringing high amount of precipitation (e.g. heavy snow in the winter) especially if it is stationary. It may or may not have to be connected to surface low.
Northerly flow (NS) Air in upper level move from north to south, with parallel height contours on upper level synoptic chart, bringing usually colder air. The weather at the surface could be sunny but chilly.
Northeasterly flow (NES) Air in upper level move from northeast to southwest, with parallel height contours on upper level synoptic chart. The weather at the surface could be accompanied by colder and windy conditions.
Southerly flow (SS) Air in upper level move from south to north, with parallel height contours on upper level synoptic chart. At surface weather could be associated with strong and stormy wind, sometimes accompanied by precipitation.
Southeasterly flow (SES) Air in upper level move from southeast to northwest, with parallel height contours on upper level synoptic chart. The weather at the surface could be mild and humid, especially in w inter.
Westerly flow (WS) Zonal flow, where air in upper level usually move from west to east, with parallel height contours on upper level synoptic chart, tends to result in mild, changeable weather at the surface.
Easterly flow (ES) Air in upper level move from east to west, with parallel height contours on upper level synoptic chart. The weather at the surface is characterized by strong winds, cold and cloudy weather and very often with precipitation.