Comma - Weather Events

by ZAMG and KNMI


Commas can be split into a head and a tail, whereby the head clouds are layered cloudiness with dynamical precipitation and the tail clouds are more convective cloudiness with showery precipitation.

Parameter Description
Precipitation (incl. thunder)
  • Moderate to heavy precipitation, rain or snow, in Comma head
  • In Comma tail more showery precitation
  • In Comma tail quite often hail and thunderstorms are observed.
Temperature
  • Surface temperature and sea surface temperature are forcing features of convection.
Wind (incl. gusts)
  • In surface trough strong winds can be expected.
  • Ahead of the Comma head strong gusts are common.
  • In and near showers also strong gusts can be observed.
Other relevant information
  • Risk of moderate to severe icing and turbulence
  • Poor visibility during heavy snowfall
  • Heavy snow fall can cause hazardous weather for society
  • Different behaviour over sea and land

13 April 1999/06.00 UTC - Meteosat IR image; weather events (green: rain and showers, blue: drizzle, cyan: snow, red: thunderstorm, black: no precipitation)
In the example from 13 April 1999/06.00 UTC the Comma head extending from N. Ireland to Scotland is accompanied by reports of rain and snow, whilst the Comma tail over central England has fewer reports of precipitation.

Menu Of Comma
Typical Appearance In Vertical Cross Sections
References