COMMA - WEATHER EVENTS

by ZAMG


Commas can split in a head and a tail, whereby head clouds are layered cloudiness with dynamical precipitation and Comma 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 rain and snow reports; the Comma tail over central England has fewer reports of precipitation.

SUB-MENU OF COMMA
TYPICAL APPEARANCE IN VERTICAL CROSS SECTIONS
REFERENCES