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
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Description
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Precipitation (incl. thunder)
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- 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.
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Temperature
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- Surface temperature and sea surface temperature are forcing features of convection.
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Wind (incl. gusts)
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- 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.
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Other relevant information
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- 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
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13 April 1999/06.00 UTC - Meteosat IR image; weather events (green: rain and showers, blue: drizzle, cyan: snow,
red: thunderstorm, black: no precipitation)
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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.