Cold Air Development

Weather Events

Parameter	Description
Precipitation	Thunderstorms, rain and hail showers during the whole life cycle.
Temperature	No remarkable changes.
Wind (incl. gusts)	Increasing wind during the development of the Comma to a full-scale vortex.
Other relevant information	In its development stages, the Comma tail is meteorologicaly more active with heavy convective development due to the left exit region of a jet streak (Jet Streak Model). Convective cells mostly develop within the Comma tail and move to the head where they dissipate. In the more mature stage, different conveyor belts are situated on top of each other and a Cold Front will develop.

The weather events are well illustrated using data from 28 January 2020 at 12 UTC, which is the time of the end stage of a CAD extending from the west of Ireland eastward to central Europe. This case is accompanied by strong weather activity, even Cbs but no differentiation between the former comma tail and comma head.

28 January, 12 UTC. Dust RGB; arrows indicate the cloudiness of the stage of the Cold Air development.

before after

28 January 2019, 12UTC: IR + synoptic measurements (above) + probability of moderate rain (Precipitting clouds PC - NWCSAF).
Note: for a larger SYNOP image click this link.

All available synoptic stations in the comma front, in a spiral southward to the Alps in Austria, show heavy rain and some also Cbs. Conversely, the precipitation probability of moderate rain (PC) seems to underestimate the real rain: the probability is between 35 and 55 %. Higher values appear along the windward side of the Alps. From an evaluation of this NWCSAF product it can be said that it generally displays such behaviour, that rain is usually observed alongside smaller probabilities.

before after

28 January 2020, 12 UTC, IR ; superimposed: 1st row: Cloud Type (CT NWCSAF) (above) + Cloud Top Height (CTTH - NWCSAF) (below); 2nd row: Convective Rainfall Rate (CRR NWCSAF) (above) + Radar intensities from Opera radar system (below)

For identifying values for Cloud type (CT), Cloud type height (CTTH), precipitating clouds (PC), and Opera radar for any pixel in the images look into the legends. (link)