Summertime convection

In the English language we have many words in common usage that have related but more specific meanings in a scientific and mathematical context. The key word of this blog post, “convergence”, is a good example of this. We sometimes hear of people’s views on some matter initially disagreeing and then, later, coming together or “converging”. In fluid dynamics we’re often interested in regions where different air flows come together. We call this type of flow convergence, and say that the air is converging. 

In the days following Wednesday 6 July 2011, stormy westerly conditions affected New Zealand. In this blog, we'll look at why.

The "Long Waves"

Below is the mean sea level analysis - the weather map - for 6am Sunday 10 July. In between big highs over the mid South Pacific and south of western Australia is a really large trough; it's the area shaded light blue. The weather map looked like this, more or less, since Wednesday 6 July: that is, the big features on it aren't moving much.

Written by Chris Webster, Meteorologist

The last week in January 2010 will be remembered by many over the central North Island for the frequent thunderstorms that developed in the afternoon, often lasting well into the evening. Conditions changed little during the week with a slack pressure gradient over the North Island allowing afternoon sea breezes to combine with abundant low level moisture, triggering heavy showers and thunderstorms inland. Many of these storms were slow moving, prompting a number of Severe Thunderstorm Warnings as radar detected torrential rain and hail in some cells.

One of the pleasures of reading history is coming across stories about the weather. Thunderstorms often figure in these. One of the most dramatic examples was recorded in the sixth century AD, by Gregory, Bishop of Tours, in his Historia Francorum (The History of the Franks).

Cumulonimbus cloud is not a common part of the Wellington cloudscape ...