A depression gathered some warm moist clouds from Australia and brought them southwards across the North Island of New Zealand as a warm front. About the same time a chilly southerly marched out of the southern ocean. The moist clouds (aloft) and the chilly southerlies (near ground) met just east of Canterbury, providing the spark to make intense rain. This supplied energy to speed-up a passing jetstream, resulting in the direct removal of heaps of air out of the original depression. So its pressure dropped from 1002 to below 980hPa - most of this occurred in 24 hours, and at latitude 45ºC a drop of 20hPa in 24 hours is defined as 1B (one bomb).

Found this in a description of 11 - 13 October 2000 NZ snowstorm. Click on the link below to see the whole thing, weather maps aswell. Here is an example of how they can have an effect



Any knowledge on that?

http://www.metservice.com/default/index.php?alias=2000spring2194257