I picked this up a day or so ago from the Metservice.

"Weather Bomb" v "Bomb Low"

It's the middle of summer and New Zealand is experiencing an explosive low-pressure system, aptly named a "bomb low".

New Zealand frequently, and incorrectly, uses the term "weather bomb" to describe bad weather events.

MetService communications meteorologist Lisa Murray said it was embarrassing even Wikipedia pointed out Kiwis' incorrect use of the term. In fact, there was no such thing as a "weather bomb", scientifically speaking.

While "weather bomb" isn't technically a scientific term, a "bomb low" is, and New Zealand is being hit with an explosion of wind and rain.

So what is a "Bomb Low"?

The bad weather that exploded onto New Zealand shores on Wednesday and Thursday is technically referred to among meteorologists as a bomb low.

This is essentially a rapidly deepening low-pressure system.

Murray said the process of rapidly deepening pressure was called "explosive cyclogenesis", and differed from everyday "passive" lows.

The rapidly deepening surface pressure came about when warm air met cold air.

Bomb lows typically passed over quickly. In this instance, most of the weather associated with the bomb was expected to be gone by Thursday evening.

A bomb low also left cold temperatures as a parting gift - just as this one was expected to do, Murray said.

It wasn't unusual to experience a bomb low in New Zealand but it was unusual for one to touch down during summer.

WHAT'S THE DIFFERENCE BETWEEN A BOMB LOW AND A WEATHER BOMB?

Technically, there's no such thing as a "weather bomb".

"There's no official scientific term that's a weather bomb," Murray said.

New Zealand adopted the phrase to explain almost any bad dumping of rain and wind. This week's bomb low has also been referred to in this way.

But it's not something you'd hear the MetService meteorologists saying from behind their computers.

Source: stuff.co.nz