What is a storm?

What is a Storm? 

The word ‘storm’ is frequently misused in the media and colloquially, almost as much as the misuse of the term ‘weather bomb’*.  In the strictest meteorological sense, a ‘storm’ is only a storm if accompanied by storm-force winds, which are defined by the Beaufort scale as having an average speed of over 47 knots (88 km/h). However, there are several other types of storm which don’t require storm-force winds.

Understanding the long range forecast

by Georgina Griffiths, senior meteorologist.

Resolution counts

Weather forecasting is basically an ‘initial value problem.’ This means that if weather models could capture the current weather perfectly i.e. correctly initialise the current state of the atmosphere, then in theory, they could forecast the future weather accurately well beyond the present limit of a week or so. After all, the atmosphere is a fluid, and follows strict laws of physics.

What makes a rainbow?

An explanation of atmospheric optical phenomena

Here at MetService, people often send us photos of interesting clouds, unusual weather, and also atmospheric optical phenomena. Atmospheric optics is the branch of physics which describes how light interacts with the Earth’s atmosphere, to create a wide range of visual spectacles. Things such as rainbows, ice haloes, and crepuscular rays all come under atmospheric optics, along with many others. These can be observed all around New Zealand under the right conditions.

It's a bird! It's a plane! It's radar interference!

Weather radars are used all around the world to detect rain, hail and snow, as it happens. However, there are times when the radar network can pick up other things as well. While you generally won't see aeroplanes on our radar images (the radar beam is usually beneath the flight path of most flights, and also our radars are calibrated to primarily pick up smaller objects, whereas radars at airports are calibrated differently to primarily pick up aeroplane-sized objects), there is a myriad of other things that can cause interference on our radar images, which I will explain in this blog.

Severe Weather 1-2-3

Written by Lisa Murray, Communication Meteorologist.

Sitting out in the middle of the ocean, New Zealand is vulnerable to weather extremes from all directions, from the remains of tropical systems barreling in from the north, to cold winter southerlies bringing a blanket of snow.

What is a fresh wind? An explanation of wind speeds and the Beaufort Scale

written by MetService Meteorologist Claire Flynn

Sometimes in MetService forecasts, you will see a forecast for “fresh northerlies”. But what exactly does the word ‘fresh’ mean? For many people, the word ‘fresh’ carries connotations of cool or clean air (eg the phrase ‘fresh air’). However, the word ‘fresh’ also has a more technical definition, that comes from the Beaufort Scale, which I will describe in this blog.

 

Mean Wind Speeds vs. Gust Speeds

A classic cold front on Sunday 24 April 2016

By meteorologist Emma Blades

As a cold front swept up the North Island on Sunday 24 April 2016 it was like a blanket had lifted leaving blue skies behind. In the classic cold-front scenario, showers usually follow the main rain band. But because the flow was west to southwest behind the front, the South Island was sheltering the North Island from the showers, resulting in clear skies behing the front in this case.