Table Of ContentThe New Zealand
Weather Book
The New Zealand
Weather Book
Erick Brenstrum
First edition 1998
Reprinted 1999, 2001, 2003, 2007
Published by Craig Potton Publishing, Box 555, Nelson, New Zealand
Copyright ©text Erick Brenstrum, 1998
Copyright ©photographs, diagrams and illustrations as credited on page 126
The right of Erick Brenstrum to be identified as the author of this work in terms
of section 96 of the New Zealand Copyright Act 1994 is hereby asserted.
All rights reserved. Without limiting the rights under copyright reserved above,
no part of this publication may be reproduced, stored in a retrieval system, or
transmitted in any form, or by any means, electronic, mechanical, photocopy-
ing, recording, or otherwise, without the prior written permission of both the
copyright owner and Craig Potton Publishing Ltd.
ISBN 978-0-908802-47-0
Editor: James Brown
Printed in China by Everbest Printing Co. Ltd
Contents
Acknowledgements 7
Chapter 1 Understanding the Weather – Key Principles 9
Chapter 2 Meet the Weather Map 13
Chapter 3 Showers Showers Almost Everywhere 21
Chapter 4 More on Highs and Lows 29
Chapter 5 A Closer Look at Fronts 39
Chapter 6 Frosts and Fogs 45
Chapter 7 Thunderstorms, Hail and Tornadoes 51
Chapter 8 Snow 63
Chapter 9 Coastal Winds 71
Chapter 10 Convergence Lines 79
Chapter 11 Ex-Tropical Cyclones 87
Chapter 12 What Does It All Add Up To? 97
Chapter 13 Forecasting 115
Conclusion 125
Contributors 126
Index 127
One of the classic signs of a thunderstorm, these bulges – known as mamatus – typically form on the underside of the anvil of
cumulonimbus clouds. They can also form on the underside of high wave clouds formed when the wind blows across a mountain range.
6
Acknowledgements
First, I would like to thank my colleagues past and present who have taught me so much:
in particular the late Tom Steiner who got me started in meteorology and supported my
research; Rod Stainer for his encouragement and for giving me the time to write my
first articles for New Zealand Flight Safety; Ray Smith who gave me the opportunity to
write for New Zealand Geographic; Alex Neale and the late Henry Hill for the example
they set in their studies of the weather; and Augie Auer for his encouragement and
support and for being a frequent sounding board for meteorological ideas.
Kennedy Warne at New Zealand Geographic has published my articles over the last ten
years. His enthusiasm for matters meteorologica l is unfailing. Some of the explanations
and anecdotes used in this book first appeared in New Zealand Geographic as did a number
of the illustrations. Jim Renwick of NIWA has been my safety net checking the manuscript
for errors – any that may remain are entirely my responsibility. Warren Gray and Brett
Mullan, also at NIWA, supplied the radar images and SOI graph respectively, and Steve
Ready at MetService the cyclone tracks map.
Thanks must also go to MetService for the use of the weather maps, to the Japanese
Meteorological Agency (JMA) for the GMS satellite photos, to Wayne Carran for his
magnificent avalanche photo, and to Arno Gasteiger for finding just the right 44,000
year old tree to photograph using only my vague directions for guidance. The staff at the
Alexander Turnbull Library were so friendly and helpful it makes me want to go back and
do another book. Special thanks to my long-time friend Mike Bradstock who encouraged
me to embark on this project.
Robbie Burton and Dave Chowdhury at Craig Potton Publishing made it all happen:
my thanks to them for their vision and enthusiasm and for dragging me through the hard
bits. My thanks also go to Craig Potton for the use of some of his incomparable photos.
I owe a special debt to my editor James Brown, who was everything I could want in an
editor – enthusiastic, firm, almost invariably right, and gifted in the mother tongue.
Most of all I would like to thank my family, in particular my wife Alex and children
Hugh and Anna, for their patience and understanding. This took longer to write than
originally intended – most of it borrowed or stolen family time. I could not have got there
without your encouragement and support.
Finally, all credit to the weather for turning up.
Erick Brenstrum
7
“Under so plain a title neither abstruse problems nor intricate difficulties should be found.
This popular work is intended for many, rather than for few, with an earnest hope of its
utility in daily life. The means actually requisite to enable any person of fair abilities and
average education to become practically ‘weather-wise’ are much more readily attainable
than has been often supposed. With a barometer, two or three thermometers, some brief
instructions, and an attentive observation, not of instruments only, but the sky and at-
mosphere, one may utilise Meteorology.”
Robert FitzRoy, a former New Zealand governor and pioneer meteorologist, in his The Weather Book: a
manual of practical meteorology published in 1863.
8
CHAPTER 1
Understanding the
weather – key principles
The weather at its most violent is a killer. The wind can destroy buildings, sink ships, throw
planes from the sky and drive the ocean up onto the land. Heavy rain causes landslides
and floods; extremes of heat and cold are a threat to both people and animals.
The weather is also a lifegiver. Rain and sun make plants grow, providing much of the food
that sustains us, and a spectacular sunset nourishes the soul. The weather is fascinating
in the way it changes, and a good understanding of how it evolves enables us to avoid its
greatest dangers and enjoy its benefits.
The air in the sky around us is the factory in which the weather is made. Any attempt
to understand the weather must begin by looking at what air is made of and how it
behaves. The main raw ingredient in this aerial factory is water, so it is also important
to understand how water is transformed as it travels through the sky from gas to liquid
or solid.
THE ATMOSPHERE
The atmosphere is a thin layer of gas clinging to the Earth’s surface. To
get some idea of how thin it is, compare it to an apple cut in half. If the
Earth was shrunk to the size of the apple, then the atmosphere would
be as thick as the apple skin.
The atmosphere is a mixture of gases, mostly nitrogen (75%) and
oxygen (23%), as well as other gases in smaller concentrations. Because
the atmosphere is well mixed by the wind, the proportion of these is
relatively constant from day to day, with one important exception: water
vapour. Water vapour varies from near 0% to 4% of the atmosphere.
This is because water is constantly evaporating from the ocean into the
atmosphere and then falling out again as rain or snow.
AIR DENSITY
The density of the air is a measure of how much air is present in a cube
with sides one metre long. At sea level, air density is about 1.2 kg per Blanketing the land, a layer
cubic metre, while on top of high mountains like the Himalayas, it is only about one third of low cloud is trapped
under an anticyclone while
of this. On top of Mount Everest therefore, each lungful of air gives your body only one
the mountain tops are in
third as much oxygen as at sea level.
clear skies.
People whose ancestors have lived at high altitude for thousands of years, such as the
KEY PRINCIPLES 9
