The snow that closed the Desert Road and Napier-Taupo Road from Sun 4th to Tue 6th October 2009 was unseasonable. It was caused by a low pressure system deepening over the area at the same time as a cold southerly flow arrived, resulting in moist air being cooled from below in a cauldron of lowering pressure. This produced an unusually heavy amount of snow over a wide area. The weather map for noon on Sunday shows the low pressure system forming over the Central North Island
A summary of the equinox
I started tramping as a teenager with the expectation of rain in the hills about two days out of three. So we were always prepared to change plans if confronted by a river in flood. Likewise, conditions on the tops could send us scurrying back below the bush line, as the wind over the ridge crests was sometimes strong enough to throw an adult carrying a heavy pack off their feet.
Earlier in the September 2009 many parts of New Zealand had frosts. This is the beginning of spring so it got me thinking about the impact that late season frosts can have on the delicate buds sprouting on trees and vines around the country.
Our weather in New Zealand is greatly modified by the shape of the land. There are many parts of the country where the air is channelled through gaps in the terrain, and I thought I would write a little about this. Especially since it relates to the thread of my earlier posts on wind.
On 21 August in 1861, Dr. Charles Knight was appointed the first Director of Meteorological Stations in New Zealand.
His appointment marked the founding of the New Zealand Meteorological Service – this country’s oldest continuous scientific institution. Early missionaries and settlers quickly realised our coasts were subject to rapid changes of weather, with frequent violent storms. In the 1840s and 1850s weather studies were made by military officers, but in 1859 the government put weather stations on a more formal footing.
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).
In my blog post about winds aloft there is a loop of satellite images for a week in winter 2008. It shows that the big cloud features in the mid-latitudes typically travel from west to east. In other words, the features you see on weather maps affecting New Zealand have usually started out roughly in the area of southern Australia.