There is a strong northwesterly wind that blows across New Zealand’s South Island which is said to have a disturbing effect on the local population.

The Nor’wester, as it is known, sends temperatures soaring as it sweeps across the Canterbury Plains and has been statistically linked to increases in suicide and domestic violence. Some people feel elated when the dry, hot air hits, but most feel depressed, irritable and drained of energy.

However The Nor’wester also brings with it one of the rareties of the skies, a cloud with its own name. The Nor’west Arch is a distinctive altocumulus formation which partly takes its name from the wind that hurries it along and partly from its shape, because it appears as an arch of high white cloud in an otherwise clear blue sky. It is also often referred to as the Canterbury Arch.

This weather pattern is peculiar to the South Island’s east coast. Warm moist air from over the Tasman Sea is pushed up by the Southern Alps, causing it to cool rapidly, and much of the moisture is dumped on the west coast. As the air passes over the alps, the water vapour remaining becomes visible in a band of cloud over the mountains at the top of each wave of air. To a viewer on the eastern side, this appears as an arch of cloud.

The standing wave of The Nor’west Arch is caused by the moisture condensing and becoming visible towards the top of the wave and then evaporating again as the air descends to the trough of the wave.

Let’s hope this impressive sight helps lift the depression caused by the fiery blasts that accompany it.

 

Current Cloud of the Month:
July 2010

Previous Clouds of the Month:
June 2010
May 2010
April 2010
March 2010
February 2010
January 2010
Cloud Reflections (December 09)
Numbers in the Clouds (November 09)
Sun Pillar (October 09)
Convection Clouds (September 09)
‘Pile d’Assiettes’ (August 09)
Cumulus congestus (July 09)
‘Asperatus’ (June 09)
Clouds at Night (May 09)
Sundogs (April 09)
Diamond Dust (March 09)
Cloud Streets (February 09)
Crepuscular Rays (Jan 09)
Valley Fog (December 08)
Cloud Shadows (November 08)
Contrails (October 08)
Mamma (September 08)
Kármán Vortex (August 08)
The Summertime Halo (July 08)
The Nor’west Arch (June 08)
Microbursts (May 08)
Irridescent Clouds (April 08)
Northern Lights – Aurora Borealis (March 08)
Ice halos (February 08)
Lightning (January 08)
Roll Cloud (December 07)
Banner Cloud (November 07)
Stratocumulus (October 07)
The Unclassified Cloud (September 07)
Alexander’s Dark Band (August 07)
Fumulus Snail (July 07)
Distrail (June 07)
Altocumulus undulatus (May 07)
Cumulonimbus capillatus (April 07)
Lacunosus (March 07)
Horseshoe Vortex Cloud (February 07)
Jet-Stream Cirrus (Janurary 07)
Altostratus/Altocumulus/Altowhateveritis (December 06)
Anti-Crepuscular Rays (November 06)
Stratocumulus (October 06)
Altocumulus (September ’06)
The Kelvin-Helmholtz Wave Cloud (August ’06)
The ‘Brocken Spectre’ (July ’06)
‘Whale’s Mouth’ (June ’06)
Noctilucent (May ’06)
Cirrus (April ’06)
Cap Cloud (March ’06)
Fallstreak Holes (February ’06)
Nacreous (January ’06)
Cirrostratus (December ’05)
Tuba (November ’05)
Virga (October ’05)
Cirrocumulus (September ’05)
Altostratus (August ’05)
Cumulus (July ’05)
Mamma (June ’05)
Pileus (May ’05)
Lenticularis (April ’05)
Stratus (March ’05)
Cumulonimbus (February ’05)
Contrails (January ’05)


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