Thursday, May 27, 2010

Flooding in Christchurch

Thursday, May 27, 2010
This in from an news paper article oldbearnews editoryesterday - it kinda explains NZ weather systems!
Suffice to say we don't get long periods of WARM sunny summer weather neither. I am told that the wild life at willowbank wildlife reserve (just up the road from us) is having a ball - in particular these otters.

Once in a while, like this week, New Zealand becomes home to a family that just does not want to leave.

The family in question is an unwelcome brood of spiralling low pressure systems spreading gloom and misery.

During the past few days the country has been targeted by a large and deepening area of low pressure, the likes of which we have not seen across the South Island since July 2008.

Rain bands, stalled warm and cold fronts and small, spinning depression centres within this bigger feature have brought heavy rain and are about to serve up high winds and even snow to low levels. Weather systems in New Zealand generally race across from west to east, bringing the rapidly changing pattern we all know and grudgingly accept as normal. But occasionally, as we are experiencing this week, the brakes go on.

What happens is determined by things higher in the atmosphere. Strong winds at altitudes of between 6000m and 10,000m steer surface low and high pressure systems, which then determine the weather at ground level.

The complex trough of low pressure bothering us this week is unfortunately stuck underneath a large upper-level trough, which means nothing is moving fast. The general trend is for the storm system to slowly shift out to the east of the South Island, but computer models indicate it will not be until the end of the weekend.

What makes forecasting even more difficult in this situation is that each small depression centre within the main system is not only spinning itself, but is rotating around the other centres, like a whirlpool or a troupe of ballet dancers pirouetting around each other. With no strong winds above to move them on, they keep spinning and heading back towards the country.

One thing is for sure: nothing is going anywhere in a hurry.

bear print

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