Why is the weather stuck?
This week the weather across New Zealand will be like one of those hurry up and wait moments. That's because the atmosphere is in a giant go-slow.
It all starts with the big high that drifted east of New Zealand at the start of the long weekend. It is in no hurry to move. Think of it as a big water buffalo!
This week’s unsettled weather pattern will take it's time to go away and changes will be slow to come. So why has the weather been putting on a go-slow with this slow moving blocking high?
It has to do with the abundant warm air in the mid-levels of the atmosphere spilling down from it's source region in the tropics north of New Zealand and back westwards to Tropical Australia.
Have a look at the 500hpa map for early this week. All the yellow and orange is warmer air.
As this warm air (yellow and orange) spreads down from the tropics it engulfs the incoming blob of colder air ( blue and green) from the southern Ocean. It in turn chokes off the approaching front and the low subsequently pin-wheels in place with no where to go.
In the breaks between the highs there are wet zones or atmospheric rivers. At the centre of the upper ridges the weather stays dry and settled. At the moment New Zealand is in the wet zone of this flow.