Does this show potential instability and conflicting airmass

[C-Nimbus]

Please have a look at the attached pressure map.

Does the light blue air sandwiched between the warmer air over NZ indicate potential instability?

Does this point to some action over central NZ for later today and 2moro?

[NZstorm]

Yes, it does show potential instability.

There is potential for thunderstorms, particularly over the North island.
An influx of moist air(from the north) looks to be on the cards. The dewpoint at Cape Reinga is on the rise. Put moist air into this trough and there will be interesting weather.

[spwill]

Looking at the Satellite, I dont see much rain for Auckland at the moment.
Looks like plenty of rain for central NZ with heavy falls mainly near the mnts.

[TonyT]

Please have a look at the attached pressure map.

Does the light blue air sandwiched between the warmer air over NZ indicate potential instability?

Does this point to some action over central NZ for later today and 2moro?

No, it doesnt.

The map doesnt show temperature it shows surface pressure and 500Hpa height. There is a relationship with temperature when you subtract one from the other (its call thickness) but this map doesnt show it.

[NZstorm]

Tony, height is strongly correlated to temperature.

A low height means cold temperatures. Cold upper air temperatures in April are a very good sign of 'potential instability'. We were refering to 'potential instability'. Ofcoarse there is the surface parameters that need to be looked at before deciding wether that instability will be realised.

Hense, YES is the correct answer here.

[TonyT]

Tony, height is strongly correlated to temperature.

A low height means cold temperatures. Cold upper air temperatures in April are a very good sign of 'potential instability'. We were refering to 'potential instability'. Of coarse there is the surface parameters that need to be looked at before deciding wether that instability will be realised.

Hense, YES is the correct answer here.

The map shows 500Hpa height. CNimbus appears to be under the misconception that the blue areas on the map represent cold air and the red areas are warm air. This is incorrect. They are not. They are areas of low and high 500Hpa height.

It would be correct if the map showed temperature or thickness, but it doesnt.

A higher (lower) 500Hpa height indicates a warmer (colder) atmosphere only in the crudest of senses The reason for this is that by looking at the 500 height you are only looking at the top of the layer. (The layer in this case being the bottom half of the atmosphere). In order to ascertain the thickness of the layer, and hence its mean temperature, you need to take into account where the bottom of the layer is as well. (In practice the 1000Hpa height to 500Hpa height).

Certainly the 500Hpa height is higher at the equator (warm layer) and lower at the poles (cold layer) but it could be the same along the length of New Zealand and yet their could be a warm layer over the North ISland and cold layer over the South Island if the surface pressure pattern was such that there was a depression over the North Island and an anticyclone over the south.

An analogy is something like asking about the height of a tree. If you took your measurements with mean sea level as the base then your map of tree height would be as much about the land countour as the height of individual trees. What you need to do is measure the individual tree height above the ground at its base. That way you factor the land contour out of the picture. You need to do the same thing with atmospheric height to get a true picture of (mean layer) temperature.

Having said all that the area of lower height indicated over the South Island does correlate with forecast colder air, and therfore it could well be unstable, but lets get the basics right here and make sure there are no misconceptions. The map doesnt show what it was suggested it did.

[NZstorm]

Tony,

A 500mb trough is good sign of potential instability.

Sure, best way to look at the stability of the atmosphere is to look at the profile of the atmosphere, but the 500mb heights, on there own, do give indications of whats going on in the atmosphere. This chart shows potential instability.

The question was 'Potential Instability?'

Anyway, I think we'll have to agree to disagree.

[TonyT]

Tony,

A 500mb trough is good sign of potential instability.

Agreed. But lets call a trough a trough, not cold air. Or light blue air as in the original post.

This chart shows potential instability.
Anyway, I think we'll have to agree to disagree.

On this point, yes we will.

[NZstorm]

I came across this site which explains the 500mb height and its relationship to temperature nicely.

http://cws.met.psu.edu/members/heights4.htm