Pocket of very dry air through Auckland?

[ricky]

Has anyone else noticed the massive and brief drop in Dew Point over the last hour or so?
Here in Grey Lynn it dropped from around 15º to a brief low of 0º , 18% RH and is now back up to 1º
Metservice Whenuapai shows similar brief drops to about 5 degrees as does Waiheke and Whangparaoa but out West and SouthEast of here hardly any change at all..
DP has been very jumpy all afternoon but be interesting to know where this very dry air in the mix originated!

[David]

I thought that was your humidity sensor playing up?

Lowest humidity here today has been 47%. If that 18% reading is correct that must be some sort of record. I have never recorded a humidity below about 35%.

[Manukau heads obs]

the key here David is that Ricky has found other sites with similar big dips in the dew point

there is a easterly change moving through the BOP (looks like a shockwave on the sat image!)
so maybe this pocket of dry air has run ahead of that ?

[David]

the key here David is that Ricky has found other sites with similar big dips in the dew point

Yeah I'm not suggesting his sensor is faulty - that's just what I thought when I saw a reading of 24% earlier - and none of the other sites I looked at showed a dip. Clearly if other sites have picked it up, something very interesting has gone on!

It's strange - the airport to the South didn't get it, me out east didn't get it

[ricky]

Yes I thought it could be a fault when i first saw it too. But yeah same thing does show up elsewhere, not quite as pronounced, but that may be because of the fan aspiration here which lets it react very quickly to changes and the really low readings did only last a couple of minutes..

[NZstorm]

I saw the reading of 7.5C too and thought it a bit odd. But then we have light winds and clear skies and I thought it would be dry air mixing down due to convective turbulence.

[Manukau heads obs]

dry air mixing down due to convective turbulence

ohhh, nice......sounds very plausible
good one NZstorm, I knew someone here would know an explanation

I thought it must have been related to the local heating Ricky was getting at that time

[ricky]

did see a bit of wind variation around that, no sudden temp changes but it was increasing.. sounding does show very dry warm air with a low boundary ~ 950m so that could be it

[David]

did see a bit of wind variation around that, no sudden temp changes but it was increasing.. sounding does show very dry warm air with a low boundary ~ 950m so that could be it

Did you go outside to see dry how it felt? 16% humidity must be a once in a lifetime thing in Auckland?

[ricky]

yeah we were outside at the time, and it was very pleasant!
great looking graphs for the day...

[Nev]

Interesting phenomenon! Not so noticeable here on Waiheke, but below are few more nearby graphs from Wunderground. Almost looks like that pocket of dry air is moving from west to east?

Note that some of these figures aren't necessarily accurate, but it does show the trend...

Code: Select all

T-max   DP-min  Site (Jan 8)
27.2C   -1.9C   Avondale 
24.9C    9.3C   Mt Roskill 
26.8C   -2.0C   Grey Lynn 
29.2C    8.3C   Mission Bay 
28.4C   11.9C   St Heliers Bay 
28.5C    9.1C   Stanley Point 
32.7C   -6.7C   Birkenhead
32.6C    8.9C   Bayview 

[NZstorm]

The NZWP sounding showed astonishingly dry air at low levels with a dp of -20C at 1000m. I find it very hard to believe but thats what was observed. The very dry air had lifted to above 1500m by the midnight sounding.

Yesterdays midday sounding.

[ricky]

Interesting Graphs Nev, I did notice the wind flicking more to the West around that time, but very little change in temp