Frosts in October?

[gopolks]

Last week was freaky.

[NZstorm]

The -3C 7am temperature at Christchurch Airport on Friday morning caught my eye. I don't know what the exact minimum temperature recorded at CH airport was but I had a flick through the October records for the last 15 years. A temperature of -3C has only happened once before since 1995, -3.3C October 2002.

[NZ Thunderstorm Soc]

Last week was freaky.

Why?

JohnGaul
NZTS

[CHCH Weather Chaser]

That day was interesting actually (the day im talking about with the -3 degrees recorded at the airport) . The reason i say this was because i had newstalk ZB on at the time and Ken Ellis said that it was -3 at the airport and 6 degrees in the city centre! 9 degrees difference. Thats amazing! Thats weather for ya!!

[NZstorm]

Yes the warmer central city temperature was the urban heat Island effect.

[Gary McConnochie]

I find that temperature hard to believe. I recorded 0.5C that day. Big variance between temps in a very short distance. I dont have any "urban heat island effect" where I live either as far as I know.

[NZstorm]

I agree that the -3C is a bit of an out lier but the CH Airport is quite a reliable weather station.
Urban heat Islands tend to mostly affect the intensely built up areas of a central city. The other warming factor in CH is the coast.

[Nev]

The -3C 7am temperature at Christchurch Airport on Friday morning caught my eye. I don't know what the exact minimum temperature recorded at CH airport was but I had a flick through the October records for the last 15 years. A temperature of -3C has only happened once before since 1995, -3.3C October 2002.

You missed Oct 19 last year. But yes, Friday was only the 6th time Chch Aero has recorded -3.0°C or below for October in its 65 year history.

2008 Oct 10 .. -3.0
2007 Oct 19 .. -3.0
2002 Oct 15 .. -3.3
1994 Oct 03 .. -3.6
1987 Oct 16 .. -2.9
1976 Oct 05 .. -4.2
1954 Oct 16 .. -4.1

Most years Chch Aero will record either 0, 1 or 2 frost days in Oct. Interestingly, the only years with more than 2 frost days since 1965, i.e. 2007, 2003, 2002, 1994, 1976 and 1954, all recorded 5 days of frost except for 2002, which recorded 6.

[RWood]

I can help here - the 30-year mean Oct min. for Chch Gardens is 7.2C, Aero values is 6.3C (the annual average difference is similar at 0.8C).

[Nev]

Yes, temps about 2-3 degrees warmer at Chch Gardens for those dates posted above.

[Ryan Thomas]

I wish they'd change the official station to the garden then if they difference is that big. And I think Jeffs wasn't to cold that morning, cause I remember checking Metservice one day and seeing -3 as the low for the previous day and I was like what?? I can't remember it even being close to that cold overnight at Jeffs. Huge difference.

[Manukau heads obs]

you are never going to get one shoe size fits all
i.e there are lots of microclimates in any given area
i.e alot of places would be different to either the Garden or Jeffs place in and around the various mircoclimate ares of CHCH