Frosts in "Sheltered" Areas

NZ Thunderstorm Soc · Sun 11/07/2004 19:11

I wonder about the term 'frosts in sheltered areas'
I thought frosts only occured in open exposed areas???!!!
Where are the 'sheltered' areas that frosts occur?
Could some-ne enlighten me on this

JohnGaul
NZTS

Michael · Unread post by **Michael** » Sun 11/07/2004 20:41

Areas where no wind is

Willoughby · Unread post by **Willoughby** » Mon 12/07/2004 00:06

Are there any particular suburbs in Auckland that will get a frost this morning?

TonyT · Unread post by **TonyT** » Mon 12/07/2004 08:10

Micheal is right - sheltered in this use means sheltered from the wind, not sheltered from the sun/sky.

ricky · Unread post by **ricky** » Mon 12/07/2004 09:23

very light (-0.3 DegC) frost here in Grey Lynn this morning..

NZ Thunderstorm Soc · Mon 12/07/2004 11:46

TonyT wrote:Micheal is right - sheltered in this use means sheltered from the wind, not sheltered from the sun/sky.

Thanks

JohnGaul
NZTS

ScottyD · Unread post by **ScottyD** » Mon 12/07/2004 15:39

There were frosts from at least Albany North as I drove up to Silverdale this morning. Didn't seem too severe, but good to hear that cruching under the feet. Haven't heard that for a long time up in Auckland.

Manukau heads obs · Mon 12/07/2004 15:56

basins/vallyes get frosts much easier....the cold air sinks.....but hill tops/steep hill slopes miss out.....thats why alot of the auckland city area misses out...becuase of the hills....the air is always moving down/down around them.,....but also, its not far from the water in the auckland isthmus ....and the water does not get as cold as the land at night, and so moderates the temperature.....
there have been frosts in the dargaville/brynderwen area, which is the southern part of northland...
see:
http://ps.gen.nz/~richkids/brynderwyn.htm

anyway, just my thoughts and ramblings...

Michael · Unread post by **Michael** » Mon 12/07/2004 16:12

I always *most* times we get a breeze of some kind in Auckland,It is hardly ever dead still like ie Christchurch in a WSW or Wanganui in a NE for instance

NZstorm · Unread post by **NZstorm** » Mon 12/07/2004 18:58

I didn't notice any frost here this morning. Some years we get a frost or two, other years we don't.

Another factor governing frost in the Auckland area is the urban heat Island. Urban heat island protects the CBD area from frost. Temperature difference between the CBD and environs can be as much as 6C at night, typically 3-4C.

spwill · Unread post by **spwill** » Mon 12/07/2004 19:38

First frost of the year here this morning. Open grass areas + car roofs, windscreens were white. I think last year we got 3 frosts here.

ricky · Unread post by **ricky** » Mon 12/07/2004 19:46

was definitely white and crunchy Steven

and a probe in the grass showed -0.3C in one of the lighter areas.. maybe this side of the grey lynn ridge was a bit more sheltered? air temp got down to 2.0C at approx 1.2m above ground

NZstorm · Unread post by **NZstorm** » Mon 12/07/2004 20:34

Ricky wrote

was definitely white and crunchy Steven

We seem to have missed that frost on Archhill. I'm on a south facing slope, your a north facing slope. There was a slight southerly drift this morning.

Michael · Unread post by **Michael** » Mon 12/07/2004 21:09

I prefer frosts to gales/rain though

tich · Unread post by **tich** » Mon 12/07/2004 21:57

Another factor governing frost in the Auckland area is the urban heat Island. Urban heat island protects the CBD area from frost. Temperature difference between the CBD and environs can be as much as 6C at night, typically 3-4C.

A similar heat island effect operates in Chch, but here it means that frosts are lighter than in the outer parts of the city and especially the adjacent countryside. Chch's CBD certainly isn't frost free.

Willoughby · Unread post by **Willoughby** » Mon 12/07/2004 22:55

On that note, why is Hamilton relatively frosty? (-4c yesterday morning...) Does the basin effect us?
0c right now

Our CBD is very frosty, hence the buildings are spreadout more?

Gary Roberts · Unread post by **Gary Roberts** » Tue 13/07/2004 00:14

Foggy Hamilton wrote:On that note, why is Hamilton relatively frosty? (-4c yesterday morning...) Does the basin effect us?
0c right now
Our CBD is very frosty, hence the buildings are spreadout more?

Midnight and it's -4.3Â° here in Omarama...it'll get a bit colder than that just before sunrise. I'm expecting a good frost today!

Manukau heads obs · Tue 13/07/2004 06:39

hamilton is inland, away from the oceans, which moderate the temperature, so you couple that with also being in a large area of relatively flat land too

(i.e the ground surface quickly radiates heat away into space)

where I am living now, on the NE tip of the awhitu peninsular, we are not geting frosts...the temperature is not going much below 5oC
and yet Waiuku and Pukekohe and even lower lying vallyes and basins near me are....i.e we are on top of a hill here, you see...
just me rambling again

NZstorm · Unread post by **NZstorm** » Tue 13/07/2004 07:31

Clear here this morning with 5C. No Frost.

Re Hamilton's urban heat island. There will be one, but will be relatively weak. And as Brian points out, Hamilton has the geography for a frosty climate.

Manukau heads obs · Tue 13/07/2004 07:46

4.6oC here, and still dropping....as cloud on the eastern horizon is stopping the sun....
actualy, often, the coldest part of the morning is just after sunrise, as it takes a 15,30 minutes before there is enough heating from the sun to counteract the loss of heat to space....after sunrise....
but at high altitudes, with the sun doing a long slow climb, it wil be much longer before that happens....
just an interesting observation (i.e i have seen it near matamata that the puddles acutaly froze in sun shaded areas quite a while after the sun got up (when they were not frozen before the sun rise (i was helping milk cows , LOL))

spwill · Unread post by **spwill** » Tue 13/07/2004 08:34

Another light frost here this morning.

Peter · Unread post by **Peter** » Tue 13/07/2004 08:56

Heavy frost here in Pt Chevalier - cars all covered in white, roofs frosty, and some ice on shallow pools of water - 2nd day running, must be much cooler here than Grey Lynn

Gary Roberts · Unread post by **Gary Roberts** » Tue 13/07/2004 11:18

At 06:19 it was -6.2Â° in Omarama. Another cloudless day. No winter for us this year it seems.

NZ Thunderstorm Soc · Tue 13/07/2004 18:07

No frost here this morning, not even in any 'sheltered area'. I got down to 5.8C in cloudy conditions

JohnGaul
NZTS

Andy · Unread post by **Andy** » Tue 13/07/2004 18:34

yea clear skies - big frost -8 here