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That's what I'm talking about. I think it's really just down to high pressure producing very calm conditions.
The episode that just happened here was quite a weak one, due to temperatures reaching 15C towards the end, but it was still enough for the frost to grow at maximums between 10C and 13.5C.
The best one I can remember was in July 2001, when the temperature dropped to -5.8C, but days were between 9C and 12C. Frost was growing in the shade even right on the beach and got very thick indeed. A feature of that cold spell was some of the workers where I was, getting light sunburns -quite peculiar weather. Lasted about 10 days.
Even the July 2001 spell has milder daytime highs than Paris' Dec 2013 spell. I don't think frost would last with days between 9°C and 12°C, definitely not between 10°C and 13.5°C. Though it's hard to compare, as we normally get smaller diurnal ranges and a week with hard freezes and maxes in the low teens Celsius would be unusual apart from maybe March. Would need to ask someone who lives in a frost hollow.
Quote:
Originally Posted by nei
Huh. Still puzzled how frost could survive mild midday temperatures. Frost is always something I think is fleeting; though I haven't checked shaded areas carefully. Hard frost in October:
at 8 am or so, can't imagine any of it lasting past midday.
Maybe the lower sun at 49°N compared to 43°N makes it easier for cold air pools in low-lying, shaded areas to last all day long? The sun feels weaker in December in Paris compared to Nice.
Even the July 2001 spell has milder daytime highs than Paris' Dec 2013 spell. I don't think frost would last with days between 9°C and 12°C, definitely not between 10°C and 13.5°C. Though it's hard to compare, as we normally get smaller diurnal ranges and a week with hard freezes and maxes in the low teens Celsius would be unusual apart from maybe March. Would need to ask someone who lives in a frost hollow.
Finally found the figures for the July 2001 cold spell, not for Motueka unfortunately, but Appleby, which is the next official station along. Quite a chilly one as you can see - it doesn't show the grass (ground) temperature, but from memory, the coldest nights were around -12C/-13C.
There was absolutely frost on the ground, in shaded areas, for over a week ... right on the beach even -it was a big talking point at the time. I understand the skepticism over frost on the ground at temperatures above 13.5C, but frost at temperatures between 9-12C is normal, and I'm not talking about that. This area is one big frost hollow.
The second chart shows the Motueka temperatures during the recent spell, pretty minor in comparison, but it does give an idea between air and grass minimums.
There was absolutely frost on the ground, in shaded areas, for over a week ... right on the beach even -it was a big talking point at the time. I understand the skepticism over frost on the ground at temperatures above 13.5C, but frost at temperatures between 9-12C is normal, and I'm not talking about that. This area is one big frost hollow.
Again, just because it's normal in New Zealand does not mean it is normal elsewhere. You make comments about seeing frosts rather frequently, more so than most posters here, good indication your location isn't a good to base "normal" from.
Looking at your temperatures, that combination is something that occurs late March/April when the sun is much higher or about in November, when the soil temperature would be fairly warm. I'd like to find a site that records ground temperature, not sure if US weather stations do so.
Again, just because it's normal in New Zealand does not mean it is normal elsewhere. You make comments about seeing frosts rather frequently, more so than most posters here, good indication your location isn't a good to base "normal" from.
Looking at your temperatures, that combination is something that occurs late March/April when the sun is much higher or about in November, when the soil temperature would be fairly warm. I'd like to find a site that records ground temperature, not sure if US weather stations do so.
It's not a matter of it being normal, or not - I know that in parts of NZ, it wouldn't be normal, while in many parts of the world, it would be normal. What I meant, was that the frost remaining at temperatures of 9-12C , is normal for here.
I didn't expect much response from European posters , as I don't think the conditions really exist there for it to happen much.
I had expected more response from North American posters, as the conditions would be more similar to here. It doesn't seem like many posters pay much attention to frost though.
Used to be that people would talk about weather on this forum, now it's just charts, and "what is your favourite chip flavour?"
I've notice that too. But then again most people type on smartphones these days and you can't post long replies or topics on those tiny keys so long weather/climate discussions that lasts for page 5+ are no go. Big industry wants us to think they are as good as computers but in reality for many reasons more then the keyboard problem they are not.
Windows 8 and 10 actually have very different coding catered to mobile users only in the BIOS languages not just looks or interface as part of the push to get users to dump the PC and go for the phone.
As for frost at warm temperatures. I have seen frost at 37F degrees and in shaded areas at 45F.
Frost stayed all day long on north-facing roofs today with a high around 7°C. Made me think of this thread.
Interesting. Frost doen't stay on roofs here, although at clear day below 10C is rare - more likely to get those temperatures on a rainy day.
Any idea what the air minimum and ground minimum were? Was there a visible ground frost there this morning? I'm wondering if some places don't see visible ground frost as often (and therefore no lingering frost) because the dew points and diurnal range aren't as high.
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