A Strange Frost Tonight

[Backtrack]

Hi guys.

Tonight the temperature has been hovering around 4 to 6C, with it been sat on 4.9C for a while now.

Yet I've just taken the dog, and some of the newer cars have frost on the top with a frozen windscreen, and there's also frost on the grass.

I know that metal loses its heat much quicker than the ground, and that's going to be below zero, but why is it frozen when the temperature is about 5C? Surely the temperature of the grass/metal can't be 5C below the air temperature can it?

Or do you think my sensor is out a little?

Thanks.

[Liam J]

I think your sensor is out alot BT!! The air temp would have to be 0c for cars to freeze.

[Backtrack]

I think your sensor is out alot BT!! The air temp would have to be 0c for cars to freeze.

Only the roofs of the cars, and part of the back windscreen on a couple.

[Liam J]

Only the roofs of the cars, and part of the back windscreen on a couple.

If frost is forming on cars then the air temp is @ 0c max

It's 1.9c here with no frost yet, just heavy dew.

looking around your area most readings are +2-5c

Edited November 6, 2011 by Liam J

[Backtrack]

If frost is forming on cars then the air temp is @ 0c max

It's 1.9c here with no frost yet, just heavy dew

Remember though that surfaces such as metal lose their heat much much faster than anything else does, it can be well above 0C for a car frost. I was just a little skeptical about the whole 4.9C frozen thing.

[Aaron]

You can see frost on car roofs at air temperatures above 0C. Frost can certainly occur at temperatures as high as 4 -5C

Edited November 6, 2011 by Aaron

[Isolated Frost]

Batteries are messed up mate

[johnholmes]

The air temp would have to be 0c for cars to freeze.

that is not correct for frost to form on grass=ground frost not air frost, also frost on cars does not require an air temperature of 0C.

[Paul]

In fact cars freeze faster than most other things as metal radiates heat more quickly than the majority of other surfaces so therefore will often be colder than the ground.

[Snowstorm1]

In fact cars freeze faster than most other things as metal radiates heat more quickly than the majority of other surfaces so therefore will often be colder than the ground.

This helps explain why snow lays on cars easier than the ground

[johnholmes]

In fact cars freeze faster than most other things as metal radiates heat more quickly than the majority of other surfaces so therefore will often be colder than the ground.

yep, correct and good explanation for those wondering why it occurs

[Isolated Frost]

Yep ss1- good little physics lesson from paul there haha!

[SP1986]

It's quite a strange night around here too, there's fairly consistent breeze right now, and given the relative warmth of the atmosphere, a breeze would normally mean a rise in temperatures, especially on coastal hill top, however it just keeps dropping. Very unusual indeed, I've never known the temperature to keep dropping with a breeze in this location. Very unusual!

[Snowstorm1]

Yep ss1- good little physics lesson from paul there haha!

Yep considering in September I started my AS Physics course any snippets of information are helpful

[Backtrack]

In fact cars freeze faster than most other things as metal radiates heat more quickly than the majority of other surfaces so therefore will often be colder than the ground.

So would it be safe to conclude that my temperature is correct? Hovering just above 4C now.

Edited November 6, 2011 by Backtrack

[Liam J]

that is not correct for frost to form on grass=ground frost not air frost, also frost on cars does not require an air temperature of 0C.

I never mentioned ground frost, I have seen many times a frost on the ground when the temp has been around 1-3c, the ground can be much colder than the air temp above say at a 2m height.

I'm sorry but I don't believe for 1 second that the cars were frozen @ +5c

+1.7c here with no frozen cars

Edited November 6, 2011 by Liam J

[Backtrack]

I never mentioned ground frost, I have seen many times a frost on the ground when the temp has been around 1-3c, the ground can much colder than the air temp above say at a 2m height.

I'm sorry but I don't believe for 1 second that the cars were frozen @ 5c

Do I REALLY have to go outside and take a picture of someone's car like a weirdo?

[johnholmes]

I never mentioned ground frost, I have seen many times a frost on the ground when the temp has been around 1-3c, the ground can much colder than the air temp above say at a 2m height.

I'm sorry but I don't believe for 1 second that the cars were frozen @ +5c

+1.7c here with no frozen cars

I never said you mentioned ground frost, I posted the comment to illustrate how frost can occur on grass(ground frost) or cars(same or very similar thing) as the ground and cars(see post from Paul) do often radiate faster than the air at Stevenson screen level.

That is why Met, especially early and late in the season differentiate between the two. Its quite important that the threat of ground frost is mentioned for market gardeners etc.

[bobbydog]

this one's got me wondering now, - if the ambient temperature is 5c, even allowing for metal cooling quicker, surely the cars would be also 5c. if water freezes at 0c, how does this frost or ice, (which is obviously frozen water) occur?

[AderynCoch]

Car frost here for what it's worth.

[johnholmes]

this one's got me wondering now, - if the ambient temperature is 5c, even allowing for metal cooling quicker, surely the cars would be also 5c. if water freezes at 0c, how does this frost or ice, (which is obviously frozen water) occur?

not the surface of the car, also interesting that cars of different colours will form frost at different times on the same night

[Backtrack]

not the surface of the car, also interesting that cars of different colours will form frost at different times on the same night

Mostly the darker coloured cars have the frost on here.

[Liam J]

Strange things happen in Runcorn, anyone else have frozen cars atm and a temp of +5c?

I can say I have never witnessed vehicles freezing when the temp has been that high.

Other factors must have an affect here, what is your Dew point and Humidity?

Here - temp +1.7c DP 0.2c and humidity 94% with no frost on my dark red car or next doors black car.

Edited November 6, 2011 by Liam J

[bobbydog]

not the surface of the car, also interesting that cars of different colours will form frost at different times on the same night

i realise that darker colours radiate heat faster, (actually having thought about it, lighter colours, or metallic silver may even reflect heat during the day allowing them to have less heat retained in them by the time it cools down!) but i don't get how something can be colder than the ambient temperature, enough to reach freezing point. maybe you could explain that to me sometime (when you have the time) as it's really caught my interest!

Edited November 6, 2011 by bobbydog

[Backtrack]

Strange things happen in Runcorn, anyone else have frozen cars atm and a temp of +5c?

I can say I have never witnessed vehicles freezing when the temp has been that high.

Other factors must have an affect here, what is your Dew point and Humidity?

Here - temp +1.7c DP 0.2c and humidity 94% with no frost on my dark red car or next doors black car.

I can't answer that, my more technical station is out of order due to me failing to change the batteries on the roof. Mainly due to me having no batteries.

I'm relying on my Science Museum weather station, which has ALWAYS been as accurate as my main WS.