The grand daughter insists there was a thin film of ice on the car
windscreen this morning. It was certainly pretty chilly but did anyone
else see this in UK? In the balmy SW it seems a bit early!
--
Sacha
www.hillhousenursery.com
Shrubs & perennials. Tender & exotics.
South Devon

On Mon, 21 Sep 2009 13:17:06 +0100, Sacha wrote:

The grand daughter insists there was a thin film of ice on the car
windscreen this morning. It was certainly pretty chilly but did anyone
else see this in UK? In the balmy SW it seems a bit early!

No. She's a liar and not to be trusted. She takes after you.

In article ,
says...
The grand daughter insists there was a thin film of ice on the car
windscreen this morning. It was certainly pretty chilly but did anyone
else see this in UK? In the balmy SW it seems a bit early!

We have had a couple of grass frosts, the Gunnera is black
--
Charlie Pridham, Gardening in Cornwall
www.roselandhouse.co.uk
Holders of national collections of Clematis viticella cultivars and
Lapageria rosea

Charlie Pridham writes
In article ,
says...
The grand daughter insists there was a thin film of ice on the car
windscreen this morning. It was certainly pretty chilly but did anyone
else see this in UK? In the balmy SW it seems a bit early!

We have had a couple of grass frosts, the Gunnera is black

What is a grass frost? It's a term I hadn't heard till this year, when
it's been sneaking into all the weather forecasts. And how does it
compare with a ground frost or an air frost? And how do any of these
compare with a temperature of 0 deg C (since the weather forecast is
fond of announce that there will be night time temperatures of, say, 2
deg C and therefore we can expect a frost)
--
Kay

In article ,
K wrote:

What is a grass frost? It's a term I hadn't heard till this year, when
it's been sneaking into all the weather forecasts. And how does it
compare with a ground frost or an air frost? And how do any of these
compare with a temperature of 0 deg C (since the weather forecast is
fond of announce that there will be night time temperatures of, say, 2
deg C and therefore we can expect a frost)

I think that a grass frost and ground frost are the same thing, and
an air frost is a temperature below 0 Celsius.


Regards,
Nick Maclaren.

writes
In article ,
K wrote:

What is a grass frost? It's a term I hadn't heard till this year, when
it's been sneaking into all the weather forecasts. And how does it
compare with a ground frost or an air frost? And how do any of these
compare with a temperature of 0 deg C (since the weather forecast is
fond of announce that there will be night time temperatures of, say, 2
deg C and therefore we can expect a frost)

I think that a grass frost and ground frost are the same thing, and
an air frost is a temperature below 0 Celsius.


and a ground frost is warmer than an air frost?
--
Kay

In article ,
K wrote:

I think that a grass frost and ground frost are the same thing, and
an air frost is a temperature below 0 Celsius.

and a ground frost is warmer than an air frost?

Yes. The exact difference depends on how clear the sky/air is.


Regards,
Nick Maclaren.

In message ,
writes
In article ,
K wrote:

What is a grass frost? It's a term I hadn't heard till this year, when
it's been sneaking into all the weather forecasts. And how does it
compare with a ground frost or an air frost? And how do any of these
compare with a temperature of 0 deg C (since the weather forecast is
fond of announce that there will be night time temperatures of, say, 2
deg C and therefore we can expect a frost)

I think that a grass frost and ground frost are the same thing, and
an air frost is a temperature below 0 Celsius.

An air frost is when the temperature of the air falls below 0 Celsius.
Because of cooling by radiation, and the relatively low heat capacity
and conductivity of air, at night the temperature of the surface of the
ground can fall below that of the air above it. This is a ground or
grass frost.


Regards,
Nick Maclaren.

--
Stewart Robert Hinsley

Stewart Robert Hinsley writes
In message ,
writes
In article ,
K wrote:

What is a grass frost? It's a term I hadn't heard till this year, when
it's been sneaking into all the weather forecasts. And how does it
compare with a ground frost or an air frost? And how do any of these
compare with a temperature of 0 deg C (since the weather forecast is
fond of announce that there will be night time temperatures of, say, 2
deg C and therefore we can expect a frost)

I think that a grass frost and ground frost are the same thing, and
an air frost is a temperature below 0 Celsius.

An air frost is when the temperature of the air falls below 0 Celsius.
Because of cooling by radiation, and the relatively low heat capacity
and conductivity of air, at night the temperature of the surface of the
ground can fall below that of the air above it. This is a ground or
grass frost.

Thanks, and to Nick
--
Kay

On 2009-09-21 14:14:17 +0100, Charlie Pridham
said:

In article ,
says...
The grand daughter insists there was a thin film of ice on the car
windscreen this morning. It was certainly pretty chilly but did anyone
else see this in UK? In the balmy SW it seems a bit early!

We have had a couple of grass frosts, the Gunnera is black

Good heavens! And the grand daughter lives less than 2 minutes away.
We have tree canopy here which helps in different parts of the garden
but this is sounding quite strange.
--
Sacha
www.hillhousenursery.com
Shrubs & perennials. Tender & exotics.
South Devon

Air frost
When the temperature in the Stephenson screen reaches zero, there is said to
be an 'air frost'. Even with an air frost, the ground can sometimes stay
above freezing. This often happens in early autumn, when the soil still
retains some of its Summer heat. Normally though the temperature at ground
level will be significantly colder!

Ground frost
Sometimes the air temperature at night dips to 3 or 4 degrees, but the
forecaster still warns of a 'ground frost' and the need to de-ice your car
in the morning. This is because the ground can reach freezing while the air
temperature remains above.

Hoar frost
The white crystals seen on the grass on a cold morning are neither a ground
nor an air frost. This is a 'hoar frost', which forms when the air cools and
water condenses onto the grass.



Taken from http://www.bbc.co.uk/weather/feature...ng/frost.shtml

Hoar Frost = Grass Frost.

jim, Northampton

In article ,
jbm wrote:

Hoar frost
The white crystals seen on the grass on a cold morning are neither a ground
nor an air frost. This is a 'hoar frost', which forms when the air cools and
water condenses onto the grass.

Interestingly enough, in the UK, that is 70% wrong. Most of the
condensation (and hence hoar frost) is water that evaporates from
the ground and condenses onto the grass.


Regards,
Nick Maclaren.

On 2009-09-21 23:07:44 +0100, "jbm" said:

Air frost
When the temperature in the Stephenson screen reaches zero, there is said to
be an 'air frost'. Even with an air frost, the ground can sometimes stay
above freezing. This often happens in early autumn, when the soil still
retains some of its Summer heat. Normally though the temperature at ground
level will be significantly colder!

Ground frost
Sometimes the air temperature at night dips to 3 or 4 degrees, but the
forecaster still warns of a 'ground frost' and the need to de-ice your car
in the morning. This is because the ground can reach freezing while the air
temperature remains above.

Hoar frost
The white crystals seen on the grass on a cold morning are neither a ground
nor an air frost. This is a 'hoar frost', which forms when the air cools and
water condenses onto the grass.



Taken from http://www.bbc.co.uk/weather/feature...ng/frost.shtml

Hoar Frost = Grass Frost.

jim, Northampton

Thank you! I'm going to bookmark that.
--
Sacha

It is the same as the way on a sunny day the sun can heat your car so that it is so hot you can't touch it, though the air temperature may be only 20C or so. Likewise, the entire black night sky is a source of cold (just like the sun is a source of heat) that can cool the ground, or your car, to below the temperature of the air, though the effect is typically not as powerful as for the sun. I think typically your car windscreen frosts over before hoar forms on the grass. One term for this is "radiative frost", as the cold comes from radiation from the sky, as opposed to "convective frost", where the cold is communicated by convection (ie movement) of the air.

Reducing radiative frost is why plants with overhanging evergreen branches can survive the winter much better than those that can "see" the whole black sky. One of the beneficial effects of being against a wall, as opposed to an open situation, is that it reduces the amount of black sky the plant can "see".

"echinosum" wrote in message
...

'jbm[_2_ Wrote:
;865058']Ground frost
Sometimes the air temperature at night dips to 3 or 4 degrees, but the

forecaster still warns of a 'ground frost' and the need to de-ice your
car
in the morning. This is because the ground can reach freezing while the
air
temperature remains above.

It is the same as the way on a sunny day the sun can heat your car so
that it is so hot you can't touch it, though the air temperature may be
only 20C or so. Likewise, the entire black night sky is a source of
cold (just like the sun is a source of heat) that can cool the ground,
or your car, to below the temperature of the air, though the effect is
typically not as powerful as for the sun. I think typically your car
windscreen frosts over before hoar forms on the grass. One term for
this is "radiative frost", as the cold comes from radiation from the
sky, as opposed to "convective frost", where the cold is communicated
by convection (ie movement) of the air.

Reducing radiative frost is why plants with overhanging evergreen
branches can survive the winter much better than those that can "see"
the whole black sky. One of the beneficial effects of being against a
wall, as opposed to an open situation, is that it reduces the amount of
black sky the plant can "see".

Oh my! The things you learn here!!