On 08/02/12 21:28, Graham P Davis wrote:

"Proper" freezing rain, being super-cooled, will not warm a surface and
may cool it down. This makes it more dangerous for power cables and such
than "normal" rain.


Would there not be a possibility of some warming from the latent heat of
freezing being transferred to the surface?

On Feb 8, 8:01*pm, "Eskimo Will" wrote:
"Alan" wrote in message

...
On Feb 8, 7:25 pm, "Col" wrote:

The local forecast was talking at length about freezing rain
this evening, and how unusual it is, so I am assuming that it
is to be of the genuine 'supercooled' varity, rather than
just 'normal' rain making cold surfaces slippery.

So what makes freezing rain fall at temperatures when
one would normaly expect snow?
--
Col

Bolton, Lancashire
160m asl

Snow will fall if the whole layer of air is sub-zero. But if the snow
hits a layer of air above zero it will start to melt. If this above
zero layer of air is deep enough it will turn the snow completely into
rain. If this rain then hits another layer of sub-zero air, for
instance a surface inversion, it will be cooled. If the surface
inversion is too shallow the rain won’t have a chance to drop below
zero, thus your 'normal' rain making cold surfaces slippery. *If this
sub-zero layer is deep enough the rain’s temperature will have a
chance to drop below zero. Sometimes it will refreeze and give ice
pellets; sometime you will get proper super-cooled rain.
===============================================

Just to add to that excellent explanation that proper freezing rain is when
supercooled rain drops hit a cold surface and freeze instantly on impact.
Freezing rain is also called thus when ordinary rain hits a frozen surface
and freezes after a few minutes. That is what is expected tomorrow.

http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------
*Freezing rain is also called thus when ordinary rain hits a frozen
surface
and freezes after a few minutes.
Not so; this is a common error amongst amateur observers. Freezing
rain must be the result of supercooled water droplets freezing on
impact and it's the "on impact" that's important. Rain which lands on
a below zero surface and "later" freezes is rain, freezing. It's a
subtle but very important difference to proper observers.
Danny.

On Feb 9, 8:58*am, Desperate Dan wrote:
On Feb 8, 8:01*pm, "Eskimo Will" wrote:







"Alan" wrote in message

....
On Feb 8, 7:25 pm, "Col" wrote:

The local forecast wastalking at length about freezing rain thisevening, and how unusual it is, so I amassuming that it
is to be of the genuine 'supercooled' varity, rather than
just 'normal' rain making cold surfaces slippery.

So what makes freezing rain fall at temperatures when
one would normaly expect snow?
--
Col

Bolton, Lancashire 160masl

Snow will fall if the whole layer of air is sub-zero. But if the snow hits a layer of air above zero it will start to melt. Ifthisabove
zero layer of air is deep enough it will turn the snow completely into rain. Ifthisrain then hits anotherlayer of sub-zero air, for
instance a surface inversion, it will be cooled. If the surface
inversion is too shallow the rain won’t have a chance to drop below zero, thus your 'normal' rain making cold surfaces slippery. *Ifthis
sub-zero layer is deep enough the rain’s temperature will have a
chance to drop below zero. Sometimes it will refreeze and give ice
pellets; sometime you will get proper super-cooled rain.
===============================================

Just to add to that excellent explanation that proper freezing rain is when
supercooled rain drops hit a cold surface and freeze instantly on impact.

On Feb 9, 9:20*am, Len Wood wrote:
On Feb 9, 8:58*am, Desperate Dan wrote:









On Feb 8, 8:01*pm, "Eskimo Will" wrote:

"Alan" wrote in message

....
On Feb 8, 7:25 pm, "Col" wrote:

The local forecast wastalking at length about freezing rain thisevening, and how unusual it is, so I amassuming that it
is to be of the genuine 'supercooled' varity, rather than
just 'normal' rain making cold surfaces slippery.

So what makes freezing rain fall at temperatures when
one would normaly expect snow?
--
Col

Bolton, Lancashire 160masl

Snow will fall if the whole layer of air is sub-zero. But if the snow hits a layer of air above zero it will start to melt. Ifthisabove
zero layer of air is deep enough it will turn the snow completely into rain. Ifthisrain then hits anotherlayer of sub-zero air, for
instance a surface inversion, it will be cooled. If the surface
inversion is too shallow the rain won’t have a chance to drop below zero, thus your 'normal' rain making cold surfaces slippery. *Ifthis
sub-zero layer is deep enough the rain’s temperature will have a
chance to drop below zero. Sometimes it will refreeze and give ice
pellets; sometime you will get proper super-cooled rain.
===============================================

Just to add to that excellent explanation that proper freezing rain is when
supercooled rain drops hit a cold surface and freeze instantly on impact.
Freezing rain is also called thus when ordinary rain hits a frozen surface
and freezes after a few minutes. That is what is expected tomorrow.

http://www.lyneside.demon.co.uk/Haytor/automatic/Current_Vantage_Pro.htm Will Hand (Haytor, Devon, 1017 feetasl)
---------------------------------------------

*Freezing rain is also called thus when ordinary rain hits a frozen
surface and freezes after a few minutes.

Not so;thisis a common error amongst amateur observers. Freezing
rain must be the result of supercooled water droplets freezing on
impact and it's the "on impact" that's important. Rain which lands on
a below zero surface and "later" *freezes is rain, freezing. It's a
subtle but very important difference to proper observers.
Danny.

There is a difference as you point out
but
observing it is not always easy.
The 'observer' *has to be out in the rain continuosly looking with an
eagle eye.
Not the case at most stations where they go out every hour on the hour
at most.
Or nearer the truth, never, as many are AWS theses days.
So reporting freezing rain is up to chance.
Assumptions about the rain temperature being sub zero are not always
reliable.
Depends on many things not least the depth of the sub zero layer near
the surface.
Do we have routine obs on this? No. Routine radiosondes do not give
the vertical resolution detail needed near the surface.

So it is often a 'can of worms' for the official as opposed to the
casual observer.

Len Wood
Wembury

I wasn't commenting on the difficulties with observing but on the
definition. I see what your getting at, especially with AWS obs, but I
beg to otherwise disagree. At a Met Office, someone going out every
hour on the hour and ignoring what's gone on in the past hour isn't
observing. Any "proper" observer who only goes out the door once in an
hour, isn't observing. Most observers can tell if there's water over
ice or just ice on surfaces, during precipitation.

On Feb 9, 9:50*am, Desperate Dan wrote:
On Feb 9, 9:20*am, Len Wood wrote:









On Feb 9, 8:58*am, Desperate Dan wrote:

On Feb 8, 8:01*pm, "Eskimo Will" wrote:

"Alan" wrote in message

...
On Feb 8, 7:25 pm, "Col" wrote:

The local forecast wastalking at length about freezing rain thisevening, and how unusual it is, so I amassuming that it
is to be of the genuine 'supercooled' varity, rather than
just 'normal' rain making cold surfaces slippery.

So what makes freezing rain fall at temperatures when
one would normaly expect snow?
--
Col

Bolton, Lancashire 160masl

Snow will fall if the whole layer of air is sub-zero. But if the snow hits a layer of air above zero it will start to melt. Ifthisabove zero layer of air is deep enough it will turn the snow completely into rain. Ifthisrain then hits anotherlayer of sub-zero air, for
instance a surface inversion, it will be cooled. If the surface inversion is too shallow the rain won’t have a chance to drop below zero, thus your 'normal' rain making cold surfaces slippery. *Ifthis
sub-zero layer is deep enough the rain’s temperature will have a
chance to drop below zero. Sometimes it will refreeze and give ice
pellets; sometime you will get proper super-cooled rain.
===============================================

Just to add to that excellent explanation that proper freezing rain is when
supercooled rain drops hit a cold surface and freeze instantly on impact.
Freezing rain is also called thus when ordinary rain hits a frozen surface
and freezes after a few minutes. That is what is expected tomorrow.

http://www.lyneside.demon.co.uk/Haytor/automatic/Current_Vantage_Pro..htm Will Hand (Haytor, Devon, 1017 feetasl)
---------------------------------------------

*Freezing rain is also called thus when ordinary rain hits a frozen
surface and freezes after a few minutes.

Not so;thisis a common error amongst amateur observers. Freezing
rain must be the result of supercooled water droplets freezing on
impact and it's the "on impact" that's important. Rain which lands on
a below zero surface and "later" *freezes is rain, freezing. It's a
subtle but very important difference to proper observers.
Danny.

There is a differenceasyou point out
but observing it is not always easy. The 'observer' *hasto be out in the rain continuosly looking with an
eagle eye. Not the case at most stations where they go out every hour on the hour
at most. Or nearer the truth, never,asmanyareAWS theses days.
So reporting freezing rain is up to chance.Assumptions about the rain temperature being sub zeroarenot always
reliable. Depends on many things not least the depth of the sub zero layer near
the surface. Do we have routine obs onthis? No. Routine radiosondes do not give
the vertical resolution detail needed near the surface.

So it is often a 'can of worms' for the officialasopposed to the casual observer.

Len Wood
Wembury

I wasn't commenting on the difficulties with observing but on the
definition. I see what your getting at, especially with AWS obs, but Ibeg tootherwise disagree. At a Met Office, someone going out everyhour on the hour and ignoring what's gone on in the past hour isn't
observing. Any "proper" observer who only goes out the door once in an
hour, isn't observing. Most observers can tell if there's water over
ice or just ice on surfaces, during precipitation.

It's easier to observe when the rain is much below zero and the
surface is much below zero.
Unfortunately things are often marginal in this country.
Topography plays an important part.
But the UKMO is right to warn the public of the possibilty of ice.
As they are at this moment.

On Feb 9, 10:14*am, Len Wood wrote:
On Feb 9, 9:50*am, Desperate Dan wrote:









On Feb 9, 9:20*am, Len Wood wrote:

On Feb 9, 8:58*am, Desperate Dan wrote:

On Feb 8, 8:01*pm, "Eskimo Will" wrote:

"Alan" wrote in message

...
On Feb 8, 7:25 pm, "Col" wrote:

The local forecast wastalking at length about freezing rain thisevening, and how unusual it is, so I amassuming that it
is to be of the genuine 'supercooled' varity, rather than
just 'normal' rain making cold surfaces slippery.

So what makes freezing rain fall at temperatures when
one would normaly expect snow?
--
Col

Bolton, Lancashire 160masl

Snow will fall if the whole layer of air is sub-zero. But if the snow hits a layer of air above zero it will start to melt. Ifthisabove zero layer of air is deep enough it will turn the snow completely into rain. Ifthisrain then hits anotherlayer of sub-zero air, for
instance a surface inversion, it will be cooled. If the surface inversion is too shallow the rain won’t have a chance to drop below zero, thus your 'normal' rain making cold surfaces slippery. *Ifthis
sub-zero layer is deep enough the rain’s temperature will have a
chance to drop below zero. Sometimes it will refreeze and give ice
pellets; sometime you will get proper super-cooled rain.
===============================================

Just to add to that excellent explanation that proper freezing rain is when
supercooled rain drops hit a cold surface and freeze instantly on impact.
Freezing rain is also called thus when ordinary rain hits a frozen surface
and freezes after a few minutes. That is what is expected tomorrow.

http://www.lyneside.demon.co.uk/Haytor/automatic/Current_Vantage_Pro.htm Will Hand (Haytor, Devon, 1017 feetasl)
---------------------------------------------

*Freezing rain is also called thus when ordinary rain hits a frozen
surface and freezes after a few minutes.

Not so;thisis a common error amongst amateur observers. Freezing
rain must be the result of supercooled water droplets freezing on
impact and it's the "on impact" that's important. Rain which lands on
a below zero surface and "later" *freezes is rain, freezing. It's a
subtle but very important difference to proper observers.
Danny.

There is a differenceasyou point out
but observing it is not always easy. The 'observer' *hasto be out in the rain continuosly looking with an
eagle eye. Not the case at most stations where they go out every hour on the hour
at most. Or nearer the truth, never,asmanyareAWS theses days.
So reporting freezing rain is up to chance.Assumptions about the rain temperature being sub zeroarenot always
reliable. Depends on many things not least the depth of the sub zero layer near
the surface. Do we have routine obs onthis? No. Routine radiosondes do not give
the vertical resolution detail needed near the surface.

So it is often a 'can of worms' for the officialasopposed to the casual observer.

Len Wood
Wembury

I wasn't commenting on the difficulties with observing but on the
definition. I see what your getting at, especially with AWS obs, but Ibeg tootherwise disagree. At a Met Office, someone going out everyhour on the hour and ignoring what's gone on in the past hour isn't
observing. Any "proper" observer who only goes out the door once in an
hour, isn't observing. Most observers can tell if there's water over
ice or just ice on surfaces, during precipitation.

It's easier to observe when the rain is much below zero and the
surface is much below zero.
Unfortunately things are often marginal in this country.
Topography plays *an important part.
But the UKMO is right to warn the public of the possibilty of ice.
As they are at this moment.

I think we can concur on that!

On 09/02/12 00:31, Adam Lea wrote:
On 08/02/12 21:28, Graham P Davis wrote:

"Proper" freezing rain, being super-cooled, will not warm a surface and
may cool it down. This makes it more dangerous for power cables and such
than "normal" rain.


Would there not be a possibility of some warming from the latent heat of
freezing being transferred to the surface?

I think you're right. I had a niggling doubt regarding that when I typed
that comment but decided to go ahead anyway, expecting that Will would
probably correct me. ;-)


--
Graham Davis, Bracknell, Berks. E-mail: change boy to man
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