Hello

I was watching some of the snow reports coming in tonight when I realised I did not know the answer to the following question:
Does Snow turn to Sleet as a rule before becoming rain as one returns to sea level from a snowy higher area?

Thank you

Barry Horton

www.afour.demon.co.uk

"Barry Horton" wrote in message ...
Hello

I was watching some of the snow reports coming in tonight when I realised I did not know the answer to the following question:
Does Snow turn to Sleet as a rule before becoming rain as one returns to sea level from a snowy higher area?

Thank you

Barry Horton

www.afour.demon.co.uk

Hi Barry,

Yes it normally does. Sleet is rain and snow mixed together as some flakes have melted. Driving home today from sea level I went through an area of sleet, but only for 50 metres upwards. The zone of sleet depends on the atmospheric profile, if it is near isothermal then sleet can exist in quite a thick slab of atmosphere.

Will
--

--
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

On Sun, 29 Jan 2012 20:49:24 -0000, Barry Horton wrote:

Something only in HTML...

Does Snow turn to Sleet as a rule before becoming rain as one returns to
sea level from a snowy higher area?

Yes, sleet is snow that has partially melted. This normally happens
in a fairly narrow band, around here full on snow to just rain
happens within a 200' or less vertical band.

--
Cheers Dave.
Nr Garrigill, Cumbria. 421m ASL.

On 29/01/2012 20:49, Barry Horton wrote:
Hello
I was watching some of the snow reports coming in tonight when I
realised I did not know the answer to the following question:

Does Snow turn to Sleet as a rule before becoming rain as one returns
to sea level from a snowy higher area?

Thank you

Barry Horton

www.afour.demon.co.uk http://www.afour.demon.co.uk


If by "sleet" we mean the British usage of partly melted snow or mixed
rain and snow, then the answer is "yes". There has to be a zone during
which the snow is melting. The snow takes time to melt and will fall a
distance under gravity during this time. This zone may be shallower or
deeper depending on the temperature and humidity structure of the
atmosphere.

The melting of the snow will remove from the air the "latent heat"
required to change water from the solid to liquid state and so heavy
falling snow will force the freezing level down and allow the snow to
reach lower levels.

If the air is dry, further cooling by evaporation will also allow the
snow to reach lower levels. In dry enough conditions, snow can reach
the ground when the air temperature is several degrees above freezing.
Conversely, when humidities are high, snow will melt more rapidly and
unless precipitation rates are high, will not reach levels more than a
degree or two above freezing.

Occasionally, another layer of very cold air can exist near the ground
so snow melts to rain and then falls into sub-zero air temperatures.
This will result in the rain becoming "supercooled" (depending on the
drop size, water in droplet form can exist as liquid at temperatures
below freezing - this can be several tens of degrees below freezing for
very small droplets). This supercooled rain will freeze on contact with
any sub-zero surface, resulting in "glazed frost" or "ice storm"
conditions. This is arguably the worst and most destructive form of
winter precipitation we see and is particularly damaging in parts of the
USA although we do occasionally get these conditions here. An "ice
storm" can render roads almost totally undriveable (and pavements
unwalkable, for that matter) in minutes and a prolonged one will coat
tree branches and power lines with enough ice to bring them down,
resulting in widespread damage and power outages.

If the cold air layer below the rain is cold enough and deep enough the
raindrops will partly or wholly re-freeze to ice before reaching the
ground. This is what our American cousins call "sleet".

--
- Yokel -

Yokel posts via a spam-trap account which is not read.

Hello Yokel
Thank you for your very full and detailed answer.

Which ever way one looks at it we only have light, fine, intermittent rain
here in Bristol at the present time 21:23GMT at 3.0C

Barry

www.afour.demon.co.uk

"Yokel" wrote in message
...
On 29/01/2012 20:49, Barry Horton wrote:
Hello
I was watching some of the snow reports coming in tonight when I realised
I did not know the answer to the following question:

Does Snow turn to Sleet as a rule before becoming rain as one returns to
sea level from a snowy higher area?

Thank you

Barry Horton

www.afour.demon.co.uk http://www.afour.demon.co.uk


If by "sleet" we mean the British usage of partly melted snow or mixed
rain and snow, then the answer is "yes". There has to be a zone during
which the snow is melting. The snow takes time to melt and will fall a
distance under gravity during this time. This zone may be shallower or
deeper depending on the temperature and humidity structure of the
atmosphere.

The melting of the snow will remove from the air the "latent heat"
required to change water from the solid to liquid state and so heavy
falling snow will force the freezing level down and allow the snow to
reach lower levels.

If the air is dry, further cooling by evaporation will also allow the snow
to reach lower levels. In dry enough conditions, snow can reach the
ground when the air temperature is several degrees above freezing.
Conversely, when humidities are high, snow will melt more rapidly and
unless precipitation rates are high, will not reach levels more than a
degree or two above freezing.

Occasionally, another layer of very cold air can exist near the ground so
snow melts to rain and then falls into sub-zero air temperatures. This
will result in the rain becoming "supercooled" (depending on the drop
size, water in droplet form can exist as liquid at temperatures below
freezing - this can be several tens of degrees below freezing for very
small droplets). This supercooled rain will freeze on contact with any
sub-zero surface, resulting in "glazed frost" or "ice storm" conditions.
This is arguably the worst and most destructive form of winter
precipitation we see and is particularly damaging in parts of the USA
although we do occasionally get these conditions here. An "ice storm" can
render roads almost totally undriveable (and pavements unwalkable, for
that matter) in minutes and a prolonged one will coat tree branches and
power lines with enough ice to bring them down, resulting in widespread
damage and power outages.

If the cold air layer below the rain is cold enough and deep enough the
raindrops will partly or wholly re-freeze to ice before reaching the
ground. This is what our American cousins call "sleet".

--
- Yokel -

Yokel posts via a spam-trap account which is not read.